[JAVA, JAVA-SPRING, KOTLIN-CLIENT, KOTLIN-SPRING] - feature - add x-jackson-default-impl / typeInfoDefaultImpls support to allow specifying of fallback schema when deserializing by Picazsoo · Pull Request #23955 · OpenAPITools/openapi-generator

Picazsoo · 2026-06-05T13:29:31Z

Purpose

Complements the current oneOf Jackson polymorphism by making it possible to supply a default fallback value for deserialization. This is useful e.g. when you want to specify a default for deduction-based polymorphism (FasterXML/jackson-databind#3055), or when you want to fall back to some no-op class.

This feature is fully opt-in and has no effect on existing usage. Generated output is unchanged unless you explicitly set x-jackson-default-impl or typeInfoDefaultImpls.

What it adds

Emits @JsonTypeInfo(defaultImpl = ...) on polymorphic oneOf interfaces. Two opt-in ways to configure it (both default to disabled):

Vendor extension x-jackson-default-impl: <ClassName> on a schema.
Generator option typeInfoDefaultImpls: {SchemaName: ClassName}, which overrides the vendor extension when both are set for the same schema.

Class names are resolved via toModelName (honoring model mappings and DTO prefix/suffix); warns on overrides and unknown targets.

Scope

Generator	Support
`java` (client)	deduction + discriminator
`spring`	deduction + discriminator
`kotlin-spring`	deduction + discriminator
`kotlin` (client)	discriminator only
`java-microprofile`	disabled (template doesn't route through oneOf interface)

Resolution is centralized in AbstractJavaCodegen (shared by Java + Spring). Templates only emit defaultImpl when a value is resolved, so output is byte-for-byte identical to before for anyone who doesn't opt in.

Tests & docs

Tests added for Java client, Spring, kotlin-spring, and kotlin client, covering deduction/discriminator cases, config override, model-name suffix handling, and a noDefaultImplWhenNeitherSourceIsSet case that confirms no change when unconfigured.
New shared test spec 3_0/spring/jackson-default-impl.yaml.
Docs updated for java, spring, kotlin-spring, kotlin, and java-camel; new x-jackson-default-impl vendor extension registered.

PR checklist

Read the contribution guidelines.
Run the following to build the project and update samples:
```
./mvnw clean package || exit
./bin/generate-samples.sh ./bin/configs/*.yaml || exit
./bin/utils/export_docs_generators.sh || exit
```
(For Windows users, please run the script in WSL)
Commit all changed files.
This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
These must match the expectations made by your contribution.
You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request. - tagging kotlin, java, java-spring committee members: @bbdouglas, @sreeshas, @jfiala, @lukoyanov, @cbornet, @jeff9finger, @karismann, @Zomzog, @lwlee2608, @martin-mfg, @cachescrubber, @welshm, @MelleD, @atextor, @manedev79, @javisst, @borsch, @banlevente, @andrewemery, @4brunu, @yutaka0m, @stefankoppier, @e5l, @dennisameling

Summary by cubic

Adds an opt‑in Jackson default fallback for deserializing oneOf interfaces. Previously no default existed; now, when configured via x-jackson-default-impl or typeInfoDefaultImpls, generators emit @JsonTypeInfo(defaultImpl=...). Unconfigured outputs are unchanged.

Resolves defaults via shared JacksonDefaultImplResolver, preserving FQCNs (add import, emit simple name), honoring schema/import mappings and DTO prefix/suffix; typeInfoDefaultImpls overrides the vendor extension and warns on shadowed or unknown targets; logs use Locale.ROOT.
Emission:
- java and spring: defaultImpl for deduction (Id.DEDUCTION) and discriminator (Id.NAME) oneOf interfaces.
- kotlin-spring: deduction and discriminator; kotlin client: discriminator only.
- java-microprofile: disabled; strips x-jackson-default-impl during model processing.
Template updates: keep @JsonTypeInfo for non‑discriminator oneOf when not using deduction; add defaultImpl to deduction annotations; avoid duplicate @JsonTypeInfo and render on its own line.
Build/docs/samples: move Gradle ext {} before the Android branch across Java templates; fix webclient useJspecify=true; document typeInfoDefaultImpls and the vendor extension; regenerate samples and CI workflows for Java RestClient, Spring Boot, kotlin-spring, kotlin client, and Java Camel; java-camel POJOs can render @JsonInclude/@JsonSetter(nulls=...) when configured.
Adds CodegenConstants.TYPE_INFO_DEFAULT_IMPLS; tests cover deduction/discriminator cases and config precedence across java, spring, kotlin-spring, and kotlin client.

