From cfed9374b7e162686857b071f2bb0362cd4447b5 Mon Sep 17 00:00:00 2001
From: Mihai Nita <nmihai_2000@yahoo.com>
Date: Mon, 24 Mar 2025 12:37:00 -0700
Subject: [PATCH] ICU-23040 Doclet migration: the real move from the JDK 8 APIs

---
 icu4j/pom.xml                                 |   16 +-
 icu4j/releases_tools/api_reports.sh           |    6 +-
 icu4j/releases_tools/github_release.sh        |    4 +-
 icu4j/releases_tools/shared.sh                |   11 +-
 icu4j/tools/build/pom.xml                     |   30 +-
 .../com/ibm/icu/dev/tool/docs/CheckAPI.java   | 1052 -----------------
 .../com/ibm/icu/dev/tool/docs/CheckTags.java  |  289 ++---
 .../ibm/icu/dev/tool/docs/GatherAPIData.java  |  706 ++++++-----
 .../icu/dev/tool/docs/GatherAPIDataOld.java   |  509 --------
 .../ibm/icu/dev/tool/docs/JavadocHelper.java  |  383 ++++++
 10 files changed, 953 insertions(+), 2053 deletions(-)
 delete mode 100644 icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/CheckAPI.java
 delete mode 100644 icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/GatherAPIDataOld.java
 create mode 100644 icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/JavadocHelper.java

diff --git a/icu4j/pom.xml b/icu4j/pom.xml
index 4eae13eb387..0174b78e676 100644
--- a/icu4j/pom.xml
+++ b/icu4j/pom.xml
@@ -688,21 +688,6 @@
       </build>
     </profile>
 
-    <!-- The tools/build module depends on the old tools.jar (jdk 1.8)
-      The com.sun.javadoc package was deprecated in Java 11, and has been removed for Java 17.
-      JDK 11 does not include tools.jar anymore. The code must be updated, see migration guide at
-        https://docs.oracle.com/en/java/javase/11/docs/api/jdk.javadoc/jdk/javadoc/doclet/package-summary.html#migration
-    -->
-    <profile>
-      <id>old_jdk_taglet</id>
-      <activation>
-        <jdk>[1.7,1.8]</jdk>
-      </activation>
-      <modules>
-         <module>tools/build</module>
-      </modules>
-    </profile>
-
     <!-- Starting with JDK 9, the Java compiler supports the −−release version.
       Unlike source (checking the language features) and target (the version of the classes generated),
       this option also checks that newer APIs are not used.
@@ -716,6 +701,7 @@
         <jdk>[9,)</jdk>
       </activation>
       <modules>
+         <module>tools/build</module>
          <module>tools/taglets</module>
       </modules>
       <build>
diff --git a/icu4j/releases_tools/api_reports.sh b/icu4j/releases_tools/api_reports.sh
index 1d9452aa75b..fcd08e32bbc 100755
--- a/icu4j/releases_tools/api_reports.sh
+++ b/icu4j/releases_tools/api_reports.sh
@@ -11,8 +11,8 @@ fi
 # ====================================================================================
 # The start of the script proper
 
-reportTitle "Checking the JDK version (must be 8)"
-checkThatJdk8IsDefault
+reportTitle "Checking the JDK version (must be newer than 8)"
+checkThatJdk8IsNotDefault
 
 # ====================================================================================
 
@@ -22,7 +22,7 @@ mvn clean -q --batch-mode
 # Build everything
 mvn install -q --batch-mode -DskipITs -DskipTests
 # Gather API info
-mvn site -q  --batch-mode -DskipITs -DskipTests -P gatherapi > /dev/null
+mvn site -q --batch-mode -DskipITs -DskipTests -P gatherapi > /dev/null
 
 checkFileCreated "${out_dir}/icu4j${api_report_version}.api3.gz"
 
diff --git a/icu4j/releases_tools/github_release.sh b/icu4j/releases_tools/github_release.sh
index c116f26096d..91f42b0ba20 100755
--- a/icu4j/releases_tools/github_release.sh
+++ b/icu4j/releases_tools/github_release.sh
@@ -24,8 +24,8 @@ function copyArtifactForGithubRelease() {
 # The start of the script proper
 
 release_folder=${out_dir}/github_release
-# We still need JDK 8 to generate the javadoc (because of the doclets)
-checkThatJdk8IsDefault
+# We can't use JDK 8 to generate the javadoc (because of the doclets)
+checkThatJdk8IsNotDefault
 
 # ====================================================================================
 # Build artifacts and copy them in the output folder
diff --git a/icu4j/releases_tools/shared.sh b/icu4j/releases_tools/shared.sh
index abb320ec49f..1b7f82c1855 100755
--- a/icu4j/releases_tools/shared.sh
+++ b/icu4j/releases_tools/shared.sh
@@ -11,16 +11,15 @@ export api_report_version='77'
 export api_report_prev_version='76'
 export out_dir=target
 
-function checkThatJdk8IsDefault() {
+function checkThatJdk8IsNotDefault() {
   javac -version appPath 2>&1 | grep -E 'javac 1\.8\.' > /dev/null
   if [ $? -eq 0 ]; then
-    echo "The default JDK is JDK 8, all good!"
-    javac -version
-  else
-    echo "This step can only be executed with JDK 8!"
-    echo "Make sure that you have the PATH pointing to a JDK 8!"
+    echo "This step can only be executed with a JDK newer than 8!"
     javac -version
     exit
+  else
+    echo "The default JDK is newer than JDK 8, all good!"
+    javac -version
   fi
 
 }
diff --git a/icu4j/tools/build/pom.xml b/icu4j/tools/build/pom.xml
index 57a078e61ff..98b0382c2f5 100644
--- a/icu4j/tools/build/pom.xml
+++ b/icu4j/tools/build/pom.xml
@@ -15,17 +15,27 @@
   <artifactId>tools_build</artifactId>
 
   <properties>
-    <icu4j.api.doc.root.dir>${project.basedir}/../..</icu4j.api.doc.root.dir>
+    <maven.compiler.source>11</maven.compiler.source>
+    <maven.compiler.target>11</maven.compiler.target>
   </properties>
 
-  <dependencies>
-    <dependency>
-      <groupId>jdk.tools</groupId>
-      <artifactId>jdk.tools</artifactId>
-      <version>1.8</version>
-      <scope>system</scope>
-      <systemPath>${JAVA_HOME}/lib/tools.jar</systemPath>
-    </dependency>
-  </dependencies>
+  <profiles>
+    <profile>
+      <id>newer_jdk</id>
+      <activation>
+        <jdk>[11,)</jdk>
+      </activation>
+      <build>
+        <plugins>
+          <plugin>
+            <artifactId>maven-compiler-plugin</artifactId>
+            <configuration>
+              <release>11</release>
+            </configuration>
+          </plugin>
+        </plugins>
+      </build>
+    </profile>
+  </profiles>
 
