Apply Java convention from remaining projects

[bric3]

What Does This Do

Apply dd-trace-java.conventions.java from the remaining projects that directly applied gradle/java.gradle.

Make the Java and Shadow plugins explicit in the benchmark integration child projects, and update the Spotless guard so direct Java script applications are forbidden everywhere.

Motivation

Continue the incremental APMLP-610 script-plugin migration through project-facing convention plugins.

See #12258.

Additional Notes

The Java convention still delegates to gradle/java.gradle; moving that implementation into build logic remains separate follow-up work. dd-java-agent retains a publish-only Spotless exception because migrating gradle/publish.gradle is outside this change.

Contributor Checklist

• Format the title according to the contribution guidelines
• Assign the type: and (comp: or inst:) labels in addition to any other useful labels
• Avoid using close, fix, or any linking keywords when referencing an issue
  Use solves instead, and assign the PR milestone to the issue
• Update the CODEOWNERS file on source file addition, migration, or deletion
• Update public documentation with any new configuration flags or behaviors
• Once approved, use merge queue to merge the PR

[datadog-prod-us1-5]

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 58.78% (-0.00%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 65c0c56 | Docs | View more details | Give us feedback!}

[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	14.87 s	14.86 s	[-0.9%; +1.0%] (no difference)
startup:insecure-bank:tracing:Agent	13.58 s	13.83 s	[-2.5%; -1.0%] (significantly better)
startup:petclinic:appsec:Agent	17.55 s	17.36 s	[+0.3%; +1.9%] (maybe worse)
startup:petclinic:iast:Agent	17.60 s	17.61 s	[-0.9%; +0.8%] (no difference)
startup:petclinic:profiling:Agent	17.49 s	17.48 s	[-1.2%; +1.4%] (no difference)
startup:petclinic:sca:Agent	17.41 s	17.28 s	[-0.3%; +1.7%] (no difference)
startup:petclinic:tracing:Agent	16.58 s	16.78 s	[-2.2%; -0.1%] (maybe better)

Commit: 65c0c563 · CI Pipeline · Benchmarking Platform UI

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Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

[bric3]

note: The java convention for this module might be too large, but this follows what's existing today.

In the future, a proper convention should be created dd-trace-java.module.distributable.agent for agent jar, this might help to have multiple kind of agent jar distribution (modularization).

The following aspects appears to be needed

• java-base
• java-compilation (to support Java 6 (Pre Java 8) graceful degradation)
• archives / Shadow behavior
• javadoc
• code-quality
• testing
• publishing and dependency locking

Some other "features" may not be needed.

[datadog-prod-us1-5]

More details

The convention plugins preserve the prior Java, Kotlin, Groovy, test suite, and test fixture setup. The Spotless exception stays limited to the publish script in dd-java-agent.

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