Migration

To enable a default fallback, set x-jackson-default-impl: ClassName on a schema or configure typeInfoDefaultImpls: {SchemaName: ClassName}; the config option overrides the extension. No action required if you do not opt in.

^{Written for commit a007a4c. Summary will update on new commits.}

…foDefaultImpls support Emit `@JsonTypeInfo(defaultImpl = ...)` for both deduction-based and discriminator-based oneOf interfaces. Two configuration sources (config option takes precedence): - Schema extension: `x-jackson-default-impl: ClassName` - Config option: `typeInfoDefaultImpls: {SchemaName: ClassName}` The resolved class name passes through `toModelName()` so schemaMapping, importMapping, and DTO prefix/suffix are all honoured. A LOGGER.warn is emitted when the config option shadows a schema-level annotation.

cubic-dev-ai

1 issue found across 9 files

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jpfinne · 2026-06-05T14:49:22Z

    public static final String USE_SEALED_RESPONSE_INTERFACES = "useSealedResponseInterfaces";
    public static final String COMPANION_OBJECT = "companionObject";
    public static final String SUSPEND_FUNCTIONS = "suspendFunctions";
+    public static final String TYPE_INFO_DEFAULT_IMPLS = "typeInfoDefaultImpls";


Move to CodegenConstants ?

@Picazsoo Could you also add the feature to the java generators?
See src/main/resources/Java/deductionAnnotation.mustache and the different typeInfoAnnotation.mustache under java/libraries

I will take a look at it. And this is early implementation without any polish. I marked temporarily as "ready for review" just to gather early feedback from Cubic

But thanks for the review! I will properly tag you once I think it is ready for wasting human review time (-:

Hi @jpfinne, I added it to the java generators as well.

This is now ready for review

# Conflicts: # modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/spring/KotlinSpringServerCodegenTest.java

…Java generators - Add TYPE_INFO_DEFAULT_IMPLS/DESC constants to CodegenConstants (addresses reviewer request to avoid duplication across SpringCodegen and KotlinSpringServerCodegen) - Move typeInfoDefaultImpls field, option registration, processOpts parsing, and x-jackson-resolved-default-impl resolution loop from SpringCodegen into AbstractJavaCodegen so all Java generators inherit the feature - Remove duplicated code from SpringCodegen; update KotlinSpringServerCodegen to reference CodegenConstants.TYPE_INFO_DEFAULT_IMPLS and apply the same safe instanceof cast fix already present in SpringCodegen - Update Java/deductionAnnotation.mustache: emit defaultImpl = X.class on @JsonTypeInfo(use = DEDUCTION) when x-jackson-resolved-default-impl is set - Update Java/typeInfoAnnotation.mustache: emit defaultImpl = X.class on both @JsonTypeInfo(use = NAME) variants (discriminator present/absent) via discriminator.vendorExtensions.x-jackson-resolved-default-impl - Add JavaClientCodegenTest tests covering deduction, discriminator, typeInfoDefaultImpls config option, and absence cases for Java client Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

cubic-dev-ai

All reported issues were addressed across 17 files

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cubic-dev-ai

9 issues found across 27 files (changes from recent commits).