 </project>
diff --git a/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/CheckAPI.java b/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/CheckAPI.java
deleted file mode 100644
index 3718ec2376e..00000000000
--- a/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/CheckAPI.java
+++ /dev/null
@@ -1,1052 +0,0 @@
-// © 2016 and later: Unicode, Inc. and others.
-// License & terms of use: http://www.unicode.org/copyright.html
-/**
-*******************************************************************************
-* Copyright (C) 2004-2010, International Business Machines Corporation and         *
-* others. All Rights Reserved.                                                *
-*******************************************************************************
-*/
-
-/**
- * Generate a list of ICU's public APIs, sorted by qualified name and signature
- * public APIs are all non-internal, non-package apis in com.ibm.icu.[lang|math|text|util].
- * For each API, list
- * - public, package, protected, or private (PB PK PT PR)
- * - static or non-static (STK NST)
- * - final or non-final (FN NF)
- * - synchronized or non-synchronized (SYN NSY)
- * - stable, draft, deprecated, obsolete (ST DR DP OB)
- * - abstract or non-abstract (AB NA)
- * - constructor, member, field (C M F)
- *
- * Requires JDK 1.4.2 or later
- * 
- * Sample invocation:
- * c:/j2sdk1.4.2/bin/javadoc 
- *   -classpath c:/jd2sk1.4.2/lib/tools.jar 
- *   -doclet com.ibm.icu.dev.tool.docs.CheckAPI 
- *   -docletpath c:/doug/cvsproj/icu4j/src 
- *   -sourcepath c:/eclipse2.1/workspace2/icu4j/src 
- *   -compare c:/doug/cvsproj/icu4j/src/com/ibm/icu/dev/tool/docs/api2_6_1.txt 
- *   -output foo 
- *   com.ibm.icu.text
- *
- * todo: separate generation of data files (which requires taglet) from 
- * comparison and report generation (which does not require it)
- * todo: provide command-line control of filters of which subclasses/packages to process
- * todo: record full inheritance hierarchy, not just immediate inheritance 
- * todo: allow for aliasing comparisons (force (pkg.)*class to be treated as though it 
- * were in a different pkg/class hierarchy (facilitates comparison of icu4j and java)
- */
-
-package com.ibm.icu.dev.tool.docs;
-
-import java.io.BufferedReader;
-import java.io.BufferedWriter;
-import java.io.File;
-import java.io.FileInputStream;
-import java.io.FileNotFoundException;
-import java.io.FileOutputStream;
-import java.io.IOException;
-import java.io.InputStream;
-import java.io.InputStreamReader;
-import java.io.OutputStream;
-import java.io.OutputStreamWriter;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Comparator;
-import java.util.Iterator;
-import java.util.TreeSet;
-
-import com.sun.javadoc.ClassDoc;
-import com.sun.javadoc.ConstructorDoc;
-import com.sun.javadoc.Doc;
-import com.sun.javadoc.ExecutableMemberDoc;
-import com.sun.javadoc.FieldDoc;
-import com.sun.javadoc.MethodDoc;
-import com.sun.javadoc.ProgramElementDoc;
-import com.sun.javadoc.RootDoc;
-import com.sun.javadoc.Tag;
-
-public class CheckAPI {
-    RootDoc root;
-    String compare; // file
-    String compareName;
-    TreeSet compareSet;
-    TreeSet results;
-    boolean html;
-    String srcName = "Current"; // default source name
-    String output;
-    
-    private static final int DATA_FILE_VERSION = 1;
-    private static final char SEP = ';';
-
-    private static final int STA = 0, STA_DRAFT = 0, STA_STABLE = 1, STA_DEPRECATED = 2, STA_OBSOLETE = 3;
-    private static final int VIS = 1, VIS_PACKAGE = 0, VIS_PUBLIC= 1, VIS_PROTECTED = 2, VIS_PRIVATE = 3;
-    private static final int STK = 2, STK_STATIC = 1;
-    private static final int FIN = 3, FIN_FINAL = 1;
-    private static final int SYN = 4, SYN_SYNCHRONIZED = 1;
-    private static final int ABS = 5, ABS_ABSTRACT = 1;
-    private static final int CAT = 6, CAT_CLASS = 0, CAT_FIELD = 1, CAT_CONSTRUCTOR = 2, CAT_METHOD = 3;
-    private static final int PAK = 7;
-    private static final int CLS = 8;
-    private static final int NAM = 9;
-    private static final int SIG = 10;
-    private static final int EXC = 11;
-    private static final int NUM_TYPES = 11;
-
-    static abstract class APIInfo {
-        public abstract int getVal(int typ);
-        public abstract String get(int typ, boolean brief);
-        public abstract void write(BufferedWriter w, boolean brief, boolean html, boolean detail);
-    }
-        
-    final static class Info extends APIInfo {
-        private int    info;
-        private String pack; // package
-        private String cls; // enclosing class
-        private String name; // name
-        private String sig;  // signature, class: inheritance, method: signature, field: type, const: signature
-        private String exc;  // throws 
-        
-        public int getVal(int typ) {
-            validateType(typ);
-            return (info >> (typ*2)) & 0x3;
-        }
-
-        public String get(int typ, boolean brief) {
-            validateType(typ);
-            String[] vals = brief ? shortNames[typ] : names[typ];
-            if (vals == null) {
-                switch (typ) {
-                case PAK: return pack;
-                case CLS: return cls;
-                case NAM: return name;
-                case SIG: return sig;
-                case EXC: return exc;
-                }
-            }
-            int val = (info >> (typ*2)) & 0x3;
-            return vals[val];
-        }
-
-        private void setType(int typ, int val) {
-            validateType(typ);
-            info &= ~(0x3 << (typ*2));
-            info |= (val&0x3) << (typ * 2);
-        }
-
-        private void setType(int typ, String val) {
-            validateType(typ);
-            String[] vals = shortNames[typ];
-            if (vals == null) {
-                switch (typ) {
-                case PAK: pack = val; break;
-                case CLS: cls = val; break;
-                case NAM: name = val; break;
-                case SIG: sig = val; break;
-                case EXC: exc = val; break;
-                }
-                return;
-            }
-
-            for (int i = 0; i < vals.length; ++i) {
-                if (val.equalsIgnoreCase(vals[i])) {
-                    info &= ~(0x3 << (typ*2));
-                    info |= i << (typ*2);
-                    return;
-                }
-            }
-
-            throw new IllegalArgumentException("unrecognized value '" + val + "' for type '" + typeNames[typ] + "'");
-        }
-
-        public void write(BufferedWriter w, boolean brief, boolean html, boolean detail) {
-            try {
-                if (brief) {
-                    for (int i = 0; i < NUM_TYPES; ++i) {
-                        String s = get(i, true);
-                        if (s != null) {
-                            w.write(s);
-                        }
-                        w.write(SEP);
-                    }
-                } else {
-                    // remove all occurrences of icu packages from the param string
-                    // fortunately, all the packages have 4 chars (lang, math, text, util).
-                    String xsig = sig;
-                    if (!detail) {
-                        final String ICUPACK = "com.ibm.icu.";
-                        StringBuffer buf = new StringBuffer();
-                        for (int i = 0; i < sig.length();) {
-                            int n = sig.indexOf(ICUPACK, i);
-                            if (n == -1) {
-                                buf.append(sig.substring(i));
-                                break;
-                            }
-                            buf.append(sig.substring(i, n));
-                            i = n + ICUPACK.length() + 5; // trailing 'xxxx.'
-                        }
-                        xsig = buf.toString();
-                    }
-
-                    // construct signature
-                    for (int i = STA; i < CAT; ++i) { // include status
-                        String s = get(i, false);
-                        if (s != null && s.length() > 0) {
-                            if (i == STA) {
-                                w.write('(');
-                                w.write(s);
-                                w.write(')');
-                            } else {
-                                w.write(s);
-                            }
-                            w.write(' ');
-                        }
-                    }
-
-                    int val = getVal(CAT);
-                    switch (val) {
-                    case CAT_CLASS:
-                        if (sig.indexOf("extends") == -1) {
-                            w.write("interface ");
-                        } else {
-                            w.write("class ");
-                        }
-                        if (cls.length() > 0) {
-                            w.write(cls);
-                            w.write('.');
-                        }
-                        w.write(name);
-                        if (detail) {
-                            w.write(' ');
-                            w.write(sig);
-                        }
-                        break;
-
-                    case CAT_FIELD:
-                        w.write(xsig);
-                        w.write(' ');
-                        w.write(name);
-                        break;
-
-                    case CAT_METHOD:
-                    case CAT_CONSTRUCTOR:
-                        int n = xsig.indexOf('(');
-                        if (n > 0) {
-                            w.write(xsig.substring(0, n));
-                            w.write(' ');
-                        } else {
-                            n = 0;
-                        }
-                        w.write(name);
-                        w.write(xsig.substring(n));
-                        break;
-                    }
-                }
-                w.newLine();
-            }
-            catch (IOException e) {
-                RuntimeException re = new RuntimeException("IO Error");
-                re.initCause(e);
-                throw re;
-            }
-        }
-
-        public boolean read(BufferedReader r) {
-            int i = 0;
-            try {
-                for (; i < NUM_TYPES; ++i) {
-                    setType(i, readToken(r));
-                }
-                r.readLine(); // swallow line end sequence
-            }
-            catch (IOException e) {
-                if (i == 0) { // assume if first read returns error, we have reached end of input
-                    return false;
-                }
-                RuntimeException re = new RuntimeException("IO Error");
-                re.initCause(e);
-                throw re;
-            }
-
-            return true;
-        }
-
-        public boolean read(ProgramElementDoc doc) {
-
-            // Doc. name
-            // Doc. isField, isMethod, isConstructor, isClass, isInterface
-            // ProgramElementDoc. containingClass, containingPackage
-            // ProgramElementDoc. isPublic, isProtected, isPrivate, isPackagePrivate
-            // ProgramElementDoc. isStatic, isFinal
-            // MemberDoc.isSynthetic
-            // ExecutableMemberDoc isSynchronized, signature
-            // Type.toString() // e.g. "String[][]"
-            // ClassDoc.isAbstract, superClass, interfaces, fields, methods, constructors, innerClasses
-            // FieldDoc type
-            // ConstructorDoc qualifiedName
-            // MethodDoc isAbstract, returnType
-
-            
-            // status
-            setType(STA, tagStatus(doc));
-
-            // visibility
-            if (doc.isPublic()) {
-                setType(VIS, VIS_PUBLIC);
-            } else if (doc.isProtected()) {
-                setType(VIS, VIS_PROTECTED);
-            } else if (doc.isPrivate()) {
-                setType(VIS, VIS_PRIVATE);
-            } else {
-                // default is package
-            }
-
-            // static
-            if (doc.isStatic()) {
-                setType(STK, STK_STATIC);
-            } else {
-                // default is non-static
-            }
-
-            // final
-            if (doc.isFinal()) {
-                setType(FIN, FIN_FINAL);
-            } else {
-                // default is non-final
-            }
-
-            // type
-            if (doc.isField()) {
-                setType(CAT, CAT_FIELD);
-            } else if (doc.isMethod()) {
-                setType(CAT, CAT_METHOD);
-            } else if (doc.isConstructor()) {
-                setType(CAT, CAT_CONSTRUCTOR);
-            } else if (doc.isClass() || doc.isInterface()) {
-                setType(CAT, CAT_CLASS);
-            }
-
-            setType(PAK, doc.containingPackage().name());
-            setType(CLS, (doc.isClass() || doc.isInterface() || (doc.containingClass() == null)) ? "" : doc.containingClass().name());
-            setType(NAM, doc.name());
-
-            if (doc instanceof FieldDoc) {
-                FieldDoc fdoc = (FieldDoc)doc;
-                setType(SIG, fdoc.type().toString());
-            } else if (doc instanceof ClassDoc) {
-                ClassDoc cdoc = (ClassDoc)doc;
-
-                if (cdoc.isClass() && cdoc.isAbstract()) { // interfaces are abstract by default, don't mark them as abstract
-                    setType(ABS, ABS_ABSTRACT);
-                }
-
-                StringBuffer buf = new StringBuffer();
-                if (cdoc.isClass()) {
-                    buf.append("extends ");
-                    buf.append(cdoc.superclass().qualifiedName());
-                }
-                ClassDoc[] imp = cdoc.interfaces();
-                if (imp != null && imp.length > 0) {
-                    if (buf.length() > 0) {
-                        buf.append(" ");
-                    }
-                    buf.append("implements");
-                    for (int i = 0; i < imp.length; ++i) {
-                        if (i != 0) {
-                            buf.append(",");
-                        }
-                        buf.append(" ");
-                        buf.append(imp[i].qualifiedName());
-                    }
-                }
-                setType(SIG, buf.toString());
-            } else {
-                ExecutableMemberDoc emdoc = (ExecutableMemberDoc)doc;
-                if (emdoc.isSynchronized()) {
-                    setType(SYN, SYN_SYNCHRONIZED);
-                }
-
-                if (doc instanceof MethodDoc) {
-                    MethodDoc mdoc = (MethodDoc)doc;
-                    if (mdoc.isAbstract()) {
-                        setType(ABS, ABS_ABSTRACT);
-                    }
-                    setType(SIG, mdoc.returnType().toString() + emdoc.signature());
-                } else {
-                    // constructor
-                    setType(SIG, emdoc.signature());
-                }
-            }
-
-            return true;
-        }
-
-        public static Comparator defaultComparator() {
-            final Comparator c = new Comparator() {
-                    public int compare(Object lhs, Object rhs) {
-                        Info lhi = (Info)lhs;
-                        Info rhi = (Info)rhs;
-                        int result = lhi.pack.compareTo(rhi.pack);
-                        if (result == 0) {
-                            result = (lhi.getVal(CAT) == CAT_CLASS ? lhi.name : lhi.cls)
-                                .compareTo(rhi.getVal(CAT) == CAT_CLASS ? rhi.name : rhi.cls);
-                            if (result == 0) {
-                                result = lhi.getVal(CAT)- rhi.getVal(CAT);
-                                if (result == 0) {
-                                    result = lhi.name.compareTo(rhi.name);
-                                    if (result == 0) {
-                                        result = lhi.sig.compareTo(rhi.sig);
-                                    }
-                                }
-                            }
-                        }
-                        return result;
-                    }
-                };
-            return c;
-        }
-
-        public static Comparator changedComparator() {
-            final Comparator c = new Comparator() {
-                    public int compare(Object lhs, Object rhs) {
-                        Info lhi = (Info)lhs;
-                        Info rhi = (Info)rhs;
-                        int result = lhi.pack.compareTo(rhi.pack);
-                        if (result == 0) {
-                            result = (lhi.getVal(CAT) == CAT_CLASS ? lhi.name : lhi.cls)
-                                .compareTo(rhi.getVal(CAT) == CAT_CLASS ? rhi.name : rhi.cls);
-                            if (result == 0) {
-                                result = lhi.getVal(CAT)- rhi.getVal(CAT);
-                                if (result == 0) {
-                                    result = lhi.name.compareTo(rhi.name);
-                                    if (result == 0 && lhi.getVal(CAT) != CAT_CLASS) {
-                                        result = lhi.sig.compareTo(rhi.sig);
-                                    }
-                                }
-                            }
-                        }
-                        return result;
-                    }
-                };
-            return c;
-        }
-
-        public static Comparator classFirstComparator() {
-            final Comparator c = new Comparator() {
-                    public int compare(Object lhs, Object rhs) {
-                        Info lhi = (Info)lhs;
-                        Info rhi = (Info)rhs;
-                        int result = lhi.pack.compareTo(rhi.pack);
-                        if (result == 0) {
-                            boolean lcls = lhi.getVal(CAT) == CAT_CLASS;
-                            boolean rcls = rhi.getVal(CAT) == CAT_CLASS;
-                            result = lcls == rcls ? 0 : (lcls ? -1 : 1);
-                            if (result == 0) {
-                                result = (lcls ? lhi.name : lhi.cls).compareTo(rcls ? rhi.name : rhi.cls);
-                                if (result == 0) {
-                                    result = lhi.getVal(CAT)- rhi.getVal(CAT);
-                                    if (result == 0) {
-                                        result = lhi.name.compareTo(rhi.name);
-                                        if (result == 0 && !lcls) {
-                                            result = lhi.sig.compareTo(rhi.sig);
-                                        }
-                                    }
-                                }
-                            }
-                        }
-                        return result;
-                    }
-                };
-            return c;
-        }
-
-        private static final String[] typeNames = {
-            "status", "visibility", "static", "final", "synchronized", 
-            "abstract", "category", "package", "class", "name", "signature"
-        };
-
-        private static final String[][] names = {
-            { "draft     ", "stable    ", "deprecated", "obsolete  " },
-            { "package", "public", "protected", "private" },
-            { "", "static" },
-            { "", "final" },
-            { "", "synchronized" },
-            { "", "abstract" },
-            { "class", "field", "constructor", "method"  },
-            null,
-            null,
-            null,
-            null,
-            null
-        };
-
-        private static final String[][] shortNames = {
-            { "DR", "ST", "DP", "OB" },
-            { "PK", "PB", "PT", "PR" },
-            { "NS", "ST" },
-            { "NF", "FN" },
-            { "NS", "SY" },
-            { "NA", "AB" },
-            { "L", "F", "C", "M" },
-            null,
-            null,
-            null,
-            null,
-            null
-        };
-
-        private static void validateType(int typ) {
-            if (typ < 0 || typ > NUM_TYPES) {
-                throw new IllegalArgumentException("bad type index: " + typ);
-            }
-        }
-
-        public String toString() {
-            return get(NAM, true);
-        }
-    }
-
-    static final class DeltaInfo extends APIInfo {
-        private Info a;
-        private Info b;
-
-        DeltaInfo(Info a, Info b) {
-            this.a = a;
-            this.b = b;
-        }
-
-        public int getVal(int typ) {
-            return a.getVal(typ);
-        }
-
-        public String get(int typ, boolean brief) {
-            return a.get(typ, brief);
-        }
-
-        public void write(BufferedWriter w, boolean brief, boolean html, boolean detail) {
-            a.write(w, brief, html, detail);
-            try {
-                if (html) {
-                    w.write("<br>");
-                }
-                w.newLine();
-            } 
-            catch (Exception e) {
-            }
-            b.write(w, brief, html, detail);
-        }
-
-        public String toString() {
-            return a.get(NAM, true);
-        }
-    }
-
-    public static int optionLength(String option) {
-        if (option.equals("-html")) {
-            return 1;
-        } else if (option.equals("-name")) {
-            return 2;
-        } else if (option.equals("-output")) {
-            return 2;
-        } else if (option.equals("-compare")) {
-            return 2;
-        }
-        return 0;
-    }
-
-    public static boolean start(RootDoc root) {
-        return new CheckAPI(root).run();
-    }
-
-    CheckAPI(RootDoc root) {
-        this.root = root;
-
-        //      this.compare = "c:/doug/cvsproj/icu4j/src/com/ibm/icu/dev/tool/docs/api2_8.txt";
-
-        String[][] options = root.options();
-        for (int i = 0; i < options.length; ++i) {
-            String opt = options[i][0];
-            if (opt.equals("-html")) {
-                this.html = true;
-            } else if (opt.equals("-name")) {
-                this.srcName = options[i][1];
-            } else if (opt.equals("-output")) {
-                this.output = options[i][1];
-            } else if (opt.equals("-compare")) {
-                this.compare = options[i][1];
-            }
-        }
-
-        if (compare != null) {
-            try {
-                // URL url = new URL(compare);
-                File f = new File(compare);
-                InputStream is = new FileInputStream(f);
-                InputStreamReader isr = new InputStreamReader(is);
-                BufferedReader br = new BufferedReader(isr);
-
-                // read header line
-                /*int version = */Integer.parseInt(readToken(br));
-                // check version if we change it later, probably can just rebuild though
-                this.compareName = readToken(br);
-                br.readLine();
-
-                // read data
-                this.compareSet = new TreeSet(Info.defaultComparator());
-                for (Info info = new Info(); info.read(br); info = new Info()) {
-                    compareSet.add(info);
-                }
-            }
-            catch (Exception e) {
-                RuntimeException re = new RuntimeException("error reading " + compare);
-                re.initCause(e);
-                throw re;
-            }
-        }
-            
-        results = new TreeSet(Info.defaultComparator());
-    }
-
-    private boolean run() {
-        doDocs(root.classes());
-
-        OutputStream os = System.out;
-        if (output != null) {
-            try {
-                os = new FileOutputStream(output);
-            }
-            catch (FileNotFoundException e) {
-                RuntimeException re = new RuntimeException(e.getMessage());
-                re.initCause(e);
-                throw re;
-            }
-        }
-
-        BufferedWriter bw = null;
-        try {
-            OutputStreamWriter osw = new OutputStreamWriter(os, "UTF-8");
-            bw = new BufferedWriter(osw);
-
-            if (compareSet == null) {
-                // writing data file
-                bw.write(String.valueOf(DATA_FILE_VERSION) + SEP); // header version
-                bw.write(srcName + SEP); // source name
-                bw.newLine();
-                writeResults(results, bw, true, false, false);
-            } else {
-                // writing comparison info
-                TreeSet removed = (TreeSet)compareSet.clone();
-                removed.removeAll(results);
-
-                TreeSet added = (TreeSet)results.clone();
-                added.removeAll(compareSet);
-
-                Iterator ai = added.iterator();
-                Iterator ri = removed.iterator();
-                ArrayList changed = new ArrayList();
-                Comparator c = Info.changedComparator();
-                Info a = null, r = null;
-                while (ai.hasNext() && ri.hasNext()) {
-                    if (a == null) a = (Info)ai.next();
-                    if (r == null) r = (Info)ri.next();
-                    int result = c.compare(a, r);
-                    if (result < 0) {
-                        a = null;
-                    } else if (result > 0) {
-                        r = null;
-                    } else {
-                        changed.add(new DeltaInfo(a, r));
-                        a = null; ai.remove();
-                        r = null; ri.remove();
-                    }
-                }
-
-                added = stripAndResort(added);
-                removed = stripAndResort(removed);
-
-                if (html) {
-                    String title = "ICU4J API Comparison: " + srcName + " with " + compareName;
-
-                    bw.write("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
-                    bw.newLine();
-                    bw.write("<html>");
-                    bw.newLine();
-                    bw.write("<head>");
-                    bw.newLine();
-                    bw.write("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\">");
-                    bw.newLine();
-                    bw.write("<title>");
-                    bw.write(title);
-                    bw.write("</title>");
-                    bw.newLine();
-                    bw.write("<body>");
-                    bw.newLine();
-
-                    bw.write("<h1>");
-                    bw.write(title);
-                    bw.write("</h1>");
-                    bw.newLine();
-
-                    bw.write("<hr/>");
-                    bw.newLine();
-                    bw.write("<h2>");
-                    bw.write("Removed from " + compareName);
-                    bw.write("</h2>");
-                    bw.newLine();
-
-                    if (removed.size() > 0) {
-                        writeResults(removed, bw, false, true, false);
-                    } else {
-                        bw.write("<p>(no API removed)</p>");
-                    }
-                    bw.newLine();
-
-                    bw.write("<hr/>");
-                    bw.newLine();
-                    bw.write("<h2>");
-                    bw.write("Changed in " + srcName);
-                    bw.write("</h2>");
-                    bw.newLine();
-
-                    if (changed.size() > 0) {
-                        writeResults(changed, bw, false, true, true);
-                    } else {
-                        bw.write("<p>(no API changed)</p>");
-                    }
-                    bw.newLine();
-
-                    bw.write("<hr/>");
-                    bw.newLine();
-                    bw.write("<h2>");
-                    bw.write("Added in " + srcName);
-                    bw.write("</h2>");
-                    bw.newLine();
-
-                    if (added.size() > 0) {
-                        writeResults(added, bw, false, true, false);
-                    } else {
-                        bw.write("<p>(no API added)</p>");
-                    }
-                    bw.write("<hr/>");
-                    bw.newLine();
-                    bw.write("<p><i>Contents generated by CheckAPI tool.<br/>Copyright (C) 2004, International Business Machines Corporation, All Rights Reserved.</i></p>");
-                    bw.newLine();
-                    bw.write("</body>");
-                    bw.newLine();
-                    bw.write("</html>");
-                    bw.newLine();
-                } else {
-                    bw.write("Comparing " + srcName + " with " + compareName);
-                    bw.newLine();
-                    bw.newLine();
-
-                    bw.newLine();
-                    bw.write("=== Removed from " + compareName + " ===");
-                    bw.newLine();
-                    if (removed.size() > 0) {
-                        writeResults(removed, bw, false, false, false);
-                    } else {
-                        bw.write("(no API removed)");
-                    }
-                    bw.newLine();
-
-                    bw.newLine();
-                    bw.write("=== Changed in " + srcName + " ===");
-                    bw.newLine();
-                    if (changed.size() > 0) {
-                        writeResults(changed, bw, false, false, true);
-                    } else {
-                        bw.write("(no API changed)");
-                    }
-                    bw.newLine();
-
-                    bw.newLine();
-                    bw.write("=== Added in " + srcName + " ===");
-                    bw.newLine();
-                    if (added.size() > 0) {
-                        writeResults(added, bw, false, false, false);
-                    } else {
-                        bw.write("(no API added)");
-                    }
-                    bw.newLine();
-                }
-            }
-
-            bw.close();
-        } catch (IOException e) {
-            try { bw.close(); } catch (IOException e2) {}
-            RuntimeException re = new RuntimeException("write error: " + e.getMessage());
-            re.initCause(e);
-            throw re;
-        }
-
-        return false;
-    }
-
-    private void doDocs(ProgramElementDoc[] docs) {
-        if (docs != null && docs.length > 0) {
-            for (int i = 0; i < docs.length; ++i) {
-                doDoc(docs[i]);
-            }
-        }
-    }
-
-    private void doDoc(ProgramElementDoc doc) {
-        if (ignore(doc)) return;
-
-        if (doc.isClass() || doc.isInterface()) {
-            ClassDoc cdoc = (ClassDoc)doc;
-            doDocs(cdoc.fields());
-            doDocs(cdoc.constructors());
-            doDocs(cdoc.methods());
-            doDocs(cdoc.innerClasses());
-        }
-
-        Info info = new Info();
-        if (info.read(doc)) {
-            results.add(info);
-        }
-    }
-
-    private boolean ignore(ProgramElementDoc doc) {
-        if (doc == null) return true;
-        if (doc.isPrivate() || doc.isPackagePrivate()) return true;
-        if (doc instanceof ConstructorDoc && ((ConstructorDoc)doc).isSynthetic()) return true;
-        if (doc.qualifiedName().indexOf(".misc") != -1) return true;
-        Tag[] tags = doc.tags();
-        for (int i = 0; i < tags.length; ++i) {
-            if (tagKindIndex(tags[i].kind()) == INTERNAL) return true;
-        }
-
-        return false;
-    }
-
-    private static void writeResults(Collection c, BufferedWriter w, boolean brief, boolean html, boolean detail) {
-        Iterator iter = c.iterator();
-        String pack = null;
-        String clas = null;
-        while (iter.hasNext()) {
-            APIInfo info = (APIInfo)iter.next();
-            if (brief) {
-                info.write(w, brief, false, detail);
-            } else {
-                try {
-                    String p = info.get(PAK, true);
-                    if (!p.equals(pack)) {
-                        w.newLine();
-                        if (html) {
-                            if (clas != null) {
-                                w.write("</ul>");
-                                w.newLine();
-                            }
-                            if (pack != null) {
-                                w.write("</ul>");
-                                w.newLine();
-                            }
-                            
-                            w.write("<h3>Package ");
-                            w.write(p);
-                            w.write("</h3>");
-                            w.newLine();
-                            w.write("<ul>");
-                            w.newLine();
-                        } else {
-                            w.write("Package ");
-                            w.write(p);
-                            w.write(':');
-                        }
-                        w.newLine();
-                        w.newLine();
-                        
-                        pack = p;
-                        clas = null;
-                    }
-
-                    if (info.getVal(CAT) != CAT_CLASS) {
-                        String name = info.get(CLS, true);
-                        if (!name.equals(clas)) {
-                            if (html) {
-                                if (clas != null) {
-                                    w.write("</ul>");
-                                }
-                                w.write("<li>");
-                                w.write(name);
-                                w.newLine();
-                                w.write("<ul>");
-                            } else {
-                                w.write(name);
-                                w.newLine();
-                            }
-                            clas = name;
-                        }
-                        w.write("    ");
-                    }
-                    if (html) {
-                        w.write("<li>");
-                        info.write(w, brief, html, detail);
-                        w.write("</li>");
-                    } else {
-                        info.write(w, brief, html, detail);
-                    }
-                }
-                catch (IOException e) {
-                    System.err.println("IOException " + e.getMessage() + " writing " + info);
-                }
-            }
-        }
-        if (html) {
-            try {
-                if (clas != null) {
-                    w.write("</ul>");
-                    w.newLine();
-                }
-                if (pack != null) {
-                    w.write("</ul>");
-                    w.newLine();
-                }
-            } 
-            catch (IOException e) {
-            }
-        }
-    }
-
-    private static String readToken(BufferedReader r) throws IOException {
-        char[] buf = new char[256];
-        int i = 0;
-        for (; i < buf.length; ++i) {
-            int c = r.read();
-            if (c == -1) {
-                throw new IOException("unexpected EOF");
-            } else if (c == SEP) {
-                break;
-            }
-            buf[i] = (char)c;
-        }
-        if (i == buf.length) {
-            throw new IOException("unterminated token" + new String(buf));
-        }
-            
-        return new String(buf, 0, i);
-    }
-
-    private static TreeSet stripAndResort(TreeSet t) {
-        stripClassInfo(t);
-        TreeSet r = new TreeSet(Info.classFirstComparator());
-        r.addAll(t);
-        return r;
-    }
-
-    private static void stripClassInfo(Collection c) {
-        // c is sorted with class info first
-        Iterator iter = c.iterator();
-        String cname = null;
-        while (iter.hasNext()) {
-            Info info = (Info)iter.next();
-            String cls = info.get(CLS, true);
-            if (cname != null) {
-                if (cname.equals(cls)) {
-                    iter.remove();
-                    continue;
-                }
-                cname = null;
-            } 
-            if (info.getVal(CAT) == CAT_CLASS) {
-                cname = info.get(NAM, true);
-            }
-        }
-    }
-
-    private static int tagStatus(final Doc doc) {
-        class Result {
-            int res = -1;
-            void set(int val) { if (res != -1) throw new RuntimeException("bad doc: " + doc); res = val; }
-            int get() {
-                if (res == -1) {
-                    System.err.println("warning: no tag for " + doc);
-                    return 0;
-                }
-                return res;
-            }
-        }
-
-        Tag[] tags = doc.tags();
-        Result result = new Result();
-        for (int i = 0; i < tags.length; ++i) {
-            Tag tag = tags[i];
-
-            String kind = tag.kind();
-            int ix = tagKindIndex(kind);
-
-            switch (ix) {
-            case INTERNAL:
-                result.set(-2);
-                break;
-
-            case DRAFT:
-                result.set(STA_DRAFT);
-                break;
-
-            case STABLE:
-                result.set(STA_STABLE);
-                break;
-
-            case DEPRECATED:
-                result.set(STA_DEPRECATED);
-                break;
-
-            case OBSOLETE:
-                result.set(STA_OBSOLETE);
-                break;
-
-            case SINCE:
-            case EXCEPTION:
-            case VERSION:
-            case UNKNOWN:
-            case AUTHOR:
-            case SEE:
-            case PARAM:
-            case RETURN:
-            case THROWS:
-            case SERIAL:
-                break;
-
-            default:
-                throw new RuntimeException("unknown index " + ix + " for tag: " + kind);
-            }
-        }
-
-        return result.get();
-    }
-
-    private static final int UNKNOWN = -1;
-    private static final int INTERNAL = 0;
-    private static final int DRAFT = 1;
-    private static final int STABLE = 2;
-    private static final int SINCE = 3;
-    private static final int DEPRECATED = 4;
-    private static final int AUTHOR = 5;
-    private static final int SEE = 6;
-    private static final int VERSION = 7;
-    private static final int PARAM = 8;
-    private static final int RETURN = 9;
-    private static final int THROWS = 10;
-    private static final int OBSOLETE = 11;
-    private static final int EXCEPTION = 12;
-    private static final int SERIAL = 13;
-
-    private static int tagKindIndex(String kind) {
-        final String[] tagKinds = {
-            "@internal", "@draft", "@stable", "@since", "@deprecated", "@author", "@see", "@version",
-            "@param", "@return", "@throws", "@obsolete", "@exception", "@serial"
-        };
-
-        for (int i = 0; i < tagKinds.length; ++i) {
-            if (kind.equals(tagKinds[i])) {
-                return i;
-            }
-        }
-        return UNKNOWN;
-    }
-}
diff --git a/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/CheckTags.java b/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/CheckTags.java
index 3e2121c24c5..a1fed3ecb9c 100644
--- a/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/CheckTags.java
+++ b/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/CheckTags.java
@@ -32,15 +32,32 @@
 
