[Java] [apache-httpclient] Add support for Jackson3 for apache httpclient generator (fixes #22294)

[maksimkurb]

This PR continues work of #23071 and adds Jackson3 support for the apache-httpclient library.
Related issue: #22294

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  (For Windows users, please run the script in WSL)
  Commit all changed files.
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---

Summary by cubic

Adds Jackson 3 support to the Java apache-httpclient generator and enables OpenAPI Nullable with JsonNullableJackson3Module across Jackson 3 clients. Fixes #22294.

• New Features

  • Enable useJackson3=true for apache-httpclient (Java 17); configures JsonMapper, DateTimeFeature, and EnumFeature.
  • Add OpenAPI Nullable for Jackson 3 via JsonNullableJackson3Module in apache-httpclient, native, and Spring resttemplate/webclient/restclient.
  • New sample samples/client/petstore/java/apache-httpclient-jackson3 with Gradle/Maven; CI builds it on JDK 17/21.
  • Tests cover Jackson 3 + OpenAPI Nullable; docs updated to list apache-httpclient support.

• Dependencies

  • Jackson 3 uses tools.jackson (jackson-core, jackson-databind 3.1.0) with com.fasterxml.jackson.core:jackson-annotations 2.21; add org.openapitools:jackson-databind-nullable:0.2.10 when openApiNullable=true.
  • Gradle/Maven templates switch to Java 17 when useJackson3 is set; otherwise remain on Java 8. Gradle tests use JUnit Platform.
  • echo_api apache-httpclient sample updated to JUnit 5.

^{Written for commit cac750d. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 231 files

Note: This PR contains a large number of files. cubic only reviews up to 75 files per PR, so some files may not have been reviewed.

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="samples/client/petstore/java/apache-httpclient-jackson3/docs/FakeApi.md">

<violation number="1" location="samples/client/petstore/java/apache-httpclient-jackson3/docs/FakeApi.md:1007">
P2: Java example uses invalid enum literal `-efg`; should reference the generated enum constant (e.g., `EnumClass._EFG`).</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P2: Java example uses invalid enum literal -efg; should reference the generated enum constant (e.g., EnumClass._EFG).

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/petstore/java/apache-httpclient-jackson3/docs/FakeApi.md, line 1007:

<comment>Java example uses invalid enum literal `-efg`; should reference the generated enum constant (e.g., `EnumClass._EFG`).</comment>

<file context>
@@ -0,0 +1,1541 @@
+        String enumQueryString = "_abc"; // String | Query parameter enum test (string)
+        Integer enumQueryInteger = 1; // Integer | Query parameter enum test (double)
+        Double enumQueryDouble = 1.1D; // Double | Query parameter enum test (double)
+        List<EnumClass> enumQueryModelArray = Arrays.asList(-efg); // List<EnumClass> | 
+        List<String> enumFormStringArray = Arrays.asList("$"); // List<String> | Form parameter enum test (string array)
+        String enumFormString = "_abc"; // String | Form parameter enum test (string)
</file context>

[maksimkurb]

@cubic-dev-ai Please review everything except samples/ directory, as samples/ folder contains too much codegenerated files and you only have a limit of 75 files

[cubic-dev-ai]

@cubic-dev-ai Please review everything except samples/ directory, as samples/ folder contains too much codegenerated files and you only have a limit of 75 files

@maksimkurb I have started the AI code review. It will take a few minutes to complete.

[cubic-dev-ai]

4 issues found across 231 files

Note: This PR contains a large number of files. cubic only reviews up to 75 files per PR, so some files may not have been reviewed.

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name=".github/workflows/samples-java-client-jdk17.yaml">

<violation number="1" location=".github/workflows/samples-java-client-jdk17.yaml:17">
P2: Workflow path/matrix uses `samples/client/others/java/apache-httpclient-jackson3`, but the sample exists under `samples/client/petstore/java/apache-httpclient-jackson3`, so CI will miss changes or fail when running the matrix entry.</violation>
</file>

<file name="samples/client/echo_api/java/apache-httpclient/build.gradle">

<violation number="1" location="samples/client/echo_api/java/apache-httpclient/build.gradle:143">
P2: JUnit 5 test configuration is applied globally, including Android target builds, which can break Android test/build behavior.</violation>
</file>

<file name="samples/client/petstore/java/apache-httpclient-jackson3/build.sbt">

<violation number="1" location="samples/client/petstore/java/apache-httpclient-jackson3/build.sbt:1">
P2: build.sbt contains an invalid `#` comment, which will cause SBT parsing to fail and make the sample non-buildable.</violation>
</file>

<file name="docs/generators/java-microprofile.md">

<violation number="1" location="docs/generators/java-microprofile.md:100">
P2: `useJackson3` is documented as incompatible with `openApiNullable`, but the apache-httpclient templates now support JsonNullable with Jackson 3, so the docs are misleading.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P2: build.sbt contains an invalid # comment, which will cause SBT parsing to fail and make the sample non-buildable.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At samples/client/petstore/java/apache-httpclient-jackson3/build.sbt, line 1:

<comment>build.sbt contains an invalid `#` comment, which will cause SBT parsing to fail and make the sample non-buildable.</comment>

<file context>
@@ -0,0 +1 @@
+# TODO
</file context>

[maksimkurb]

Hi @wing328 , I've received an email that you have approved workflow run and then CI/CD failed. I've pushed a commit with chmod +x on the gradle wrapper and another shell script in generated sample