FINERACT-2842: Move away from JDK8 in avro and fineract-client

[adamsaghy]

Description

Fixes the run-sonarqube job, failing on develop since the Spring Boot 4.1 upgrade (476b600), and removes the obsolete Java 8 baseline that caused it.

The failure

Could not resolve all files for configuration ':fineract-avro-schemas:testCompileClasspath'.
> Could not resolve org.junit.jupiter:junit-jupiter-api.
  > Dependency resolution is looking for a library compatible with JVM runtime version 8,
    but 'org.junit.jupiter:junit-jupiter-api:6.0.3' is only compatible with JVM runtime version 17 or newer.

The Boot 4 BOM brings JUnit 6.0.3, which requires JVM 17+. fineract-client and fineract-avro-schemas pinned Java 8 via the java {} extension, which applies to every source set — so testCompileClasspath requested a JVM 8 variant and JUnit 6 became unresolvable.

Only Sonar caught it: fineract-avro-schemas has no src/test, so compileTestJava is NO-SOURCE and that configuration is never resolved in a normal build. :sonar resolves every module's test classpath, so it is the only job that trips.

Why drop Java 8 rather than work around it

The pin dates to 0897f17 (Oct 2020), citing FINERACT-1214 — which is actually a bug about the Swagger client returning RxJava Observables. Android appears there only in a wish-list of SDK variants that was never built. Three things make the baseline obsolete:

• For fineract-avro-schemas it was already broken. Avro 1.12.1 is Java 11 bytecode (major 55) and every generated class extends SpecificRecordBase, so a Java 8 JVM would fail with UnsupportedClassVersionError. Gradle never caught this because Avro publishes POM-only metadata, carrying no org.gradle.jvm.version attribute.
• Android no longer needs Java 8 bytecode. Android 14 ships OpenJDK 17 core libraries, and D8 desugars for lower minSdk.
• Nothing is being consumed. No artifacts exist under org.apache.fineract on Maven Central; the only publish anywhere is one ASF snapshot, fineract-client 1.6.1-…-SNAPSHOT, dated May 2022.

Changes

Module	Before	After
fineract-client	Java 8 (major 52)	Java 17 (major 61)
fineract-avro-schemas	Java 8 (major 52)	toolchain, Java 25 (major 69)

fineract-client is set to 17 rather than the toolchain's 25 deliberately: Android 14 provides Java 17 core libraries and AGP still requires/targets JDK 17, so Java 21+ bytecode is not consumable by D8/R8. Letting it inherit the toolchain would emit major 69 and silently break Android consumers. fineract-avro-schemas has no such story — it is consumed only by server-side modules, all on toolchain 25.

Also removed, all tied to that baseline:

• the org.junit:junit-bom:5.14.4 workaround in fineract-client — raising to 17 fixes the incompatibility at its source, so the repo is now uniformly on JUnit 6.0.3
• -Xlint:-options in fineract-avro-schemas, which only silenced javac's "source 8 is obsolete"
• com.squareup.retrofit2:adapter-java8 — unused (the client registers no call adapter factories) and present only because Retrofit's core kept a pre-Java-8 baseline; plus the adapter-java8 / converter-java8 entries in buildSrc
• "fineract-client/**" from renovate.json ignorePaths, added in 971179c as "specific versions for a reason" with the reason never recorded. It blocked exactly two pins: jackson-databind-nullable:0.2.6 (already the latest) and jakarta.annotation-api:1.3.5. The latter is a real constraint but a namespace one, not a Java baseline one — the generated code has 1,464 uses of javax.annotation.Generated, which only exists in the 1.x line. Replaced with a scoped packageRule documenting that, so the module's other dependencies become updatable again.

Left in place deliberately: dateLibrary: 'java8' (in OpenAPI Generator this selects java.time; the alternative is legacy = java.util.Date), jackson-datatype-jdk8, cucumber-java8, jsr305 and jakarta.annotation-api:1.3.5. Despite the names, none are Java 8 compatibility shims.

Verification

• :sonar completes across the whole project (real task, dumpToFile mode, no token needed) — this also confirms no second failure was hiding behind the first.
• :fineract-client:check and :fineract-avro-schemas:check pass with --rerun-tasks, including modernizer, which now evaluates at 17/25 instead of 8.
• :integration-tests:compileTestJava and :fineract-e2e-tests-core:compileTestJava compile — integration-tests is the real consumer of fineract-client, across 473 files.
• Bytecode confirmed with javap; junit-jupiter-api-6.0.3.jar is the only JUnit on any classpath repo-wide.

Note for reviewers

This raises the published baseline for fineract-client from Java 8 to Java 17, so it is a deliberate compatibility change, not just a CI fix. No consumer is believed to be affected given nothing has been published since 2022 — but if you know of a Java 8 consumer of this SDK, please say so here.

Checklist

• Write the commit message as per our guidelines
• Acknowledge that we will not review PRs that are not passing the build ("green")
• Create/update unit or integration tests — N/A: build-configuration change, no production code affected; covered by the existing fineract-client suite and by :sonar itself, the job that regressed.
• Follow our coding conventions.
• Add required Swagger annotation and update API documentation — N/A: no API changes.
• This PR must not be a "code dump" — 5 files, +14/-23.
• If merging this PR resolves a JIRA issue, I will mark that issue as resolved and set "Fix Version/s" appropriately.
• I followed the AI Policy.