 package com.ibm.icu.dev.tool.docs;
 
-import com.sun.javadoc.ClassDoc;
-import com.sun.javadoc.ConstructorDoc;
-import com.sun.javadoc.ExecutableMemberDoc;
-import com.sun.javadoc.ProgramElementDoc;
-import com.sun.javadoc.RootDoc;
-import com.sun.javadoc.Tag;
+import java.util.Collection;
+import java.util.List;
+import java.util.Locale;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import javax.lang.model.SourceVersion;
+import javax.lang.model.element.Element;
+import javax.lang.model.element.ExecutableElement;
+import javax.lang.model.element.QualifiedNameable;
+import javax.lang.model.element.TypeElement;
+import javax.lang.model.util.Elements;
+
+import com.sun.source.doctree.BlockTagTree;
+import com.sun.source.doctree.DocTree;
+import com.sun.source.doctree.InlineTagTree;
+import com.sun.source.util.DocTrees;
+
+import jdk.javadoc.doclet.Doclet;
+import jdk.javadoc.doclet.DocletEnvironment;
+import jdk.javadoc.doclet.Reporter;
+
+public class CheckTags implements Doclet {
+    private DocTrees docTrees;
+    private Elements elements;
 
-public class CheckTags {
-    RootDoc root;
     boolean log;
     boolean brief;
     boolean isShort;
@@ -118,7 +135,7 @@ public class CheckTags {
             DocNode last = stack[ix];
             if (error) {
                 last.errorCount += 1;
-        }
+            }
 
             boolean show = !brief || last.reportError;
             // boolean nomsg = show && brief && error;
@@ -162,86 +179,61 @@ public class CheckTags {
         }
     }
 
-    public static boolean start(RootDoc root) {
-        return new CheckTags(root).run();
+    @Override
+    public SourceVersion getSupportedSourceVersion() {
+        // The documentation says "usually the latest version"
+        // But even if at this time JDK 23 is already released, we
+        // want to be able to compile / use this doclet with at least JDK 11.
+        // So anything above RELEASE_11 is undefined
+        return SourceVersion.RELEASE_11;
     }
 
-    public static int optionLength(String option) {
-        if (option.equals("-log")) {
-            return 1;
-        } else if (option.equals("-brief")) {
-            return 1;
-        } else if (option.equals("-short")) {
-            return 1;
-        }
-        return 0;
+    @Override
+    public void init(Locale locale, Reporter reporter) {
     }
 
-    CheckTags(RootDoc root) {
-        this.root = root;
+    @Override
+    public String getName() {
+        return this.getClass().getSimpleName();
+    }
 
-        String[][] options = root.options();
-        for (int i = 0; i < options.length; ++i) {
-            String opt = options[i][0];
-            if (opt.equals("-log")) {
-                this.log = true;
-            } else if (opt.equals("-brief")) {
-                this.brief = true;
-            } else if (opt.equals("-short")) {
-                this.isShort = true;
+    @Override
+    public Set<Option> getSupportedOptions() {
+        return SUPPORTED_OPTIONS;
+    }
+
+    private final static Set<Option> SUPPORTED_OPTIONS = Set.of(
+            new JavadocHelper.GatherApiDataOption(0, "-log", "log", "the description of name"),
+            new JavadocHelper.GatherApiDataOption(0, "-brief", "brief", "the description of output"),
+            new JavadocHelper.GatherApiDataOption(0, "-short", "short", "the description of base"));
+
+    private void initFromOptions() {
+        for (Option opt : SUPPORTED_OPTIONS) {
+            JavadocHelper.GatherApiDataOption option = (JavadocHelper.GatherApiDataOption) opt;
+            switch (option.getName()) {
+                case "-log":
+                    this.log = option.getBooleanValue(false);
+                    break;
+                case "-brief":
+                    this.brief = option.getBooleanValue(false);
+                    break;
+                case "-isShort":
+                    this.isShort = option.getBooleanValue(false);
+                    break;
             }
         }
     }
 
