[Java] [Spring] OpenAPI normalizer USE_UNWRAPPED_FOR_COMPOSITE_ONEOF for mixed OneOf support and jackson JsonUnwrapped by jpfinne · Pull Request #23761 · OpenAPITools/openapi-generator

jpfinne · 2026-05-11T17:36:40Z

Support models with oneOf without discriminator combined with properties (or allOf)

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Summary by cubic

Adds optional support for inline oneOf mixed with properties/allOf (no discriminator) in Java and Spring by nesting the union under a new oneOf property annotated with @JsonUnwrapped. When oneOf interfaces are enabled, a static @JsonCreator with Jackson mixins handles (de)serialization. Fixes #23759.

New Features
- Enable via OpenAPI normalizer rule USE_UNWRAPPED_FOR_COMPOSITE_ONEOF (sets x-oneOfunwrapped); the original inline oneOf is moved under a new oneOf property which generators annotate with @JsonUnwrapped.
- With useOneOfInterfaces=true: generate a valueOf(JsonNode) @JsonCreator, a nested mixin using @JsonTypeInfo(Id.DEDUCTION)/@JsonSubTypes, and a JacksonMixinConfig that registers mixins and provides a mapper.
- With useOneOfInterfaces=false: generate a normal class (no mixins or @JsonCreator).
- Supports Jackson 2 and 3; adds import mappings for JsonNode and JsonMapper; generates mixin config for both Java client and Spring Boot 3/4.
- Centralizes Jackson and vendor extension constants in CodegenConstants (JACKSON2_PACKAGE, JACKSON3_PACKAGE, jacksonPackage, x-oneOfunwrapped, x-oneof-jsonCreator) to align generators.
Bug Fixes
- Prevent a potential NPE when preprocessing oneOf schemas during interface generation.

^{Written for commit 5ebc7e2. Summary will update on new commits.}

…e/inlineOneOfWithProperties

merge master

cubic-dev-ai

2 issues 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/Java/jacksonMixinConfig.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/Java/jacksonMixinConfig.mustache:19">
P1: Unsynchronized lazy initialization can overwrite a concurrently supplied custom mapper and make mapper configuration nondeterministic.</violation>
</file>

<file name="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java">

<violation number="1" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java:2872">
P1: Unconditionally wrapping `importMapping.get("JsonNode")` in `Map.of(...)` can NPE when that mapping is absent.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

cubic-dev-ai · 2026-05-11T18:26:10Z

@@ -0,0 +1,44 @@
+package {{invokerPackage}};


P1: Unsynchronized lazy initialization can overwrite a concurrently supplied custom mapper and make mapper configuration nondeterministic.

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/jacksonMixinConfig.mustache, line 19: <comment>Unsynchronized lazy initialization can overwrite a concurrently supplied custom mapper and make mapper configuration nondeterministic.</comment> <file context> @@ -0,0 +1,44 @@ + Get the {{vendorExtensions.x-jackson-mixins-mapper}} used by the @JsonCreator in @JsonUnWrapped interfaces. + */ + public static {{vendorExtensions.x-jackson-mixins-mapper}} getMapper() { + if (INSTANCE == null) { + setBuilder({{^useJackson3}}JsonMapper.builder().findAndAddModules(){{/useJackson3}}{{#useJackson3}}JsonMapper.shared().rebuild(){{/useJackson3}}); + } </file context>

cubic-dev-ai

4 issues 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/java/org/openapitools/codegen/DefaultCodegen.java">

<violation number="1" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java:2751">
P2: Reads `x-one-of-name` from the generator-level `vendorExtensions` map instead of the current schema, so the schema-scoped oneOf name added during preprocessing is ignored.</violation>
</file>

<file name="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java">

<violation number="1" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java:2830">
P1: Wrapper schema names are deterministic and inserted without any collision check, so this can overwrite an existing component schema.</violation>

<violation number="2" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java:2836">
P2: Hardcoded synthetic property name "oneOf" can silently overwrite an existing schema property with the same name</violation>

<violation number="3" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java:2872">
P2: Unconditional `Map.of` call can throw if `JsonNode` is not mapped for this generator.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

Mattias-Sehlstedt · 2026-05-12T19:51:02Z

        if (property.dataType != null && property.dataType.equals(property.name) && property.dataType.toUpperCase(Locale.ROOT).equals(property.name)) {
            property.name = property.name.toLowerCase(Locale.ROOT);
        }
+        if (property.getVendorExtensions().containsKey("x-unwrappedOneOf")) {


Could we add this to the vendor extensions that are defined in CodegenConstants to encourage reuse of vendor extensions between language implementations.

