HADOOP-19932. Prune obsolete classes in org.apache.hadoop.io.serializer (#8585)

[steveloughran]

This cuts out obsolete classes from org.apache.hadoop.io.serializer

• JavaComparator
• JavaSerialization
• DeserializerComparator

These were all tagged as experimental or limited private(hdfs/mapreduce), or Unstable.

Claude was used to do the junit5 to 4 move/conflict resolution.

it actually helped with the initial move, but here code was removed, rather than
added, so the pr didn't contain, rather "the replicant helped with the cleanup".
So did the IDE, FWIW.

AI Tooling

If an AI tool was used:

• The PR includes the phrase "Contains content generated by "
  where is the name of the AI tool used.
• My use of AI contributions follows the ASF legal policy
  https://www.apache.org/legal/generative-tooling.html

[steveloughran]

builds and tests locally; will merge if happy.

[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	13m 33s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 1s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+0 🆗	detsecrets	0m 0s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 9 new or modified test files.
			_ branch-3.4 Compile Tests _
+0 🆗	mvndep	9m 33s		Maven dependency ordering for branch
+1 💚	mvninstall	40m 6s		branch-3.4 passed
+1 💚	compile	16m 43s		branch-3.4 passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 💚	compile	15m 26s		branch-3.4 passed with JDK Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
+1 💚	checkstyle	4m 14s		branch-3.4 passed
+1 💚	mvnsite	2m 34s		branch-3.4 passed
+1 💚	javadoc	2m 9s		branch-3.4 passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 💚	javadoc	2m 39s		branch-3.4 passed with JDK Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
+1 💚	spotbugs	3m 41s		branch-3.4 passed
+1 💚	shadedclient	34m 32s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+0 🆗	mvndep	0m 33s		Maven dependency ordering for patch
+1 💚	mvninstall	1m 27s		the patch passed
+1 💚	compile	16m 5s		the patch passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 💚	javac	16m 5s		the patch passed
+1 💚	compile	15m 28s		the patch passed with JDK Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
+1 💚	javac	15m 28s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	4m 14s		root: The patch generated 0 new + 138 unchanged - 73 fixed = 138 total (was 211)
+1 💚	mvnsite	2m 32s		the patch passed
+1 💚	javadoc	2m 4s		the patch passed with JDK Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04
+1 💚	javadoc	2m 42s		the patch passed with JDK Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
+1 💚	spotbugs	3m 42s		the patch passed
+1 💚	shadedclient	35m 50s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	19m 17s		hadoop-common in the patch passed.
+1 💚	unit	110m 40s		hadoop-mapreduce-client-jobclient in the patch passed.
+1 💚	asflicense	1m 13s		The patch does not generate ASF License warnings.
		366m 32s

Subsystem	Report/Notes
Docker	ClientAPI=1.55 ServerAPI=1.55 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8642/1/artifact/out/Dockerfile
GITHUB PR	#8642
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux 23c0ccabc116 5.15.0-181-generic #191-Ubuntu SMP Fri May 22 19:09:02 UTC 2026 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	branch-3.4 / 3b0d21b
Default Java	Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.27+6-post-Ubuntu-0ubuntu120.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_452-8u452-gaus1-0ubuntu120.04-b09
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8642/1/testReport/
Max. process+thread count	1251 (vs. ulimit of 5500)
modules	C: hadoop-common-project/hadoop-common hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient U: .
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8642/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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