-    boolean run() {
-        doDocs(root.classes(), "Package", true);
-        return false;
-    }
-
-    static final String[] tagKinds = {
-        "@internal", "@draft", "@stable", "@since", "@deprecated", "@author", "@see", "@version",
-        "@param", "@return", "@throws", "@obsolete", "@exception", "@serial", "@provisional"
-    };
-
-    static final int UNKNOWN = -1;
-    static final int INTERNAL = 0;
-    static final int DRAFT = 1;
-    static final int STABLE = 2;
-    static final int SINCE = 3;
-    static final int DEPRECATED = 4;
-    static final int AUTHOR = 5;
-    static final int SEE = 6;
-    static final int VERSION = 7;
-    static final int PARAM = 8;
-    static final int RETURN = 9;
-    static final int THROWS = 10;
-    static final int OBSOLETE = 11;
-    static final int EXCEPTION = 12;
-    static final int SERIAL = 13;
-    static final int PROVISIONAL = 14;
-
-    static int tagKindIndex(String kind) {
-        for (int i = 0; i < tagKinds.length; ++i) {
-            if (kind.equals(tagKinds[i])) {
-                return i;
-            }
-        }
-        return UNKNOWN;
-    }
-
-    static final String[] icuTagNames = {
-        "@icu", "@icunote", "@icuenhanced"
-    };
-    static final int ICU = 0;
-    static final int ICUNOTE = 1;
-    static final int ICUENHANCED = 2;
-    static int icuTagIndex(String name) {
-        for (int i = 0; i < icuTagNames.length; ++i) {
-            if (icuTagNames[i].equals(name)) {
-                return i;
-            }
-        }
-        return UNKNOWN;
+    @Override
+    public boolean run(DocletEnvironment environment) {
+        docTrees = environment.getDocTrees();
+        elements = environment.getElementUtils();
+        initFromOptions();
+        List<? extends Element> allClasses = environment.getIncludedElements().stream()
+                .filter(e-> e.getKind().isClass())
+                .collect(Collectors.toList());
+        doDocs(allClasses, "Package", true);
+        return true;
     }
 
     boolean newline = false;
@@ -274,46 +266,45 @@ public class CheckTags {
         output(msg, true, true);
     }
 
-    void tagErr(String msg, Tag tag) {
-        // Tag.position() requires JDK 1.4, build.xml tests for this
+    void tagErr(String msg, Element element, DocTree tag) {
         if (msg.length() > 0) {
             msg += ": ";
         }
-        errln(msg + tag.toString() + " [" + tag.position() + "]");
+        errln(msg + tag.toString() + " [" + JavadocHelper.position(elements, docTrees, element, tag) + "]");
     };
 
-    void tagErr(Tag tag) {
-        tagErr("", tag);
+    void tagErr(Element element, BlockTagTree tag) {
+        tagErr("", element, tag);
     }
 
-    void doDocs(ProgramElementDoc[] docs, String header, boolean reportError) {
-        if (docs != null && docs.length > 0) {
+    void doDocs(Collection<? extends Element> elements, String header, boolean reportError) {
+        if (elements != null && !elements.isEmpty()) {
             stack.push(header, reportError);
-            for (int i = 0; i < docs.length; ++i) {
-                doDoc(docs[i]);
+            for (Element element : elements) {
+                doDoc(element);
             }
             stack.pop();
         }
     }
 
-    void doDoc(ProgramElementDoc doc) {
-        if (doc != null && (doc.isPublic() || doc.isProtected())
-            && !(doc instanceof ConstructorDoc && ((ConstructorDoc)doc).isSynthetic())) {
-
+    void doDoc(Element doc) {
+        if (doc != null && (JavadocHelper.isPublic(doc) || JavadocHelper.isProtected(doc))
+            && !(JavadocHelper.isKindConstructor(doc) && JavadocHelper.isSynthetic(elements, doc))) {
             // unfortunately, in JDK 1.4.1 MemberDoc.isSynthetic is not properly implemented for
             // synthetic constructors.  So you'll have to live with spurious errors or 'implement'
             // the synthetic constructors...
 
-            boolean isClass = doc.isClass() || doc.isInterface();
+            boolean isClass = JavadocHelper.isKindClassOrInterface(doc);
             String header;
             if (!isShort || isClass) {
                 header = "--- ";
             } else {
                 header = "";
             }
-            header += (isClass ? doc.qualifiedName() : doc.name());
-            if (doc instanceof ExecutableMemberDoc) {
-                header += ((ExecutableMemberDoc)doc).flatSignature();
+            if (doc instanceof ExecutableElement) {
+                header += JavadocHelper.flatSignature(doc);
+            } else {
+                header += (isClass ? ((QualifiedNameable) doc).getQualifiedName() : doc.getSimpleName());
             }
             if (!isShort || isClass) {
                 header += " ---";
@@ -324,17 +315,23 @@ public class CheckTags {
             }
             boolean recurse = doTags(doc);
             if (recurse && isClass) {
-                ClassDoc cdoc = (ClassDoc)doc;
-                doDocs(cdoc.fields(), "Fields", !brief);
-                doDocs(cdoc.constructors(), "Constructors", !brief);
-                doDocs(cdoc.methods(), "Methods", !brief);
+                TypeElement cdoc = (TypeElement)doc;
+                List<? extends Element> fields = cdoc.getEnclosedElements().stream()
+                        .filter(JavadocHelper::isKindField).collect(Collectors.toList());
+                doDocs(fields, "Fields", !brief);
+                List<? extends Element> constructors = cdoc.getEnclosedElements().stream()
+                        .filter(JavadocHelper::isKindConstructor).collect(Collectors.toList());
+                doDocs(constructors, "Constructors", !brief);
+                List<? extends Element> methods = cdoc.getEnclosedElements().stream()
+                        .filter(JavadocHelper::isKindMethod).collect(Collectors.toList());
+                doDocs(methods, "Methods", !brief);
             }
             stack.pop();
         }
     }
 
     /** Return true if subelements of this doc should be checked */
-    boolean doTags(ProgramElementDoc doc) {
+    boolean doTags(Element doc) {
         boolean foundRequiredTag = false;
         boolean foundDraftTag = false;
         boolean foundProvisionalTag = false;
@@ -344,45 +341,52 @@ public class CheckTags {
         boolean foundStableTag = false;
         boolean retainAll = false;
 
+        if (JavadocHelper.isIgnoredEnumMethod(doc)) {
+            return false;
+        }
+
         // first check inline tags
-        for (Tag tag : doc.inlineTags()) {
-            int index = icuTagIndex(tag.name());
-            if (index >= 0) {
-                String text = tag.text().trim();
-                switch (index) {
+        for (InlineTagTree tag : JavadocHelper.getInnerTags(docTrees, doc)) {
+            JavadocHelper.IcuTagKind index = JavadocHelper.IcuTagKind.ofTag(tag);
+            String text = JavadocHelper.toText(tag).trim();
+            // System.out.println("SPY    ==== " + tag + " === " + index + " == '" + text + "'");
+            switch (index) {
                 case ICU: {
-                    if (doc.isClass() || doc.isInterface()) {
-                        tagErr("tag should appear only in member docs", tag);
+                    if (JavadocHelper.isKindClassOrInterface(doc)) {
+                        tagErr("tag should appear only in member docs", doc, tag);
                     }
                 } break;
                 case ICUNOTE: {
-                    if (text.length() > 0) {
-                        tagErr("tag should not contain text", tag);
+                    if (!text.isEmpty()) {
+                        tagErr("tag should not contain text", doc, tag);
                     }
                 } break;
                 case ICUENHANCED: {
-                    if (text.length() == 0) {
-                        tagErr("text should name related jdk class", tag);
+                    if (text.isEmpty()) {
+                        tagErr("text should name related jdk class", doc, tag);
                     }
-                    if (!(doc.isClass() || doc.isInterface())) {
-                        tagErr("tag should appear only in class/interface docs", tag);
+                    if (!(JavadocHelper.isKindClassOrInterface(doc))) {
+                        tagErr("tag should appear only in class/interface docs", doc, tag);
                     }
                 } break;
-                default:
-                    tagErr("unrecognized tag index for tag", tag);
+                case UNKNOWN:
+                    // It might be a standard tag, so we don't complain about this
+                    break;
+                default:
+                    tagErr("unrecognized tag index for tag", doc, tag);
                     break;
-                }
             }
         }
 
+        // System.out.println("SPY====== " + doc);
         // next check regular tags
-        for (Tag tag : doc.tags()) {
-            String kind = tag.kind();
-            int ix = tagKindIndex(kind);
-
+        for (BlockTagTree tag : JavadocHelper.getBlockTags(docTrees, doc)) {
+            JavadocHelper.TagKind ix = JavadocHelper.TagKind.ofTag(tag);
+            String tagText = JavadocHelper.toText(tag);
+            // System.out.println("SPY    ==== " + tag + " === " + ix + " == '" + tagText + "'");
             switch (ix) {
             case UNKNOWN:
-                errln("unknown kind: " + kind);
+                errln("unknown kind: " + tag.getTagName());
                 break;
 
             case INTERNAL:
@@ -393,16 +397,16 @@ public class CheckTags {
             case DRAFT:
                 foundRequiredTag = true;
                 foundDraftTag = true;
-                if (tag.text().indexOf("ICU 2.8") != -1 &&
-                    tag.text().indexOf("(retain") == -1) { // catch both retain and retainAll
-                    tagErr(tag);
+                if (tagText.indexOf("ICU 2.8") != -1 &&
+                        tagText.indexOf("(retain") == -1) { // catch both retain and retainAll
+                    tagErr(doc, tag);
                     break;
                 }
-                if (tag.text().indexOf("ICU") != 0) {
-                    tagErr(tag);
+                if (tagText.indexOf("ICU") != 0) {
+                    tagErr(doc, tag);
                     break;
                 }
-                retainAll |= (tag.text().indexOf("(retainAll)") != -1);
+                retainAll |= (tagText.indexOf("(retainAll)") != -1);
                 break;
 
             case PROVISIONAL:
@@ -411,14 +415,14 @@ public class CheckTags {
 
             case DEPRECATED:
                 foundDeprecatedTag = true;
-                if (tag.text().indexOf("ICU") == 0) {
+                if (tagText.indexOf("ICU") == 0) {
                     foundRequiredTag = true;
                 }
                 break;
 
             case OBSOLETE:
-                if (tag.text().indexOf("ICU") != 0) {
-                    tagErr(tag);
+                if (tagText.indexOf("ICU") != 0) {
+                    tagErr(doc, tag);
                 }
                 foundObsoleteTag = true;
                 foundRequiredTag = true;
@@ -426,9 +430,8 @@ public class CheckTags {
 
             case STABLE:
                 {
-                    String text = tag.text();
-                    if (text.length() != 0 && text.indexOf("ICU") != 0) {
-                        tagErr(tag);
+                    if (tagText.length() != 0 && tagText.indexOf("ICU") != 0) {
+                        tagErr(tagText, doc, tag);
                     }
                     foundRequiredTag = true;
                     foundStableTag = true;
@@ -436,11 +439,13 @@ public class CheckTags {
                 break;
 
             case SINCE:
-                tagErr(tag);
+                tagErr(doc, tag);
                 break;
 
             case EXCEPTION:
-                logln("You really ought to use @throws, you know... :-)");
+                //TODO: Why would we report this?
+                // logln("You really ought to use @throws, you know... :-)");
+                break;
 
             case AUTHOR:
             case SEE:
@@ -448,18 +453,20 @@ public class CheckTags {
             case RETURN:
             case THROWS:
             case SERIAL:
+            case DISCOURAGED:
+            case CATEGORY:
                 break;
 
             case VERSION:
-                tagErr(tag);
+                tagErr(doc, tag);
                 break;
 
             default:
                 errln("unknown index: " + ix);
-            }
-        }
+            } // end if switch
+        } // end of iteration on tags
         if (!foundRequiredTag) {
-            errln("missing required tag [" + doc.position() + "]");
+            errln("missing required tag [" + JavadocHelper.position(elements, docTrees, doc) + "]");
         }
         if (foundInternalTag && !foundDeprecatedTag) {
             errln("internal tag missing deprecated");
diff --git a/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/GatherAPIData.java b/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/GatherAPIData.java
index 47d249e08c5..afb8d911d5b 100644
--- a/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/GatherAPIData.java
+++ b/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/GatherAPIData.java
@@ -50,136 +50,96 @@ import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.io.OutputStreamWriter;
+import java.nio.charset.StandardCharsets;
 import java.util.Collection;
-import java.util.Iterator;
+import java.util.List;
+import java.util.Locale;
+import java.util.Set;
 import java.util.TreeSet;
 import java.util.regex.Pattern;
 import java.util.zip.GZIPOutputStream;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipOutputStream;
 
-import com.sun.javadoc.ClassDoc;
-import com.sun.javadoc.ConstructorDoc;
-import com.sun.javadoc.ExecutableMemberDoc;
-import com.sun.javadoc.FieldDoc;
-import com.sun.javadoc.LanguageVersion;
-import com.sun.javadoc.MemberDoc;
-import com.sun.javadoc.MethodDoc;
-import com.sun.javadoc.ProgramElementDoc;
-import com.sun.javadoc.RootDoc;
-import com.sun.javadoc.Tag;
+import javax.annotation.processing.SupportedAnnotationTypes;
+import javax.annotation.processing.SupportedSourceVersion;
+import javax.lang.model.SourceVersion;
+import javax.lang.model.element.Element;
+import javax.lang.model.element.ExecutableElement;
+import javax.lang.model.element.PackageElement;
+import javax.lang.model.element.TypeElement;
+import javax.lang.model.element.VariableElement;
+import javax.lang.model.type.ArrayType;
+import javax.lang.model.type.DeclaredType;
+import javax.lang.model.type.ErrorType;
+import javax.lang.model.type.ExecutableType;
+import javax.lang.model.type.IntersectionType;
+import javax.lang.model.type.NoType;
+import javax.lang.model.type.NullType;
+import javax.lang.model.type.PrimitiveType;
+import javax.lang.model.type.TypeMirror;
+import javax.lang.model.type.TypeVariable;
+import javax.lang.model.type.TypeVisitor;
+import javax.lang.model.type.UnionType;
+import javax.lang.model.type.WildcardType;
+import javax.lang.model.util.Elements;
 
-public class GatherAPIData {
-    RootDoc root;
-    TreeSet results;
-    String srcName = "Current"; // default source name
-    String output; // name of output file to write
-    String base; // strip this prefix
-    Pattern pat;
-    boolean zip;
-    boolean gzip;
-    boolean internal;
-    boolean version;
+import com.sun.source.doctree.BlockTagTree;
+import com.sun.source.util.DocTrees;
 
-    public static int optionLength(String option) {
-        if (option.equals("-name")) {
-            return 2;
-        } else if (option.equals("-output")) {
-            return 2;
-        } else if (option.equals("-base")) {
-            return 2;
-        } else if (option.equals("-filter")) {
-            return 2;
-        } else if (option.equals("-zip")) {
-            return 1;
-        } else if (option.equals("-gzip")) {
-            return 1;
-        } else if (option.equals("-internal")) {
-            return 1;
-        } else if (option.equals("-version")) {
-            return 1;
-        }
-        return 0;
+import jdk.javadoc.doclet.Doclet;
+import jdk.javadoc.doclet.DocletEnvironment;
+import jdk.javadoc.doclet.Reporter;
+
+@SupportedAnnotationTypes("*")
+@SupportedSourceVersion(SourceVersion.RELEASE_9)
+public class GatherAPIData implements Doclet {
+    private Elements elementUtils;
+    private DocTrees docTrees;
+    private TreeSet<APIInfo> results = new TreeSet<>(APIInfo.defaultComparator());
+    private String srcName = ""; // default source name
+    private String output; // name of output file to write
+    private String base; // strip this prefix
+    private Pattern pat;
+    private boolean zip;
+    private boolean gzip;
+    private boolean internal;
+    private boolean version;
+
+    @Override
+    public SourceVersion getSupportedSourceVersion() {
+        // The documentation says "usually the latest version"
+        // But even if at this time JDK 23 is already released, we
+        // want to be able to compile / use this doclet with at least JDK 11.
+        // So anything above RELEASE_11 is undefined
+        return SourceVersion.RELEASE_11;
     }
 