Mattias-Sehlstedt · 2026-05-12T19:54:27Z

    }
+
+    @Override
+    protected void preprocessMixedOneOf(Schema s, String schemaName) {


Should this discriminator logic be moved out into a separate component to highlight that it might be of "general interest" between languages rather than strictly tied to Java?

I find that the library is now starting to support a lot of scenarios, and especially that Java spearheads those changes with your contributions. I believe that it would be preferable if the logic for handling these scenarios was generalized directly if possible.

@Mattias-Sehlstedt initially I put the logic as an OpenapiNormalizer. It was in fact simpler than finding the right place in the DefaultCodeGen.

Proposal:

The normalizer implements the logic of AbstractJavaCodeGen.preprocessMixedOneOf with a new rule USE_WRAPPER_FOR_MIXED_ONE_OF

Remove the option from the java generators. The generators detect the constant x-unwrappedOneOf and configure the imports and the correct vendor extensions (also using constants)

moving a few common functionalities from JavaClientCodeGen and SpringCodeGen to AbstractJavaCodeGen (isJackson3(), getConfigOrInvokerPackage()....)

What do you think?

@Mattias-Sehlstedt now an OpenapiNormalizer. The downside is the naming convention (OneOf sufix)

It being handled as a normalized I believe is generally preferred since then the codegen logic can be centralized towards "best practices" regarding how to express concepts with OAS.

For the suffix, is that technically something that would be possible to attached to the naming mappers? (e.g., the inline naming one). I have personally not used them myself since I have always avoided inline models.

# Conflicts: # modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java # modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java # modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaClientCodegenTest.java

cubic-dev-ai

1 issue found across 15 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/java/org/openapitools/codegen/DefaultCodegen.java">

<violation number="1">
P1: NullPointerException risk when components.schemas is null in preprocessOpenAPI</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

jpfinne · 2026-05-14T21:18:44Z

@cubic-dev-ai

cubic-dev-ai · 2026-05-14T21:18:49Z

@cubic-dev-ai

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cubic-dev-ai

3 issues found across 16 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/jacksonMixinConfig.mustache">

<violation number="1" location="modules/openapi-generator/src/main/resources/Java/jacksonMixinConfig.mustache:44">
P1: Class closing brace is outside the conditional Mustache section, producing invalid Java if the section is omitted</violation>
</file>

<file name="modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java">

<violation number="1" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java:1108">
P1: NullPointerException in processUnwrapCompositeOneOf when oneOf list contains null elements. normalizeOneOf explicitly tolerates null entries (`if (item == null) continue;`) but processUnwrapCompositeOneOf's stream allMatch dereferences elements without null checking (`oneOf.get$ref()`), causing an NPE.</violation>

<violation number="2" location="modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java:1125">
P2: Synthetic `oneOf` property can silently overwrite an existing user-defined `oneOf` property</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

cubic-dev-ai · 2026-05-14T21:24:08Z

+          .addMixIn({{.}}.class, {{.}}.{{.}}Mixin.class){{/mixins}}
+          .build();
+    }
+ {{/vendorExtensions.x-jacksonMixinConfig}}


P1: Class closing brace is outside the conditional Mustache section, producing invalid Java if the section is omitted

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/jacksonMixinConfig.mustache, line 44: <comment>Class closing brace is outside the conditional Mustache section, producing invalid Java if the section is omitted</comment> <file context> @@ -0,0 +1,45 @@ + .addMixIn({{.}}.class, {{.}}.{{.}}Mixin.class){{/mixins}} + .build(); + } + {{/vendorExtensions.x-jacksonMixinConfig}} +} \ No newline at end of file </file context>

cubic-dev-ai · 2026-05-14T21:24:08Z

+        boolean hasDiscriminator = schema.getDiscriminator() != null;
+        if (hasDiscriminator) {
+            List<Schema> oneOfs = schema.getOneOf();
+            if (oneOfs.stream().allMatch(oneOf -> oneOf.get$ref() != null)) {


P1: NullPointerException in processUnwrapCompositeOneOf when oneOf list contains null elements. normalizeOneOf explicitly tolerates null entries (if (item == null) continue;) but processUnwrapCompositeOneOf's stream allMatch dereferences elements without null checking (oneOf.get$ref()), causing an NPE.