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/kotlin-spring/typeInfoAnnotation.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/kotlin-spring/typeInfoAnnotation.mustache:6">
P1: Missing validation that the resolved defaultImpl is a subtype of the polymorphic base; misconfigured `x-jackson-default-impl` or `typeInfoDefaultImpls` values will compile but fail at runtime during deserialization.</violation>
</file>

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# Conflicts: # modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java

Picazsoo · 2026-07-01T12:49:27Z

Tagging @wing328 - please consider if this contribution makes sense and if it would make sense for 7.24.0

# Conflicts: # docs/generators/kotlin-spring.md # docs/generators/kotlin.md # modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaClientCodegenTest.java # modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java

cubic-dev-ai

All reported issues were addressed across 333 files

_{Note: This PR contains a large number of files. cubic only reviews up to 200 files per PR, so some files may not have been reviewed. cubic prioritizes the most important files to review.

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cubic-dev-ai

All reported issues were addressed across 74 files (changes from recent commits).

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Picazsoo · 2026-08-08T07:07:36Z

Hi @wing328 , I wonder if this feature is acceptable or not as is?

…on-default # Conflicts: # docs/generators/java-camel.md # docs/generators/spring.md # modules/openapi-generator/src/main/java/org/openapitools/codegen/VendorExtension.java # modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/SpringCodegen.java

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

cubic-dev-ai

All reported issues were addressed across 30 files (changes from recent commits).

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cubic-dev-ai

All reported issues were addressed across 329 files

_{Requires human review: Auto-approval blocked by 2 unresolved issues from a previous review of this commit.

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- Extract shared JacksonDefaultImplResolver used by AbstractJavaCodegen, KotlinClientCodegen and KotlinSpringServerCodegen (dedup resolution logic) - Preserve external/FQN class names for defaultImpl (add import, emit simple name) instead of mangling them through toModelName - JavaMicroprofileServerCodegen: strip x-jackson-default-impl before model post-processing so the vendor extension no longer leaks defaultImpl - Guard typeInfoAnnotation with discriminator in Java/oneof_interface.mustache so deduction-based oneOf keeps defaultImpl and drops the bogus property="" - Correct kotlin-client typeInfoDefaultImpls description (discriminator/jackson only) and regenerate docs/generators/kotlin.md - Move ext{} version block before the android branch in Java build.gradle templates (base + 12 libraries) to fix -Ptarget=android config failure - Default stricter generateJsonInclude/JsonSetterNulls options on Spring-family jackson-default-impl configs and render them in java-camel-server pojo - Add useDeductionForOneOfInterfaces to the restclient sample config - Regenerate all affected samples Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

cubic-dev-ai

All reported issues were addressed across 134 files (changes from recent commits).

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@JsonIgnoreProperties

…ering - oneof_interface.mustache: render typeInfoAnnotation for non-discriminator oneOf when not using deduction, so sealed oneOf interfaces keep their @JsonTypeInfo/@JsonIgnoreProperties (byte-for-byte stable with master); only suppress it in the deduction path to avoid a duplicate @JsonTypeInfo - deductionAnnotation.mustache: add a leading newline and render at column 0 (mirroring typeInfoAnnotation) so @JsonTypeInfo no longer lands on the same line as @generated - webclient build.gradle.mustache: move the stray jspecify implementation out of the ext{} block into dependencies{} so it runs after the java plugin creates the implementation configuration (fixes useJspecify=true builds while keeping ext{} before the android branch) - Regenerate affected Java client samples Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…on-default # Conflicts: # modules/openapi-generator/src/main/resources/Java/libraries/apache-httpclient/build.gradle.mustache # samples/client/echo_api/java/apache-httpclient/build.gradle # samples/client/petstore/java/apache-httpclient-jackson3/build.gradle # samples/client/petstore/java/apache-httpclient/build.gradle

The forbiddenapis check rejects locale-dependent String.format(String, Object...). Pass Locale.ROOT explicitly, matching the convention used across the codegen language classes. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…ver" This reverts commit 9cfd134.

…lver" This reverts commit 57f56be.