-    public static boolean start(RootDoc root) {
-        return new GatherAPIData(root).run();
+    @Override
+    public void init(Locale locale, Reporter reporter) {
     }
 
-    /**
-     * If you don't do this, javadoc treats enums like regular classes!
-     * doesn't matter if you pass -source 1.5 or not.
-     */
-    public static LanguageVersion languageVersion() {
-        return LanguageVersion.JAVA_1_5;
+    @Override
+    public String getName() {
+        return this.getClass().getSimpleName();
     }
 
-    GatherAPIData(RootDoc root) {
-        this.root = root;
-
-        String[][] options = root.options();
-        for (int i = 0; i < options.length; ++i) {
-            String opt = options[i][0];
-            if (opt.equals("-name")) {
-                this.srcName = options[i][1];
-            } else if (opt.equals("-output")) {
-                this.output = options[i][1];
-            } else if (opt.equals("-base")) {
-                this.base = options[i][1]; // should not include '.'
-            } else if (opt.equals("-filter")) {
-                this.pat = Pattern.compile(options[i][1], Pattern.CASE_INSENSITIVE);
-            } else if (opt.equals("-zip")) {
-                this.zip = true;
-            } else if (opt.equals("-gzip")) {
-                this.gzip = true;
-            } else if (opt.equals("-internal")) {
-                this.internal = true;
-            } else if (opt.equals("-version")) {
-                this.version = true;
-            }
-        }
-
-        results = new TreeSet(APIInfo.defaultComparator());
+    @Override
+    public Set<Doclet.Option> getSupportedOptions() {
+        return SUPPORTED_OPTIONS;
     }
 
-    private boolean run() {
-        doDocs(root.classes());
+    @Override
+    public boolean run(DocletEnvironment environment) {
+        elementUtils = environment.getElementUtils();
+        docTrees = environment.getDocTrees();
 
-        OutputStream os = System.out;
-        if (output != null) {
-            ZipOutputStream zos = null;
-            try {
-                if (zip) {
-                    zos = new ZipOutputStream(new FileOutputStream(output + ".zip"));
-                    zos.putNextEntry(new ZipEntry(output));
-                    os = zos;
-                } else if (gzip) {
-                    os = new GZIPOutputStream(new FileOutputStream(output + ".gz"));
-                } else {
-                    os = new FileOutputStream(output);
-                }
-            }
-            catch (IOException e) {
-                RuntimeException re = new RuntimeException(e.getMessage());
-                re.initCause(e);
-                throw re;
-            }
-            finally {
-                if (zos != null) {
-                    try {
-                        zos.close();
-                    } catch (Exception e) {
-                        // ignore
-                    }
-                }
-            }
-        }
-
-        BufferedWriter bw = null;
-        try {
-            OutputStreamWriter osw = new OutputStreamWriter(os, "UTF-8");
-            bw = new BufferedWriter(osw);
+        initFromOptions();
+        doDocs(environment.getIncludedElements());
 
+        try (OutputStream os = getOutputFileAsStream(output);
+                OutputStreamWriter osw = new OutputStreamWriter(os, StandardCharsets.UTF_8)) {
+            BufferedWriter bw = new BufferedWriter(osw);
             // writing data file
             bw.write(String.valueOf(APIInfo.VERSION) + APIInfo.SEP); // header version
             bw.write(srcName + APIInfo.SEP); // source name
@@ -188,35 +148,44 @@ public class GatherAPIData {
             writeResults(results, bw);
             bw.close(); // should flush, close all, etc
         } catch (IOException e) {
-            try { bw.close(); } catch (IOException e2) {}
-            RuntimeException re = new RuntimeException("write error: " + e.getMessage());
+            RuntimeException re = new RuntimeException(e.getMessage());
             re.initCause(e);
             throw re;
         }
 
-        return false;
+        return true;
     }
 
-    private void doDocs(ProgramElementDoc[] docs) {
-        if (docs != null && docs.length > 0) {
-            for (int i = 0; i < docs.length; ++i) {
-                doDoc(docs[i]);
+    private OutputStream getOutputFileAsStream(String output) throws IOException {
+        if (output == null) {
+            return System.out;
+        }
+        if (zip) {
+            ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(output + ".zip"));
+            zos.putNextEntry(new ZipEntry(output));
+            return zos;
+        }
+        if (gzip) {
+            return new GZIPOutputStream(new FileOutputStream(output + ".gz"));
+        }
+        return new FileOutputStream(output);
+    }
+
+    private void doDocs(Collection<? extends Element> docs) {
+        if (docs != null) {
+            for (Element doc : docs) {
+                doDoc(doc);
             }
         }
     }
 
-    private void doDoc(ProgramElementDoc doc) {
+    private void doDoc(Element doc) {
         if (ignore(doc)) return;
 
-        if (doc.isClass() || doc.isInterface()) {
-            ClassDoc cdoc = (ClassDoc)doc;
-            doDocs(cdoc.fields());
-            doDocs(cdoc.constructors());
-            doDocs(cdoc.methods());
-            doDocs(cdoc.enumConstants());
-            // don't call this to iterate over inner classes,
-            // root.classes already includes them
-            // doDocs(cdoc.innerClasses());
+        // isClass() ==> CLASS || ENUM;
+        // isInterface() ==> INTERFACE || ANNOTATION_TYPE
+        if (JavadocHelper.isKindClassOrInterface(doc)) {
+            doDocs(doc.getEnclosedElements());
         }
 
         APIInfo info = createInfo(doc);
@@ -225,28 +194,6 @@ public class GatherAPIData {
         }
     }
 
-    // Sigh. Javadoc doesn't indicate when the compiler generates
-    // the values and valueOf enum methods.  The position of the
-    // method for these is not always the same as the position of
-    // the class, though it often is, so we can't use that.
-
-    private boolean isIgnoredEnumMethod(ProgramElementDoc doc) {
-        if (doc.isMethod() && doc.containingClass().isEnum()) {
-            // System.out.println("*** " + doc.qualifiedName() + " pos: " +
-            //                    doc.position().line() +
-            //                    " contained by: " +
-            //                    doc.containingClass().name() +
-            //                    " pos: " +
-            //                    doc.containingClass().position().line());
-            // return doc.position().line() == doc.containingClass().position().line();
-
-            String name = doc.name();
-            // assume we don't have enums that overload these method names.
-            return "values".equals(name) || "valueOf".equals(name);
-        }
-        return false;
-    }
-
     // isSynthesized also doesn't seem to work.  Let's do this, documenting
     // synthesized constructors for abstract classes is kind of weird.
     // We can't actually tell if the constructor was synthesized or is
@@ -258,22 +205,38 @@ public class GatherAPIData {
     // javadoc comments by the policy. So, we no longer ignore abstract
     // class's no-arg constructor blindly. -Yoshito 2014-05-21
 
-    private boolean isAbstractClassDefaultConstructor(ProgramElementDoc doc) {
-        return doc.isConstructor()
-            && doc.containingClass().isAbstract()
-            && "()".equals(((ConstructorDoc) doc).signature());
+    private boolean isAbstractClassDefaultConstructor(Element doc) {
+        return JavadocHelper.isKindConstructor(doc)
+            && JavadocHelper.isAbstract(doc.getEnclosingElement())
+            && ((ExecutableElement) doc).getParameters().isEmpty();
     }
 
     private static final boolean IGNORE_NO_ARG_ABSTRACT_CTOR = false;
 
-    private boolean ignore(ProgramElementDoc doc) {
-        if (doc == null) return true;
-        if (doc.isPrivate() || doc.isPackagePrivate()) return true;
-        if (doc instanceof MemberDoc && ((MemberDoc)doc).isSynthetic()) return true;
-        if (doc.qualifiedName().indexOf(".misc") != -1) {
-            System.out.println("misc: " + doc.qualifiedName()); return true;
+    private boolean ignore(Element doc) {
+        if (doc == null) {
+            return true;
         }
-        if (isIgnoredEnumMethod(doc)) {
+
+        if (JavadocHelper.isPrivate(doc) || JavadocHelper.isDefault(doc)) {
+            return true;
+        }
+
+        if (JavadocHelper.isVisibilityPackage(doc)) {
+            return true;
+        }
+
+        if (JavadocHelper.isKindPackage(doc)) {
+            return true;
+        }
+
+        if (doc.toString().contains(".misc")) {
+            System.out.println("misc: " + doc.toString()); {
+                return true;
+            }
+        }
+
+        if (JavadocHelper.isIgnoredEnumMethod(doc)) {
             return true;
         }
 
@@ -281,66 +244,41 @@ public class GatherAPIData {
             return true;
         }
 
-        if (false && doc.qualifiedName().indexOf("LocaleDisplayNames") != -1) {
-          System.err.print("*** " + doc.qualifiedName() + ":");
-          if (doc.isClass()) System.err.print(" class");
-          if (doc.isConstructor()) System.err.print(" constructor");
-          if (doc.isEnum()) System.err.print(" enum");
-          if (doc.isEnumConstant()) System.err.print(" enum_constant");
-          if (doc.isError()) System.err.print(" error");
-          if (doc.isException()) System.err.print(" exception");
-          if (doc.isField()) System.err.print(" field");
-          if (doc.isInterface()) System.err.print(" interface");
-          if (doc.isMethod()) System.err.print(" method");
-          if (doc.isOrdinaryClass()) System.err.print(" ordinary_class");
-          System.err.println();
-        }
-
         if (!internal) { // debug
-            Tag[] tags = doc.tags();
-            for (int i = 0; i < tags.length; ++i) {
-                if (tagKindIndex(tags[i].kind()) == INTERNAL) { return true; }
+            for (BlockTagTree tag : JavadocHelper.getBlockTags(docTrees, doc)) {
+                if (JavadocHelper.TagKind.ofTag(tag) == JavadocHelper.TagKind.INTERNAL) {
+                    return true;
+                }
             }
         }
-        if (pat != null && (doc.isClass() || doc.isInterface())) {
-            if (!pat.matcher(doc.name()).matches()) {
+
+        if (pat != null && JavadocHelper.isKindClassOrInterface(doc)) {
+            if (!pat.matcher(doc.getSimpleName().toString()).matches()) {
                 return true;
             }
         }
+
         return false;
     }
 
-    private static void writeResults(Collection c, BufferedWriter w) {
-        Iterator iter = c.iterator();
-        while (iter.hasNext()) {
-            APIInfo info = (APIInfo)iter.next();
+    private static void writeResults(Collection<APIInfo> c, BufferedWriter w) {
+        for (APIInfo info : c) {
             info.writeln(w);
         }
     }
 
     private String trimBase(String arg) {
+        String orgArg = arg;
         if (base != null) {
             for (int n = arg.indexOf(base); n != -1; n = arg.indexOf(base, n)) {
-                arg = arg.substring(0, n) + arg.substring(n+base.length());
+                arg = arg.substring(0, n) + arg.substring(n + base.length());
             }
         }
         return arg;
     }
 
-    public APIInfo createInfo(ProgramElementDoc doc) {
-
-        // Doc. name
-        // Doc. isField, isMethod, isConstructor, isClass, isInterface
-        // ProgramElementDoc. containingClass, containingPackage
-        // ProgramElementDoc. isPublic, isProtected, isPrivate, isPackagePrivate
-        // ProgramElementDoc. isStatic, isFinal
-        // MemberDoc.isSynthetic
-        // ExecutableMemberDoc isSynchronized, signature
-        // Type.toString() // e.g. "String[][]"
-        // ClassDoc.isAbstract, superClass, interfaces, fields, methods, constructors, innerClasses
-        // FieldDoc type
-        // ConstructorDoc qualifiedName
-        // MethodDoc isAbstract, returnType
+    private APIInfo createInfo(Element doc) {
+        if (ignore(doc)) return null;
 
         APIInfo info = new APIInfo();
         if (version) {
@@ -353,128 +291,172 @@ public class GatherAPIData {
         info.setStatusVersion(version[0]);
 
         // visibility
-        if (doc.isPublic()) {
+        if (JavadocHelper.isPublic(doc)) {
             info.setPublic();
-        } else if (doc.isProtected()) {
+        } else if (JavadocHelper.isProtected(doc)) {
             info.setProtected();
-        } else if (doc.isPrivate()) {
+        } else if (JavadocHelper.isPrivate(doc)) {
             info.setPrivate();
         } else {
             // default is package
         }
 
         // static
-        if (doc.isStatic()) {
+        if (JavadocHelper.isStatic(doc)) {
             info.setStatic();
         } else {
             // default is non-static
         }
 
-        // final
-        if (doc.isFinal() && !doc.isEnum()) {
+        // Final. Enums are final by default.
+        if (JavadocHelper.isFinal(doc) && !JavadocHelper.isKindEnum(doc)) {
             info.setFinal();
         } else {
             // default is non-final
         }
 
         // type
-        if (doc.isField()) {
+        if (JavadocHelper.isKindFieldExact(doc)) {
             info.setField();
-        } else if (doc.isMethod()) {
+        } else if (JavadocHelper.isKindMethod(doc)) {
             info.setMethod();
-        } else if (doc.isConstructor()) {
+        } else if (JavadocHelper.isKindConstructor(doc)) {
             info.setConstructor();
-        } else if (doc.isClass() || doc.isInterface()) {
-            if (doc.isEnum()) {
+        } else if (JavadocHelper.isKindClassOrInterface(doc)) {
+            if (JavadocHelper.isKindEnum(doc)) {
                 info.setEnum();
             } else {
                 info.setClass();
             }
-        } else if (doc.isEnumConstant()) {
+        } else if (JavadocHelper.isKindEnumConstant(doc)) {
             info.setEnumConstant();
         }
 
-        info.setPackage(trimBase(doc.containingPackage().name()));
+        PackageElement packageElement = elementUtils.getPackageOf(doc);
+        info.setPackage(trimBase(packageElement.getQualifiedName().toString()));
 
-        String className = (doc.isClass() || doc.isInterface() || (doc.containingClass() == null))
+        String className = (JavadocHelper.isKindClassOrInterface(doc) || doc.getEnclosingElement() == null)
                 ? ""
-                : doc.containingClass().name();
+                : withoutPackage(doc.getEnclosingElement());
         info.setClassName(className);
 
