Description of PR

JIRA:HADOOP-19402. [JDK11] JDiff Support JDK11.

This PR restores the ability to generate JDiff API XML on JDK 17 by porting Hadoop’s in‑tree doclets to the modern JDK 9+ Doclet API (jdk.javadoc.doclet), while preserving the legacy command‑line surface and XML output contract used in our release process.

Background. The original JDiff tool and its legacy doclet APIs predate JPMS and JDK 9; the upstream artifact (jdiff:1.0.9) is from 2005 and does not support JDK 9+ doclet APIs. Hadoop’s release process, however, still depends on JDiff XML to publish API diffs between releases.

Why now. Since JEP 221 (JDK 9), the standard com.sun.javadoc doclet path was superseded by jdk.javadoc.doclet.*, and the old doclet was eventually removed/replaced in modern JDKs. To run on JDK 17, we need doclets implemented against the new API.

How was this patch tested?

Built with JDK 17 and the docs profile to ensure JDiff XML is emitted.

mvn -T 1C clean package \
  -Pnative -Pdocs \
  -Drequire.snappy -Drequire.zstd -Drequire.openssl \
  -Djdiff.version=1.1.1-jdk17 \
  -DskipTests -Denforcer.skip=true

This produces JDiff XML for each module. For example, HDFS:
Apache_Hadoop_HDFS_3.5.0-SNAPSHOT.xml

For code changes:

All changes are scoped to the hadoop-annotations module and only affect build-time doclet code.

1. Add a JDK‑specific source set and Maven profile
   • Introduce src/main/java17 under hadoop-common-project/hadoop-annotations.
   • Add a Maven profile jdk17 (activated on JDK ≥ 17) that:
     • Adds the java17 sources via build-helper-maven-plugin.
     • Compiles them with maven-compiler-plugin at -release 17 and -add-modules jdk.javadoc.
   • This keeps JDK 8/11 builds unchanged and makes JDK 17 builds self‑contained.
2. Port / re‑implement the doclets on the new Doclet API (under java17)
   • ExcludePrivateAnnotationsJDiffDoclet
   • IncludePublicAnnotationsJDiffDoclet
   • ExcludePrivateAnnotationsStandardDoclet
   • IncludePublicAnnotationsStandardDoclet
   • The JDiff doclets delegate to the (forked) JDiff implementation and run via Doclet#run(DocletEnvironment).
   • The Standard doclets wrap jdk.javadoc.doclet.StandardDoclet to keep the same inclusion/exclusion semantics when producing regular Javadoc.
3. Port the processing utilities to JDK 17
   • Provide RootDocProcessor and StabilityOptions variants that operate on DocletEnvironment, preserving:
     • audience filtering (exclude @InterfaceAudience.Private / LimitedPrivate)
     • “public‑only” mode (IncludePublic* doclets)
     • stability flags such as unstable, evolving, etc.
4. No changes to runtime or public APIs
   • Everything here runs at doc generation time only.
   • No new third‑party runtime dependencies are introduced.

Related JDiff changes (temporary local test build; JDK 17 adaptation implemented)

I implemented the JDK 17 adaptation in JDiff (port to the jdk.javadoc.doclet API) and validated Hadoop’s docs build using a temporary, locally installed artifact: jdiff:1.1.1-jdk17. This build is not published to Maven Central and is provided only so reviewers can reproduce JDiff XML generation on JDK 17. The implementation is available in zhtttylz/jdiff#4.