Picazsoo · 2026-08-19T21:01:02Z

Hello @wing328, I made the PR up-to-date and resolved all the standing issues.

wing328 · 2026-09-20T15:36:50Z

Just merged it. Sorry for the delay as I missed it.

Picazsoo · 2026-09-20T15:38:09Z

No problem, thanks a bunch!

Picazsoo marked this pull request as ready for review June 5, 2026 13:29

Picazsoo marked this pull request as draft June 5, 2026 13:29

cubic-dev-ai Bot reviewed Jun 5, 2026

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Comment thread modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/SpringCodegen.java Outdated

jpfinne reviewed Jun 5, 2026

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Picazsoo and others added 4 commits June 17, 2026 23:18

Merge branch 'master' into feature/use-deduction-default

ffc95a7

# Conflicts: # modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/spring/KotlinSpringServerCodegenTest.java

implement CR feedback suggestion

d88082a

update documentation

de72ad2

Picazsoo changed the title ~~feat(kotlin-spring, java-spring): add x-jackson-default-impl / typeInfoDefaultImpls support~~ [kotlin-spring, java(-spring)] -feature - add x-jackson-default-impl / typeInfoDefaultImpls support to allow specifying of fallback schema when deserializing Jun 17, 2026

Picazsoo marked this pull request as ready for review June 17, 2026 22:07

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Comment thread modules/openapi-generator/src/main/resources/kotlin-spring/typeInfoAnnotation.mustache

Picazsoo added 3 commits June 18, 2026 00:18

document the new vendor extension

98ddfb9

feat: add warning for unresolved models in vendor extensions

41dcc13

update documentation

57535bf

cubic-dev-ai Bot reviewed Jun 18, 2026

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Picazsoo added 4 commits June 18, 2026 10:15

address CR feedback and update documentation

7f2856b

address CR feedback and update documentation

378ac1e

address CR feedback and update documentation

3e19fd9

add to kotlin-client as well.

ea94f96

Merge branch 'master' into feature/use-deduction-default

e005ea4

# Conflicts: # modules/openapi-generator/src/test/java/org/openapitools/codegen/java/spring/SpringCodegenTest.java

Picazsoo requested a review from jpfinne July 1, 2026 12:48

Picazsoo added 2 commits July 13, 2026 00:12

add compiled samples

a5e2a3d

cubic-dev-ai Bot reviewed Jul 15, 2026

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fix compiled samples

9fa7541

Picazsoo added 3 commits July 15, 2026 23:48

implement CR feedback

b168935

Merge branch 'master' into feature/use-deduction-default

637abce

updated samples

9ae62a1

cubic-dev-ai Bot reviewed Aug 7, 2026

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Comment thread ...rs/java/restclient-jackson-default-impl/src/main/java/org/openapitools/client/ApiClient.java

Comment thread samples/client/others/java/restclient-jackson-default-impl/.openapi-generator/FILES

updated samples

fb5132e

Picazsoo and others added 2 commits August 13, 2026 20:21

Update samples and documentation

8d5365a

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Comment thread ...tore/kotlin-spring-oneof-jackson-default-impl/src/main/kotlin/org/openapitools/model/Soda.kt

Comment thread ...store/spring-boot-oneof-jackson-default-impl/src/main/java/org/openapitools/model/Apple.java

cubic-dev-ai Bot reviewed Aug 18, 2026

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cubic-dev-ai Bot reviewed Aug 19, 2026

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Picazsoo and others added 6 commits August 19, 2026 20:35

Revert "Use Locale.ROOT with String.format in JacksonDefaultImplResol…

57f56be

…ver" This reverts commit 9cfd134.

Reapply "Use Locale.ROOT with String.format in JacksonDefaultImplReso…

2fd5dd9

…lver" This reverts commit 57f56be.

updated samples

a007a4c

wing328 merged commit cc2e80d into OpenAPITools:master Sep 20, 2026
324 checks passed

wing328 added this to the 7.26.0 milestone Oct 6, 2026

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Purpose

What it adds

Scope

Tests & docs

PR checklist

Summary by cubic

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