-        String name = doc.name();
-        if (doc.isConstructor()) {
-            // Workaround for Javadoc incompatibility between 7 and 8.
-            // Javadoc 7 prepends enclosing class name for a nested
-            // class's constructor. We need to generate the same format
-            // because existing ICU API signature were generated with
-            // Javadoc 7 or older verions.
-            int dotIdx = className.lastIndexOf('.');
-            if (!name.contains(".") && dotIdx > 0) {
-                name = className.substring(0, dotIdx + 1) + name;
-            }
+        String name = doc.getSimpleName().toString();
+        if (JavadocHelper.isKindConstructor(doc)) {
+            // The constructor name is always `<init>` with the javax.lang APIs.
+            // For backward compatibility with older generated files we use the class name instead.
+            name = className;
+        } else if (JavadocHelper.isKindClassOrInterface(doc)) {
+            name = withoutPackage(doc);
         }
         info.setName(name);
 
-        if (doc instanceof FieldDoc) {
-            FieldDoc fdoc = (FieldDoc)doc;
-            info.setSignature(trimBase(fdoc.type().toString()));
-        } else if (doc instanceof ClassDoc) {
-            ClassDoc cdoc = (ClassDoc)doc;
+        if (JavadocHelper.isKindField(doc)) {
+            VariableElement fdoc = (VariableElement) doc;
+            hackSetSignature(info, trimBase(fdoc.asType().toString()));
+        } else if (JavadocHelper.isKindClassOrInterface(doc)) {
+            TypeElement cdoc = (TypeElement) doc;
 
-            if (cdoc.isClass() && cdoc.isAbstract()) {
+            if (!JavadocHelper.isKindInterface(doc) && JavadocHelper.isAbstract(cdoc)) {
                 // interfaces are abstract by default, don't mark them as abstract
                 info.setAbstract();
             }
 
             StringBuffer buf = new StringBuffer();
-            if (cdoc.isClass()) {
+            if (JavadocHelper.isKindClass(cdoc)) {
                 buf.append("extends ");
-                buf.append(cdoc.superclassType().toString());
+                buf.append(cdoc.getSuperclass().toString());
             }
-            ClassDoc[] imp = cdoc.interfaces();
-            if (imp != null && imp.length > 0) {
+            List<? extends TypeMirror> imp = cdoc.getInterfaces();
+            if (!imp.isEmpty()) {
                 if (buf.length() > 0) {
                     buf.append(" ");
                 }
                 buf.append("implements");
-                for (int i = 0; i < imp.length; ++i) {
+                for (int i = 0; i < imp.size(); ++i) {
                     if (i != 0) {
                         buf.append(",");
                     }
                     buf.append(" ");
-                    buf.append(imp[i].qualifiedName());
+                    buf.append(imp.get(i).toString()
+                            .replaceAll("<[^<>]+>", "") // interfaces with parameters.
+                            .replaceAll("<[^<>]+>", "") // 3 nesting levels should be enough
+                            .replaceAll("<[^<>]+>", "") // max I've seen was 2
+                    );
                 }
             }
-            info.setSignature(trimBase(buf.toString()));
-        } else {
-            ExecutableMemberDoc emdoc = (ExecutableMemberDoc)doc;
-            if (emdoc.isSynchronized()) {
+            hackSetSignature(info, trimBase(buf.toString()));
+        } else if (JavadocHelper.isKindMethod(doc) || JavadocHelper.isKindConstructor(doc)) {
+            ExecutableElement emdoc = (ExecutableElement)doc;
+            if (JavadocHelper.isSynchronized(emdoc)) {
                 info.setSynchronized();
             }
 
-            if (doc instanceof MethodDoc) {
-                MethodDoc mdoc = (MethodDoc)doc;
-                if (mdoc.isAbstract()) {
+            if (JavadocHelper.isKindMethod(doc)) {
+                if (JavadocHelper.isAbstract(emdoc)) {
                     // Workaround for Javadoc incompatibility between 7 and 8.
                     // isAbstract() returns false for a method in an interface
                     // on Javadoc 7, while Javadoc 8 returns true. Because existing
                     // API signature data files were generated before, we do not
                     // set abstract if a method is in an interface.
-                    if (!mdoc.containingClass().isInterface()) {
+                    if (!JavadocHelper.isKindInterface(emdoc.getEnclosingElement())) {
                         info.setAbstract();
                     }
                 }
-                info.setSignature(trimBase(mdoc.returnType().toString() + emdoc.signature()));
+
+                String retSig = stringFromTypeMirror(emdoc.getReturnType());
+
+                // Signature, as returned by default, can be something like this: "boolean<T>containsAll(java.util.Iterator<T>)"
+                // The old API returned "boolean(java.util.Iterator<T>)"
+                // Consider using the signature "as is" (including the method name)
+                hackSetSignature(info, trimBase(retSig + toTheBracket(emdoc.toString())));
             } else {
                 // constructor
-                info.setSignature(trimBase(emdoc.signature()));
+                hackSetSignature(info, toTheBracket(emdoc.toString()));
             }
+        } else {
+            throw new RuntimeException("Unknown element kind: " + doc.getKind());
         }
 
         return info;
     }
 
-    private int tagStatus(final ProgramElementDoc doc, String[] version) {
+    private static String stringFromTypeMirror(TypeMirror rrt) {
+        StringBuilder retSig = new StringBuilder();
+        rrt.accept(new ToStringTypeVisitor(), retSig);
+        return retSig.toString();
+    }
+
+    private void hackSetSignature(APIInfo info, String value) {
+        value = value.replace(",", ", ").replace(",  ", ", ");
+        info.setSignature(value);
+    }
+
+    private String withoutPackage(Element enclosingElement) {
+        if (enclosingElement == null) {
+            return "";
+        }
+
+        String result = enclosingElement.toString();
+
+        PackageElement pack = this.elementUtils.getPackageOf(enclosingElement);
+        if (pack == null) {
+            return result;
+        }
+
+        // Takes something like "com.ibm.icu.charset.CharsetCallback.Decoder"
+        // and removes the package, resulting in "CharsetCallback.Decoder"
+        // This can't really be done just by looking at the string form.
+        String packName = pack.getQualifiedName().toString() + ".";
+        return result.startsWith(packName) ? result.substring(packName.length()) : result;
+    }
+
+    private String toTheBracket(String str) {
+        if (str == null) return null;
+        int openBr = str.indexOf('(');
+        return openBr > 1 ? str.substring(openBr) : str;
+    }
+
+    private int tagStatus(final Element doc, String[] version) {
         class Result {
             boolean deprecatedFlag = false;
             int res = -1;
@@ -534,55 +516,54 @@ public class GatherAPIData {
             }
         }
 
-        Tag[] tags = doc.tags();
+        List<BlockTagTree> tags = JavadocHelper.getBlockTags(docTrees, doc);
         Result result = new Result();
         String statusVer = "";
-        for (int i = 0; i < tags.length; ++i) {
-            Tag tag = tags[i];
-
-            String kind = tag.kind();
-            int ix = tagKindIndex(kind);
+        for (BlockTagTree tag : tags) {
+            JavadocHelper.TagKind ix = JavadocHelper.TagKind.ofTag(tag);
 
             switch (ix) {
-            case INTERNAL:
-                result.set(internal ? APIInfo.STA_INTERNAL : -2); // -2 for legacy compatibility
-                statusVer = getStatusVersion(tag);
-                break;
+                case INTERNAL:
+                    result.set(internal ? APIInfo.STA_INTERNAL : -2); // -2 for legacy compatibility
+                    statusVer = getStatusVersion(tag);
+                    break;
 
-            case DRAFT:
-                result.set(APIInfo.STA_DRAFT);
-                statusVer = getStatusVersion(tag);
-                break;
+                case DRAFT:
+                    result.set(APIInfo.STA_DRAFT);
+                    statusVer = getStatusVersion(tag);
+                    break;
 
-            case STABLE:
-                result.set(APIInfo.STA_STABLE);
-                statusVer = getStatusVersion(tag);
-                break;
+                case STABLE:
+                    result.set(APIInfo.STA_STABLE);
+                    statusVer = getStatusVersion(tag);
+                    break;
 
-            case DEPRECATED:
-                result.set(APIInfo.STA_DEPRECATED);
-                statusVer = getStatusVersion(tag);
-                break;
+                case DEPRECATED:
+                    result.set(APIInfo.STA_DEPRECATED);
+                    statusVer = getStatusVersion(tag);
+                    break;
 
-            case OBSOLETE:
-                result.set(APIInfo.STA_OBSOLETE);
-                statusVer = getStatusVersion(tag);
-                break;
+                case OBSOLETE:
+                    result.set(APIInfo.STA_OBSOLETE);
+                    statusVer = getStatusVersion(tag);
+                    break;
 
-            case SINCE:
-            case EXCEPTION:
-            case VERSION:
-            case UNKNOWN:
-            case AUTHOR:
-            case SEE:
-            case PARAM:
-            case RETURN:
-            case THROWS:
-            case SERIAL:
-                break;
+                case SINCE:
+                case EXCEPTION:
+                case VERSION:
+                case UNKNOWN:
+                case AUTHOR:
+                case SEE:
+                case PARAM:
+                case RETURN:
+                case THROWS:
+                case SERIAL:
+                case DISCOURAGED:
+                case CATEGORY:
+                    break;
 
-            default:
-                throw new RuntimeException("unknown index " + ix + " for tag: " + kind);
+                default:
+                    throw new RuntimeException("unknown index " + ix + " for tag: " + tag);
             }
         }
 
@@ -592,8 +573,8 @@ public class GatherAPIData {
         return result.get();
     }
 
-    private String getStatusVersion(Tag tag) {
-        String text = tag.text();
+    private String getStatusVersion(BlockTagTree tag) {
+        String text = tag.toString();
         if (text != null && text.length() > 0) {
             // Extract version string
             int start = -1;
@@ -615,33 +596,128 @@ public class GatherAPIData {
         return "";
     }
 
-    private static final int UNKNOWN = -1;
-    private static final int INTERNAL = 0;
-    private static final int DRAFT = 1;
-    private static final int STABLE = 2;
-    private static final int SINCE = 3;
-    private static final int DEPRECATED = 4;
-    private static final int AUTHOR = 5;
-    private static final int SEE = 6;
-    private static final int VERSION = 7;
-    private static final int PARAM = 8;
-    private static final int RETURN = 9;
-    private static final int THROWS = 10;
-    private static final int OBSOLETE = 11;
-    private static final int EXCEPTION = 12;
-    private static final int SERIAL = 13;
+    private final static Set<Doclet.Option> SUPPORTED_OPTIONS = Set.of(
+        new JavadocHelper.GatherApiDataOption(1, "-name", "the_name", "the description of name"),
+        new JavadocHelper.GatherApiDataOption(1, "-output", "the_output", "the description of output"),
+        new JavadocHelper.GatherApiDataOption(1, "-base", "the_base", "the description of base"),
+        new JavadocHelper.GatherApiDataOption(1, "--filter", "the_filter", "the description of filter"),
+        new JavadocHelper.GatherApiDataOption(0, "-zip", "the description of zip"),
+        new JavadocHelper.GatherApiDataOption(0, "-gzip", "the description of gzip"),
+        new JavadocHelper.GatherApiDataOption(0, "-internal", "the description of internal"),
+        new JavadocHelper.GatherApiDataOption(0, "-version", "the description of version")
+    );
 
