[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 of this PR is to complement the current oneOf jackson polymorphism - to make it possible to supply default fallback value. this is useful e.g. when one wants to specify a default for deduction based polymorphism (FasterXML/jackson-databind#3055) or when one wants to fallback to some no-op class.

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Summary by cubic

Adds Jackson default deserialization fallback for polymorphic oneOf models across all Java generators, kotlin-spring, and the kotlin client. Configure @JsonTypeInfo(defaultImpl = ...) via x-jackson-default-impl or the typeInfoDefaultImpls option.

New Features
- Added typeInfoDefaultImpls: {SchemaName: ClassName}; overrides x-jackson-default-impl per schema.
- Centralized in AbstractJavaCodegen; Java and Spring emit defaultImpl for both Id.NAME and Id.DEDUCTION. kotlin-spring does both; kotlin client supports discriminator-based (Id.NAME) with Jackson.
- Names resolve via toModelName, honoring mappings and DTO prefix/suffix; warns on overrides and unknown targets.
- New vendor extension x-jackson-default-impl; docs updated for java, spring, kotlin-spring, kotlin, and java-camel. java-microprofile disables this (its models don’t use oneOf interfaces).
- Tests added for Java client, Spring, kotlin-spring, and kotlin client covering deduction/discriminator paths, overrides, suffix handling, and absence cases.

^{Written for commit e005ea4. 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.

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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

1 issue found across 17 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/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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cubic-dev-ai · 2026-06-17T22:11:32Z

  allowSetters = true // allows the {{{discriminator.propertyBaseName}}} to be set during deserialization
 )
-@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true)
+@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true{{#vendorExtensions.x-jackson-resolved-default-impl}}, defaultImpl = {{vendorExtensions.x-jackson-resolved-default-impl}}::class{{/vendorExtensions.x-jackson-resolved-default-impl}})


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.

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/kotlin-spring/typeInfoAnnotation.mustache, line 6: <comment>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.</comment> <file context> @@ -3,7 +3,7 @@ allowSetters = true // allows the {{{discriminator.propertyBaseName}}} to be set during deserialization ) -@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true) +@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true{{#vendorExtensions.x-jackson-resolved-default-impl}}, defaultImpl = {{vendorExtensions.x-jackson-resolved-default-impl}}::class{{/vendorExtensions.x-jackson-resolved-default-impl}}) @JsonSubTypes( {{#discriminator.mappedModels}} </file context>

I think this is not a valid issue - defaultImpl does not need to be a @JsonSubTypes subtype.

Jackson's @JsonTypeInfo(defaultImpl = ...) intentionally accepts any class assignable to the field's declared type at the injection site, not just registered subtypes. So one can use e.g. a no-op catch-all class (e.g. class UnknownAnimal : Animal) to absorb unrecognized payloads.

The PR already handles the "unknown model" case correctly by emitting a LOGGER.warn(...) rather than failing.

I want to warn on potential typos, but to not block intentional use of external/no-op fallback classes.

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 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

cubic-dev-ai Bot reviewed Jun 17, 2026

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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

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