[Java][Spring] Use discriminator value for @JsonTypeName instead of schema name (#23997)

[seonwooj0810]

Fixes #23997

Problem

For the java and spring generators, generated child models of a discriminator can receive a Jackson @JsonTypeName annotation using the schema/model name instead of the discriminator value declared in the OpenAPI contract:

@JsonTypeName("ComponentBrLock")               // wrong
public class ComponentBrLockConsumerDTO implements BrLockConsumerDTO { }

This breaks Jackson polymorphic serialization whenever the discriminator value differs from the schema name — most visibly when modelNameSuffix/modelNamePrefix is used, or when an explicit x-discriminator-value is declared on the child schema. The parent's @JsonSubTypes already uses the correct value, so serialization and deserialization disagree.

Fix

Render @JsonTypeName from vendorExtensions.x-discriminator-value when present, falling back to the schema/model name otherwise — exactly the approach suggested in the issue and already used for the jaxrs-spec generator (#23509):

@JsonTypeName("{{#vendorExtensions.x-discriminator-value}}{{{vendorExtensions.x-discriminator-value}}}{{/vendorExtensions.x-discriminator-value}}{{^vendorExtensions.x-discriminator-value}}{{name}}{{/vendorExtensions.x-discriminator-value}}")

Applied to the base Java/JavaSpring pojo.mustache and the affected Java client libraries (restclient, resttemplate, webclient, feign, jersey2, jersey3, microprofile) so the behavior is consistent across the Java/Spring generators.

The change is a no-op when no x-discriminator-value is present (the conditional renders exactly {{name}} as before), so no existing samples change.

Test evidence

Added two focused tests reproducing the issue's spec (child schemas extend a non-discriminator base and carry an explicit x-discriminator-value, generated with a model-name suffix):

• SpringCodegenTest#testDiscriminatorValueUsedInJsonTypeName_issue23997
• JavaClientCodegenTest#testDiscriminatorValueUsedInJsonTypeName_issue23997

Both assert child models emit @JsonTypeName("USER") / @JsonTypeName("COMPONENT") rather than the suffixed schema name. Both pass:

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0  -- SpringCodegenTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0  -- JavaClientCodegenTest

Regenerating an existing discriminator-bearing sample (bin/configs/java-restclient.yaml, petstore) produced zero diff, confirming the template change does not affect output when x-discriminator-value is absent.

Verification done

• (1) No in-flight PR for this issue (gh pr list search), no linked PRs/branches on the issue
• (2) No claim comments (issue had 0 comments)
• (3) Code-focused: fix touches .mustache templates + Java tests, not docs
• (4) Confirmed the bug still exists on master (templates emitted @JsonTypeName("{{name}}")); reproduced via the added tests
• (5) Not part of a closed umbrella epic — related JAX-RS fix [Java][jaxrs-spec] Fix JsonTypeName Generation With allOf and oneOf Combination to Match Key Instead of Schema Name #23509 deliberately did not cover java/spring

cc @bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jimschubert (Java technical committee) and @cachescrubber @welshm @MelleD @atextor @manedev79 @javisst @borsch @banlangzhi @sahilgarg17 (Spring technical committee)

---

Summary by cubic

Use the discriminator value for Jackson @JsonTypeName in Java and Spring generators to fix mismatched polymorphic serialization when it differs from the schema name. Falls back to the model name when no x-discriminator-value is set; no behavior change otherwise. Fixes #23997.

• Bug Fixes
  • Render @JsonTypeName from vendorExtensions.x-discriminator-value, otherwise use {{name}}.
  • Applied to Java/JavaSpring pojo.mustache and Java client libs: restclient, resttemplate, webclient, feign, jersey2, jersey3, microprofile.
  • Added focused tests asserting @JsonTypeName("USER" | "COMPONENT") is emitted; existing samples show zero diff.

^{Written for commit 91b6b9c. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 12 files

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="modules/openapi-generator/src/main/resources/Java/libraries/microprofile/pojo.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/Java/libraries/microprofile/pojo.mustache:17">
P2: `x-discriminator-value` is interpolated raw into a Java string literal via triple-brace Mustache, risking uncompilable generated code if the extension contains quotes, backslashes, or newlines.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P2: x-discriminator-value is interpolated raw into a Java string literal via triple-brace Mustache, risking uncompilable generated code if the extension contains quotes, backslashes, or newlines.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At modules/openapi-generator/src/main/resources/Java/libraries/microprofile/pojo.mustache, line 17:

<comment>`x-discriminator-value` is interpolated raw into a Java string literal via triple-brace Mustache, risking uncompilable generated code if the extension contains quotes, backslashes, or newlines.</comment>

<file context>
@@ -14,7 +14,7 @@
 {{#isClassnameSanitized}}
 {{^hasDiscriminatorWithNonEmptyMapping}}
-@JsonTypeName("{{name}}")
+@JsonTypeName("{{#vendorExtensions.x-discriminator-value}}{{{vendorExtensions.x-discriminator-value}}}{{/vendorExtensions.x-discriminator-value}}{{^vendorExtensions.x-discriminator-value}}{{name}}{{/vendorExtensions.x-discriminator-value}}")
 {{/hasDiscriminatorWithNonEmptyMapping}}
 {{/isClassnameSanitized}}
</file context>