-    private static int tagKindIndex(String kind) {
-        final String[] tagKinds = {
-            "@internal", "@draft", "@stable", "@since", "@deprecated", "@author", "@see",
-            "@version", "@param", "@return", "@throws", "@obsolete", "@exception", "@serial"
-        };
-
-        for (int i = 0; i < tagKinds.length; ++i) {
-            if (kind.equals(tagKinds[i])) {
-                return i;
+    private void initFromOptions() {
+        for (Doclet.Option opt : SUPPORTED_OPTIONS) {
+            JavadocHelper.GatherApiDataOption option = (JavadocHelper.GatherApiDataOption) opt;
+            switch (option.getName()) {
+                case "-name":
+                    this.srcName = option.getStringValue("");
+                    break;
+                case "-output":
+                    this.output = option.getStringValue(null);
+                    break;
+                case "-base":
+                    this.base = option.getStringValue(null); // should not include '.'
+                    break;
+                case "-filter":
+                    String filt = option.getStringValue(null);
+                    if (filt != null) {
+                        this.pat = Pattern.compile(filt, Pattern.CASE_INSENSITIVE);
+                    }
+                    break;
+                case "-zip":
+                    this.zip = option.getBooleanValue(false);
+                    break;
+                case "-gzip":
+                    this.gzip = option.getBooleanValue(false);
+                    break;
+                case "-internal":
+                    this.internal = option.getBooleanValue(false);
+                    break;
+                case "-version":
+                    this.version = option.getBooleanValue(false);
+                    break;
             }
         }
-        return UNKNOWN;
     }
+
+    static class ToStringTypeVisitor implements TypeVisitor<StringBuilder, StringBuilder> {
+
+        @Override
+        public StringBuilder visitPrimitive(PrimitiveType t, StringBuilder p) {
+            return p.append(t);
+        }
+
+        @Override
+        public StringBuilder visitArray(ArrayType t, StringBuilder p) {
+            return p.append(t);
+        }
+
+        @Override
+        public StringBuilder visitDeclared(DeclaredType t, StringBuilder p) {
+            return p.append(t);
+        }
+
+        @Override
+        public StringBuilder visitTypeVariable(TypeVariable t, StringBuilder p) {
+            String upperBound = t.getUpperBound().toString();
+            p.append(t.asElement().getSimpleName());
+            if (!"java.lang.Object".equals(upperBound)) {
+                return p.append(" extends ").append(upperBound);
+            }
+            return p;
+        }
+
+        @Override
+        public StringBuilder visitNoType(NoType t, StringBuilder p) {
+            return p.append(t);
+        }
+
+        // ==================================================================
+        // Below this line there are unexpected types.
+        // But we must implement them because the interface requires it.
+        // And also because we want to throw (so that we can fix it).
+
+        @Override
+        public StringBuilder visitNull(NullType t, StringBuilder p) {
+            throw new RuntimeException("Unexpected visitor NullType:" + t);
+        }
+
+        @Override
+        public StringBuilder visitUnknown(TypeMirror t, StringBuilder p) {
+            throw new RuntimeException("Unexpected visitor TypeMirror:" + t);
+        }
+
+        @Override
+        public StringBuilder visitUnion(UnionType t, StringBuilder p) {
+            throw new RuntimeException("Unexpected visitor UnionType:" + t);
+        }
+
+        @Override
+        public StringBuilder visit(TypeMirror t, StringBuilder p) {
+            throw new RuntimeException("Unexpected visitor TypeMirror:" + t);
+        }
+
+        @Override
+        public StringBuilder visitIntersection(IntersectionType t, StringBuilder p) {
+            throw new RuntimeException("Unexpected visitor IntersectionType:" + t);
+        }
+
+        @Override
+        public StringBuilder visitWildcard(WildcardType t, StringBuilder p) {
+            throw new RuntimeException("Unexpected visitor WildcardType:" + t);
+        }
+
+        @Override
+        public StringBuilder visitExecutable(ExecutableType t, StringBuilder p) {
+            throw new RuntimeException("Unexpected visitor ExecutableType:" + t);
+        }
+
+        @Override
+        public StringBuilder visitError(ErrorType t, StringBuilder p) {
+            throw new RuntimeException("Unexpected visitor ErrorType:" + t);
+        }
+    }
+
 }
diff --git a/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/GatherAPIDataOld.java b/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/GatherAPIDataOld.java
deleted file mode 100644
index 2da1975aaab..00000000000
--- a/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/GatherAPIDataOld.java
+++ /dev/null
@@ -1,509 +0,0 @@
-// © 2016 and later: Unicode, Inc. and others.
-// License & terms of use: http://www.unicode.org/copyright.html
-/**
- *******************************************************************************
- * Copyright (C) 2004-2012, International Business Machines Corporation and    *
- * others. All Rights Reserved.                                                *
- *******************************************************************************
- */
-
-/**
- * Generate a list of ICU's public APIs, sorted by qualified name and signature
- * public APIs are all non-internal, non-package apis in com.ibm.icu.[lang|math|text|util].
- * For each API, list
- * - public, package, protected, or private (PB PK PT PR)
- * - static or non-static (STK NST)
- * - final or non-final (FN NF)
- * - synchronized or non-synchronized (SYN NSY)
- * - stable, draft, deprecated, obsolete (ST DR DP OB)
- * - abstract or non-abstract (AB NA)
- * - constructor, member, field (C M F)
- *
- * Requires JDK 1.4.2 or later
- * 
- * Sample compilation:
- * c:/doug/java/jdk1.4.2/build/windows-i586/bin/javac *.java
- *
- * Sample execution
- * c:/j2sdk1.4.2/bin/javadoc
- *   -classpath c:/jd2sk1.4.2/lib/tools.jar 
- *   -doclet com.ibm.icu.dev.tool.docs.GatherAPIData
- *   -docletpath c:/doug/cvsproj/icu4j/src 
- *   -sourcepath c:/doug/cvsproj/icu4j/src 
- *   -name "ICU4J 3.0"
- *   -output icu4j30.api
- *   -gzip
- *   -source 1.4
- *   com.ibm.icu.lang com.ibm.icu.math com.ibm.icu.text com.ibm.icu.util
- *
- * todo: provide command-line control of filters of which subclasses/packages to process
- * todo: record full inheritance hierarchy, not just immediate inheritance 
- * todo: allow for aliasing comparisons (force (pkg.)*class to be treated as though it 
- *       were in a different pkg/class hierarchy (facilitates comparison of icu4j and java)
- */
-
-package com.ibm.icu.dev.tool.docs;
-
-// standard release sdk won't work, need internal build to get access to javadoc
-import java.io.BufferedWriter;
-import java.io.FileOutputStream;
-import java.io.IOException;
-import java.io.OutputStream;
-import java.io.OutputStreamWriter;
-import java.util.Collection;
-import java.util.Iterator;
-import java.util.TreeSet;
-import java.util.regex.Pattern;
-import java.util.zip.GZIPOutputStream;
-import java.util.zip.ZipEntry;
-import java.util.zip.ZipOutputStream;
-
-import com.sun.javadoc.ClassDoc;
-import com.sun.javadoc.ConstructorDoc;
-import com.sun.javadoc.Doc;
-import com.sun.javadoc.ExecutableMemberDoc;
-import com.sun.javadoc.FieldDoc;
-import com.sun.javadoc.MethodDoc;
-import com.sun.javadoc.ProgramElementDoc;
-import com.sun.javadoc.RootDoc;
-import com.sun.javadoc.Tag;
-
-public class GatherAPIDataOld {
-    RootDoc root;
-    TreeSet results;
-    String srcName = "Current"; // default source name
-    String output; // name of output file to write
-    String base; // strip this prefix
-    Pattern pat;
-    boolean zip;
-    boolean gzip;
-    boolean internal;
-    boolean version;
-
-    public static int optionLength(String option) {
-        if (option.equals("-name")) {
-            return 2;
-        } else if (option.equals("-output")) {
-            return 2;
-        } else if (option.equals("-base")) {
-            return 2;
-        } else if (option.equals("-filter")) {
-            return 2;
-        } else if (option.equals("-zip")) {
-            return 1;
-        } else if (option.equals("-gzip")) {
-            return 1;
-        } else if (option.equals("-internal")) {
-            return 1;
-        } else if (option.equals("-version")) {
-            return 1;
-        }
-        return 0;
-    }
-
-    public static boolean start(RootDoc root) {
-        return new GatherAPIDataOld(root).run();
-    }
-
-    GatherAPIDataOld(RootDoc root) {
-        this.root = root;
-
-        String[][] options = root.options();
-        for (int i = 0; i < options.length; ++i) {
-            String opt = options[i][0];
-            if (opt.equals("-name")) {
-                this.srcName = options[i][1];
-            } else if (opt.equals("-output")) {
-                this.output = options[i][1];
-            } else if (opt.equals("-base")) {
-                this.base = options[i][1]; // should not include '.'
-            } else if (opt.equals("-filter")) {
-                this.pat = Pattern.compile(options[i][1], Pattern.CASE_INSENSITIVE);
-            } else if (opt.equals("-zip")) {
-                this.zip = true;
-            } else if (opt.equals("-gzip")) {
-                this.gzip = true;
-            } else if (opt.equals("-internal")) {
-                this.internal = true;
-            } else if (opt.equals("-version")) {
-                this.version = true;
-            }
-        }
-
-        results = new TreeSet(APIInfo.defaultComparator());
-    }
-
-    private boolean run() {
-        doDocs(root.classes());
-
-        OutputStream os = System.out;
-        if (output != null) {
-            ZipOutputStream zos = null;
-            try {
-                if (zip) {
-                    zos = new ZipOutputStream(new FileOutputStream(output + ".zip"));
-                    zos.putNextEntry(new ZipEntry(output));
-                    os = zos;
-                } else if (gzip) {
-                    os = new GZIPOutputStream(new FileOutputStream(output + ".gz"));
-                } else {
-                    os = new FileOutputStream(output);
-                }
-            }
-            catch (IOException e) {
-                RuntimeException re = new RuntimeException(e.getMessage());
-                re.initCause(e);
-                throw re;
-            }
-            finally {
-                if (zos != null) {
-                    try {
-                        zos.close();
-                    } catch (Exception e) {
-                        // ignore
-                    }
-                }
-            }
-        }
-
-        BufferedWriter bw = null;
-        try {
-            OutputStreamWriter osw = new OutputStreamWriter(os, "UTF-8");
-            bw = new BufferedWriter(osw);
-
-            // writing data file
-            bw.write(String.valueOf(APIInfo.VERSION) + APIInfo.SEP); // header version
-            bw.write(srcName + APIInfo.SEP); // source name
-            bw.write((base == null ? "" : base) + APIInfo.SEP); // base
-            bw.newLine();
-            writeResults(results, bw);
-            bw.close(); // should flush, close all, etc
-        } catch (IOException e) {
-            try { bw.close(); } catch (IOException e2) {}
-            RuntimeException re = new RuntimeException("write error: " + e.getMessage());
-            re.initCause(e);
-            throw re;
-        }
-
-        return false;
-    }
-
-    private void doDocs(ProgramElementDoc[] docs) {
-        if (docs != null && docs.length > 0) {
-            for (int i = 0; i < docs.length; ++i) {
-                doDoc(docs[i]);
-            }
-        }
-    }
-
-    private void doDoc(ProgramElementDoc doc) {
-        if (ignore(doc)) return;
-
-        if (doc.isClass() || doc.isInterface()) {
-            ClassDoc cdoc = (ClassDoc)doc;
-            doDocs(cdoc.fields());
-            doDocs(cdoc.constructors());
-            doDocs(cdoc.methods());
-            doDocs(cdoc.innerClasses());
-        }
-
-        APIInfo info = createInfo(doc);
-        if (info != null) {
-            results.add(info);
-        }
-    }
-
-    private boolean ignore(ProgramElementDoc doc) {
-        if (doc == null) return true;
-        if (doc.isPrivate() || doc.isPackagePrivate()) return true;
-        if (doc instanceof ConstructorDoc && ((ConstructorDoc)doc).isSynthetic()) return true;
-        if (doc.qualifiedName().indexOf(".misc") != -1) { 
-            System.out.println("misc: " + doc.qualifiedName()); return true; 
-        }
-        if (!internal) { // debug
-            Tag[] tags = doc.tags();
-            for (int i = 0; i < tags.length; ++i) {
-                if (tagKindIndex(tags[i].kind()) == INTERNAL) { return true; }
-            }
-        }
-        if (pat != null && (doc.isClass() || doc.isInterface())) {
-            if (!pat.matcher(doc.name()).matches()) {
-                return true;
-            }
-        }
-        return false;
-    }
-
-    private static void writeResults(Collection c, BufferedWriter w) {
-        Iterator iter = c.iterator();
-        while (iter.hasNext()) {
-            APIInfo info = (APIInfo)iter.next();
-            info.writeln(w);
-        }
-    }
-
-    private String trimBase(String arg) {
-        if (base != null) {
-            for (int n = arg.indexOf(base); n != -1; n = arg.indexOf(base, n)) {
-                arg = arg.substring(0, n) + arg.substring(n+base.length());
-            }
-        }
-        return arg;
-    }
-
-    public APIInfo createInfo(ProgramElementDoc doc) {
-
-        // Doc. name
-        // Doc. isField, isMethod, isConstructor, isClass, isInterface
-        // ProgramElementDoc. containingClass, containingPackage
-        // ProgramElementDoc. isPublic, isProtected, isPrivate, isPackagePrivate
-        // ProgramElementDoc. isStatic, isFinal
-        // MemberDoc.isSynthetic
-        // ExecutableMemberDoc isSynchronized, signature
-        // Type.toString() // e.g. "String[][]"
-        // ClassDoc.isAbstract, superClass, interfaces, fields, methods, constructors, innerClasses
-        // FieldDoc type
-        // ConstructorDoc qualifiedName
-        // MethodDoc isAbstract, returnType
-
-        APIInfo info = new APIInfo();
-        if (version) {
-            info.includeStatusVersion(true);
-        }
-            
-        // status
-        String[] version = new String[1];
-        info.setType(APIInfo.STA, tagStatus(doc, version));
-        info.setStatusVersion(version[0]);
-
-        // visibility
-        if (doc.isPublic()) {
-            info.setPublic();
-        } else if (doc.isProtected()) {
-            info.setProtected();
-        } else if (doc.isPrivate()) {
-            info.setPrivate();
-        } else {
-            // default is package
-        }
-
-        // static
-        if (doc.isStatic()) {
-            info.setStatic();
-        } else {
-            // default is non-static
-        }
-
-        // final
-        if (doc.isFinal()) {
-            info.setFinal();
-        } else {
-            // default is non-final
-        }
-
-        // type
-        if (doc.isField()) {
-            info.setField();
-        } else if (doc.isMethod()) {
-            info.setMethod();
-        } else if (doc.isConstructor()) {
-            info.setConstructor();
-        } else if (doc.isClass() || doc.isInterface()) {
-            info.setClass();
-        }
-
-        info.setPackage(trimBase(doc.containingPackage().name()));
-        info.setClassName((doc.isClass() || doc.isInterface() || (doc.containingClass() == null)) 
-                          ? "" 
-                          : trimBase(doc.containingClass().name()));
-        info.setName(trimBase(doc.name()));
-
-        if (doc instanceof FieldDoc) {
-            FieldDoc fdoc = (FieldDoc)doc;
-            info.setSignature(trimBase(fdoc.type().toString()));
-        } else if (doc instanceof ClassDoc) {
-            ClassDoc cdoc = (ClassDoc)doc;
-
-            if (cdoc.isClass() && cdoc.isAbstract()) { 
-                // interfaces are abstract by default, don't mark them as abstract
-                info.setAbstract();
-            }
-
-            StringBuffer buf = new StringBuffer();
-            if (cdoc.isClass()) {
-                buf.append("extends ");
-                buf.append(cdoc.superclass().qualifiedName());
-            }
-            ClassDoc[] imp = cdoc.interfaces();
-            if (imp != null && imp.length > 0) {
-                if (buf.length() > 0) {
-                    buf.append(" ");
-                }
-                buf.append("implements");
-                for (int i = 0; i < imp.length; ++i) {
-                    if (i != 0) {
-                        buf.append(",");
-                    }
-                    buf.append(" ");
-                    buf.append(imp[i].qualifiedName());
-                }
-            }
-            info.setSignature(trimBase(buf.toString()));
-        } else {
-            ExecutableMemberDoc emdoc = (ExecutableMemberDoc)doc;
-            if (emdoc.isSynchronized()) {
-                info.setSynchronized();
-            }
-
-            if (doc instanceof MethodDoc) {
-                MethodDoc mdoc = (MethodDoc)doc;
-                if (mdoc.isAbstract()) {
-                    info.setAbstract();
-                }
-                info.setSignature(trimBase(mdoc.returnType().toString() + emdoc.signature()));
-            } else {
-                // constructor
-                info.setSignature(trimBase(emdoc.signature()));
-            }
-        }
-