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/java/org/openapitools/codegen/OpenAPINormalizer.java, line 1108: <comment>NullPointerException in processUnwrapCompositeOneOf when oneOf list contains null elements. normalizeOneOf explicitly tolerates null entries (`if (item == null) continue;`) but processUnwrapCompositeOneOf's stream allMatch dereferences elements without null checking (`oneOf.get$ref()`), causing an NPE.</comment> <file context> @@ -1087,6 +1091,49 @@ protected Schema normalizeOneOf(Schema schema, Set<Schema> visitedSchemas) { + boolean hasDiscriminator = schema.getDiscriminator() != null; + if (hasDiscriminator) { + List<Schema> oneOfs = schema.getOneOf(); + if (oneOfs.stream().allMatch(oneOf -> oneOf.get$ref() != null)) { + // skip normalization if discriminator but not maping + if (discriminator.getMapping() == null && discriminator.getPropertyName() != null) { </file context>

Suggested change

if (oneOfs.stream().allMatch(oneOf -> oneOf.get$ref() != null)) {

if (oneOfs.stream().allMatch(oneOf -> oneOf != null && oneOf.get$ref() != null)) {

cubic-dev-ai · 2026-05-14T21:24:08Z

+        newOneOfSchema.addExtension(X_ONE_OF_UNWRAPPED, true);
+        schema.oneOf(null);
+        // TODO: configuration of the property name
+        String propertyName = "oneOf";


P2: Synthetic oneOf property can silently overwrite an existing user-defined oneOf property

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/java/org/openapitools/codegen/OpenAPINormalizer.java, line 1125: <comment>Synthetic `oneOf` property can silently overwrite an existing user-defined `oneOf` property</comment> <file context> @@ -1087,6 +1091,49 @@ protected Schema normalizeOneOf(Schema schema, Set<Schema> visitedSchemas) { + newOneOfSchema.addExtension(X_ONE_OF_UNWRAPPED, true); + schema.oneOf(null); + // TODO: configuration of the property name + String propertyName = "oneOf"; + if (ModelUtils.hasProperties(schema)) { + schema.getProperties().put(propertyName, newOneOfSchema); </file context>

jpfinne added 8 commits May 7, 2026 21:33

wip

2e9ba37

Merge remote-tracking branch 'refs/remotes/origin/master' into featur…

5a4dd70

…e/inlineOneOfWithProperties

useWrapperForMixedOneOf

a6f9281

useWrapperForMixedOneOf

cd2a1c5

regenerate doc

c132be4

Merge pull request #4 from OpenAPITools/master

59c67f2

merge master

Merge branch 'master' into feature/inlineOneOfWithProperties

a286059

regenerate doc

32eb110

jpfinne marked this pull request as ready for review May 11, 2026 18:21

cubic-dev-ai Bot reviewed May 11, 2026

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jpfinne marked this pull request as draft May 11, 2026 20:00

jpfinne changed the title ~~[Java] [Spring] mixed OneOf support with inheritance and JsonUnwrapped~~ [Java] [Spring] mixed OneOf support and JsonUnwrapped May 11, 2026

Support for useOneOfInterfaces=false

d38d951

jpfinne changed the title ~~[Java] [Spring] mixed OneOf support and JsonUnwrapped~~ [Java] [Spring] mixed OneOf support and jackson JsonUnwrapped May 11, 2026

jpfinne added 4 commits May 11, 2026 23:37

Better backward compatiblity

ceb1af9

Avoid NPE

536d359

Better backward compatiblity

822085e

test for interface/normalClass

fd72fd3

jpfinne marked this pull request as ready for review May 11, 2026 22:14

cubic-dev-ai Bot reviewed May 11, 2026

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Merge branch 'OpenAPITools:master' into master

784da69

Mattias-Sehlstedt reviewed May 12, 2026

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jpfinne added 2 commits May 13, 2026 00:39

Move the cliOption to the OpenAPINormalizer

2f06df2

cubic-dev-ai Bot reviewed May 14, 2026

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jpfinne added 2 commits May 14, 2026 20:06

Normalize mixed content

e04af45

Rename USE_UNWRAPPED_FOR_COMPOSITE_ONEOF

997b859

jpfinne changed the title ~~[Java] [Spring] mixed OneOf support and jackson JsonUnwrapped~~ [Java] [Spring] OpenAPI normalizer USE_UNWRAPPED_FOR_COMPOSITE_ONEOF for mixed OneOf support and jackson JsonUnwrapped May 14, 2026

Rename method to processUnwrapCompositeOneOf

5f0bfe1

Move more constants to CodegenConstants

5ebc7e2

cubic-dev-ai Bot reviewed May 14, 2026

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	if (oneOfs.stream().allMatch(oneOf -> oneOf.get$ref() != null)) {
	if (oneOfs.stream().allMatch(oneOf -> oneOf != null && oneOf.get$ref() != null)) {

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jpfinne commented May 11, 2026 •

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