[Java] Generate nullability annotations on all-args constructor parameters

[seonwooj0810]

Fixes #24109

Root cause

For the Java client generators, model fields and fluent setters are annotated with the configured nullability annotation (@jakarta/javax.annotation.Nullable / @Nonnull, or JSpecify @Nullable), but the all-args constructor generated by generateConstructorWithAllArgs emitted bare parameter types ({{{datatypeWithEnum}}}). So a nullable optional property appeared as private @javax.annotation.Nullable String baz; with a matching @Nullable setter, yet the all-args constructor parameter baz carried no annotation — an inconsistency for null-safety tooling.

Change

The all-args constructor now reuses the same nullability partial each template already applies to its fluent setter, so the constructor parameters stay consistent with the fields/setters:

• Java/pojo.mustache → {{>nullable_var_annotations}}
• Java/libraries/webclient, restclient, resttemplate pojo.mustache → {{>nullableArgumentWithEnum}}

JavaSpring/pojo.mustache already applied {{>nullableAnnotation}} to its all-args constructor and is left unchanged.

Effect (regenerated samples)

e.g. samples/.../resttemplate/.../Pet.java all-args constructor now matches its setters — required props get @Nonnull, optional props get @Nullable:

public Pet(@JsonProperty(JSON_PROPERTY_ID) @javax.annotation.Nullable Long id,
           @JsonProperty(JSON_PROPERTY_NAME) @javax.annotation.Nonnull String name, ...)

Test / verification

• Extended JavaClientCodegenTest#generateAllArgsConstructor to assert the all-args constructor parameters carry @javax.annotation.Nullable (optional dateOfBirth, name) and @javax.annotation.Nonnull (required type). Fails before the template change, passes after.
• Regenerated the affected samples with the locally built CLI (./bin/generate-samples.sh configs java-resttemplate*); the only sample changes are the added annotations on all-args constructor parameters.

Verification done: built modules/openapi-generator-cli (JDK 21), ran the updated JavaClientCodegenTest all-args tests (2 passed), and confirmed the regenerated sample diff contains exclusively the nullability annotations on all-args constructor parameters.

PR checklist:

• Read the contribution guidelines.
• Ran the associated tests (mvn test -Dtest=JavaClientCodegenTest).
• Filed against master.

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Summary by cubic

Generate nullability annotations on all-args constructor parameters for Java client models to match fields and setters. Fixes #24109 and makes null-safety consistent for tooling.

• Bug Fixes
  • Apply the same nullability partial used by setters to all-args constructor params:
    • Java/pojo.mustache → {{>nullable_var_annotations}}
    • Java/libraries/{webclient,restclient,resttemplate}/pojo.mustache → {{>nullableArgumentWithEnum}}
  • JavaSpring/pojo.mustache already correct; no change.
  • Extend JavaClientCodegenTest#generateAllArgsConstructor to assert @Nullable/@Nonnull on constructor params.
  • Regenerate Java RestTemplate samples (including -jakarta); diffs add only the annotations on constructor parameters.

^{Written for commit d1db710. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 54 files

_{Re-trigger cubic}