-        return info;
-    }
-
-    private int tagStatus(final Doc doc, String[] version) {
-        class Result {
-            int res = -1;
-            void set(int val) { 
-                if (res != -1) {
-                    if (val == APIInfo.STA_DEPRECATED) {
-                        // ok to have both a 'standard' tag and deprecated
-                        return;
-                    } else if (res != APIInfo.STA_DEPRECATED) {
-                        // if already not deprecated, this is an error
-                        System.err.println("bad doc: " + doc + " both: " + APIInfo.getTypeValName(APIInfo.STA, res) + " and: " + APIInfo.getTypeValName(APIInfo.STA, val)); 
-                        return;
-                    }
-                }
-                // ok to replace with new tag
-                res = val;
-            }
-            int get() {
-                if (res == -1) {
-                    System.err.println("warning: no tag for " + doc);
-                    return 0;
-                }
-                return res;
-            }
-        }
-
-        Tag[] tags = doc.tags();
-        Result result = new Result();
-        String statusVer = "";
-        for (int i = 0; i < tags.length; ++i) {
-            Tag tag = tags[i];
-
-            String kind = tag.kind();
-            int ix = tagKindIndex(kind);
-
-            switch (ix) {
-            case INTERNAL:
-                result.set(internal ? APIInfo.STA_INTERNAL : -2); // -2 for legacy compatibility
-                statusVer = getStatusVersion(tag);
-                break;
-
-            case DRAFT:
-                result.set(APIInfo.STA_DRAFT);
-                statusVer = getStatusVersion(tag);
-                break;
-
-            case STABLE:
-                result.set(APIInfo.STA_STABLE);
-                statusVer = getStatusVersion(tag);
-                break;
-
-            case DEPRECATED:
-                result.set(APIInfo.STA_DEPRECATED);
-                statusVer = getStatusVersion(tag);
-                break;
-
-            case OBSOLETE:
-                result.set(APIInfo.STA_OBSOLETE);
-                statusVer = getStatusVersion(tag);
-                break;
-
-            case SINCE:
-            case EXCEPTION:
-            case VERSION:
-            case UNKNOWN:
-            case AUTHOR:
-            case SEE:
-            case PARAM:
-            case RETURN:
-            case THROWS:
-            case SERIAL:
-                break;
-
-            default:
-                throw new RuntimeException("unknown index " + ix + " for tag: " + kind);
-            }
-        }
-
-        if (version != null) {
-            version[0] = statusVer;
-        }
-        return result.get();
-    }
-
-    private String getStatusVersion(Tag tag) {
-        String text = tag.text();
-        if (text != null && text.length() > 0) {
-            // Extract version string
-            int start = -1;
-            int i = 0;
-            for (; i < text.length(); i++) {
-                char ch = text.charAt(i);
-                if (ch == '.' || (ch >= '0' && ch <= '9')) {
-                    if (start == -1) {
-                        start = i;
-                    }
-                } else if (start != -1) {
-                    break;
-                }
-            }
-            if (start != -1) {
-                return text.substring(start, i);
-            }
-        }
-        return "";
-    }
-
-    private static final int UNKNOWN = -1;
-    private static final int INTERNAL = 0;
-    private static final int DRAFT = 1;
-    private static final int STABLE = 2;
-    private static final int SINCE = 3;
-    private static final int DEPRECATED = 4;
-    private static final int AUTHOR = 5;
-    private static final int SEE = 6;
-    private static final int VERSION = 7;
-    private static final int PARAM = 8;
-    private static final int RETURN = 9;
-    private static final int THROWS = 10;
-    private static final int OBSOLETE = 11;
-    private static final int EXCEPTION = 12;
-    private static final int SERIAL = 13;
-
-    private static int tagKindIndex(String kind) {
-        final String[] tagKinds = {
-            "@internal", "@draft", "@stable", "@since", "@deprecated", "@author", "@see", "@version",
-            "@param", "@return", "@throws", "@obsolete", "@exception", "@serial"
-        };
-
-        for (int i = 0; i < tagKinds.length; ++i) {
-            if (kind.equals(tagKinds[i])) {
-                return i;
-            }
-        }
-        return UNKNOWN;
-    }
-}
diff --git a/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/JavadocHelper.java b/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/JavadocHelper.java
new file mode 100644
index 00000000000..a128ce6e521
--- /dev/null
+++ b/icu4j/tools/build/src/main/java/com/ibm/icu/dev/tool/docs/JavadocHelper.java
@@ -0,0 +1,383 @@
+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/**
+*******************************************************************************
+* Copyright (C) 2002-2010, International Business Machines Corporation and    *
+* others. All Rights Reserved.                                                *
+*******************************************************************************
+*/
+/**
+ * This is a tool to check the tags on ICU4J files.  In particular, we're looking for:
+ *
+ * - methods that have no tags
+ * - custom tags: @draft, @stable, @internal?
+ * - standard tags: @since, @deprecated
+ *
+ * Syntax of tags:
+ * '@draft ICU X.X.X'
+ * '@stable ICU X.X.X'
+ * '@internal'
+ * '@since  (don't use)'
+ * '@obsolete ICU X.X.X'
+ * '@deprecated to be removed in ICU X.X. [Use ...]'
+ *
+ * flags names of classes and their members that have no tags or incorrect syntax.
+ *
+ * Requires JDK 1.4 or later
+ *
+ * Use build.xml 'checktags' ant target, or
+ * run from directory containing CheckTags.class as follows:
+ * javadoc -classpath ${JAVA_HOME}/lib/tools.jar -doclet CheckTags -sourcepath ${ICU4J_src} [packagenames]
+ */
+
+package com.ibm.icu.dev.tool.docs;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+
+import javax.lang.model.element.Element;
+import javax.lang.model.element.ElementKind;
+import javax.lang.model.element.Modifier;
+import javax.lang.model.util.Elements;
+
+import com.sun.source.doctree.BlockTagTree;
+import com.sun.source.doctree.InlineTagTree;
+import com.sun.source.doctree.DocCommentTree;
+import com.sun.source.doctree.DocTree;
+import com.sun.source.tree.CompilationUnitTree;
+import com.sun.source.util.DocTrees;
+import com.sun.source.util.TreePath;
+
+import jdk.javadoc.doclet.Doclet;
+
+class JavadocHelper {
+    // ===== Kind =====
+
+    /** The standard {@code isClass()} test returns true for both {@code CLASS}
+     * and {@code ENUM}.
+     * If what you need is CLASS only, use {@link #isKindClassExact(Element element)}@
+     */
+    static boolean isKindClass(Element element) {
+        return element.getKind().isClass();
+    }
+
+    static boolean isKindClassExact(Element element) {
+        return element.getKind() == ElementKind.CLASS;
+    }
+
+    /** The standard {@code isInterface()} test returns true for both {@code INTERFACE}
+     * and {@code ANNOTATION_TYPE}.
+     * If what you need is INTERFACE only, use {@link #isKindInterfaceExact(Element element)}@
+     */
+    static boolean isKindInterface(Element element) {
+        return element.getKind().isInterface();
+    }
+
+    static boolean isKindInterfaceExact(Element element) {
+        return element.getKind() == ElementKind.INTERFACE;
+    }
+
+    static boolean isKindConstructor(Element element) {
+        return element.getKind() == ElementKind.CONSTRUCTOR;
+    }
+
+    static boolean isKindMethod(Element element) {
+        return element.getKind() == ElementKind.METHOD;
+    }
+
+    static boolean isKindEnum(Element element) {
+        return element.getKind() == ElementKind.ENUM;
+    }
+
+    /** The standard {@code isField()} test returns true for both {@code FIELD}
+     * and {@code ENUM_CONSTANT}.
+     * If what you need is FIELD only, use {@link #isKindFieldExact(Element element)}@
+     */
+    static boolean isKindField(Element element) {
+        return element.getKind().isField();
+    }
+
+    static boolean isKindFieldExact(Element element) {
+        return element.getKind() == ElementKind.FIELD;
+    }
+
+    static boolean isKindEnumConstant(Element element) {
+        return element.getKind() == ElementKind.ENUM_CONSTANT;
+    }
+
+    static boolean isKindPackage(Element element) {
+        return element.getKind() == ElementKind.PACKAGE;
+    }
+
+    static boolean isKindClassOrInterface(Element element) {
+        ElementKind kind = element.getKind();
+        return kind.isClass() || kind.isInterface();
+    }
+
+    // Visibility
+    static boolean isPublic(Element element) {
+        return element.getModifiers().contains(Modifier.PUBLIC);
+    }
+
+    static boolean isProtected(Element element) {
+        return element.getModifiers().contains(Modifier.PROTECTED);
+    }
+
+    static boolean isPrivate(Element element) {
+        return element.getModifiers().contains(Modifier.PRIVATE);
+    }
+
+    static boolean isAbstract(Element element) {
+        return element.getModifiers().contains(Modifier.ABSTRACT);
+    }
+
+    static boolean isStatic(Element element) {
+        return element.getModifiers().contains(Modifier.STATIC);
+    }
+
+    static boolean isFinal(Element element) {
+        return element.getModifiers().contains(Modifier.FINAL);
+    }
+
+    static boolean isDefault(Element element) {
+        return element.getModifiers().contains(Modifier.DEFAULT);
+    }
+
+    static boolean isSynchronized(Element element) {
+        return element.getModifiers().contains(Modifier.SYNCHRONIZED);
+    }
+
+    static boolean isVisibilityPackage(Element element) {
+        Set<Modifier> modifiers = element.getModifiers();
+        if (modifiers.contains(Modifier.PUBLIC)
+                || modifiers.contains(Modifier.PROTECTED)
+                || modifiers.contains(Modifier.PRIVATE)) {
+            return false;
+        }
+        return true;
+    }
+
+    static boolean isSynthetic(Elements elements, Element element) {
+        return elements.getOrigin(element) == Elements.Origin.SYNTHETIC;
+    }
+
+    static String flatSignature(Element element) {
+        return element == null ? "null" : element.toString().replace("java.lang.", "");
+    }
+
+    /** Returns the location of the element, in the /absolute/path/to/File.java[1234] form. */
+    static String position(Elements el, DocTrees docTrees, Element element) {
+        TreePath path = docTrees.getPath(element);
+        if (path == null) {
+            // I've seen this happening for values() and valueOf(), which are created by the compiler
+            // in enums. So they "exist", but there is no location in the file for them.
+            // After ignoring values() and valueOf() (we can't tag them anyway), this error never happens.
+            // But let's keep it here, for future safety. Who knows what else the compiler will start creating.
+            return "<unknown_location>:<unknown_line>";
+        }
+        CompilationUnitTree cu = path.getCompilationUnit();
+        long startPos = docTrees.getSourcePositions().getStartPosition(cu, docTrees.getTree(element));
+        return cu.getSourceFile().getName() + ":" + cu.getLineMap().getLineNumber(startPos);
+    }
+
+    static String position(Elements el, DocTrees docTrees, Element element, DocTree tag) {
+        // I didn't manage to get the location of a tag, but at least we can show the location
+        // of the parent element.
+        return position(el, docTrees, element);
+    }
+
+    static List<BlockTagTree> getBlockTags(DocTrees docTrees, Element element) {
+        List<BlockTagTree> result = new ArrayList<>();
+        DocCommentTree dct = docTrees.getDocCommentTree(element);
+        if (dct == null) {
+            return result;
+        }
+        List<? extends DocTree> blockTags = dct.getBlockTags();
+        if (blockTags == null) {
+            return result;
+        }
+        for (DocTree btags : blockTags) {
+            result.add((BlockTagTree) btags);
+        }
+        return result;
+    }
+
+    static List<InlineTagTree> getInnerTags(DocTrees docTrees, Element element) {
+        List<InlineTagTree> result = new ArrayList<>();
+        DocCommentTree dct = docTrees.getDocCommentTree(element);
+        if (dct == null) {
+            return result;
+        }
+        List<? extends DocTree> fullBody = dct.getFullBody();
+        if (fullBody == null) {
+            return result;
+        }
+        for (DocTree tag : fullBody) {
+            if (tag instanceof InlineTagTree) {
+                result.add((InlineTagTree) tag);
+            }
+        }
+        return result;
+    }
+
+    static String toText(DocTree dt) {
+        String result = dt == null ? "<null>" : dt.toString();
+        if (result.startsWith("{@") && result.endsWith("}")) {
+            // Remove the `{` and `}` from an inline tag (`{@foo some text here}`)
+            result = result.substring(1, result.length() - 1);
+        }
+        // Remove the `@foo` part of the tag, applies to the block tags, and the inline tag cleaned above
+        if (result.startsWith("@")) {
+            result = result.replaceFirst("^@[a-zA-Z0-9_]+\\s+", "");
+        }
+        return result;
+    }
+
+    // Sigh. Javadoc doesn't indicate when the compiler generates
+    // the values and valueOf enum methods.  The position of the
+    // method for these is not always the same as the position of
+    // the class, though it often is, so we can't use that.
+    static boolean isIgnoredEnumMethod(Element doc) {
+        if (JavadocHelper.isKindMethod(doc) && JavadocHelper.isKindEnum(doc.getEnclosingElement())) {
+            String name = doc.getSimpleName().toString();
+            // assume we don't have enums that overload these method names.
+            return "values".equals(name) || "valueOf".equals(name);
+        }
+        return false;
+    }
+
+    // Doclet options
+    static class GatherApiDataOption implements Doclet.Option {
+        final int length;
+        final String name;
+        final String paramName;
+        final String description;
+        String strValue = null;
+        Boolean boolValue = null;
+
+        GatherApiDataOption(int length, String name, String description) {
+            this(length, name, null, description); // no parameter
+        }
+
+        GatherApiDataOption(int length, String name, String paramName, String description) {
+            this.length = length;
+            this.name = name;
+            this.paramName = paramName;
+            this.description = description;
+        }
+
+        @Override
+        public int getArgumentCount() {
+            return length;
+        }
+
+        @Override
+        public String getDescription() {
+            return description;
+        }
+
+        @Override
+        public Doclet.Option.Kind getKind() {
+            return Doclet.Option.Kind.STANDARD;
+        }
+
+        @Override
+        public List<String> getNames() {
+            return List.of(name);
+        }
+
+        @Override
+        public String getParameters() {
+            return this.paramName;
+        }
+
+        @Override
+        public boolean process(String option, List<String> arguments) {
+            if (!option.equals(name)) {
+                return false;
+            }
+            if (length == 0) {
+                boolValue = true;
+                return true;
+            }
+            if (arguments == null || arguments.size() < 1) {
+                return false;
+            }
+            strValue = arguments.get(0);
+            return true;
+        }
+
+        public String getName() {
+            return name;
+        }
+
+        public Boolean getBooleanValue(Boolean fallbackValue) {
+            return boolValue != null ? boolValue : fallbackValue;
+        }
+
+        public String getStringValue(String fallbackValue) {
+            return strValue != null ? strValue : fallbackValue;
+        }
+    }
+
+    // Known taglets, standard or ICU extensions
+    static enum TagKind {
+        UNKNOWN("<unknown>"),
+        INTERNAL("internal"),
+        DRAFT("draft"),
+        STABLE("stable"),
+        SINCE("since"),
+        DEPRECATED("deprecated"),
+        AUTHOR("author"),
+        SEE("see"),
+        VERSION("version"),
+        PARAM("param"),
+        RETURN("return"),
+        THROWS("throws"),
+        OBSOLETE("obsolete"),
+        EXCEPTION("exception"),
+        SERIAL("serial"),
+        PROVISIONAL("provisional"), // never used
+        DISCOURAGED("discouraged"), // DecimalFormatSymbols(x13), IslamicCalendar(x2)
+        CATEGORY("category"); // only used in DecimalFormat(x82)
+
+        private final String value;
+
+        private TagKind(String value) {
+            this.value = value;
+        }
+
+        static TagKind ofTag(BlockTagTree tag) {
+            for (TagKind tk : TagKind.values()) {
+                if (tk.value.equals(tag.getTagName())) {
+                    return tk;
+                }
+            }
+            return TagKind.UNKNOWN;
+        }
+    }
+
+    // Known ICU taglets
+    static enum IcuTagKind {
+        UNKNOWN("<unknown>"),
+        ICU("icu"),
+        ICUNOTE("icunote"),
+        ICUENHANCED("icuenhanced");
+
+        private final String value;
+
+        private IcuTagKind(String value) {
+            this.value = value;
+        }
+
+        static IcuTagKind ofTag(InlineTagTree tag) {
+            for (IcuTagKind tk : IcuTagKind.values()) {
+                if (tk.value.equals(tag.getTagName())) {
+                    return tk;
+                }
+            }
+            return IcuTagKind.UNKNOWN;
+        }
+    }
+}