[Java] [Spring] 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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java | @bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04) @lwlee2608 (2019/10) @martin-mfg (2023/08)
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Summary by cubic

Adds optional support for inline oneOf combined with properties/allOf (no discriminator) in Java and Spring generators by moving oneOf into a @JsonUnwrapped field. When oneOf interfaces are enabled, a wrapper interface with a @JsonCreator and Jackson mixins ensures correct (de)serialization. Fixes #23759.

New Features
- New option useWrapperForMixedOneOf (default false) in java, java-microprofile, spring, and java-camel.
- When enabled (and no discriminator): inline oneOf is moved to <SchemaName>OneOfWrapper and exposed as a oneOf field annotated with @JsonUnwrapped.
- Works with or without useOneOfInterfaces:
  - With interfaces: the wrapper is an interface; adds @JsonCreator valueOf(JsonNode) and an inner mixin using @JsonTypeInfo(Id.DEDUCTION)/@JsonSubTypes; generates JacksonMixinConfig to register mixins.
  - Without interfaces: the wrapper is a class; no mixins or @JsonCreator.
- Supports Jackson 2 and 3; updates import mappings for JsonNode, JsonMapper, and JsonUnwrapped; hooks mixins via JsonMapper (Jackson 3) or ObjectMapper (Jackson 2).
- Updates templates and tests for Java client and Spring Boot 3/4; docs list the new option across generators.
Bug Fixes
- Avoids a possible NPE when preprocessing oneOf schemas during interface generation.

^{Written for commit fd72fd3. 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 · 2026-05-11T18:26:10Z

+                .add(cm.classname);
+
+        cm.getVendorExtensions().put("x-oneof-jsonCreator", true);
+        obj.getImports().add(Map.of("import", importMapping.get("JsonNode")));


P1: Unconditionally wrapping importMapping.get("JsonNode") in Map.of(...) can NPE when that mapping is absent.

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/languages/AbstractJavaCodegen.java, line 2872: <comment>Unconditionally wrapping `importMapping.get("JsonNode")` in `Map.of(...)` can NPE when that mapping is absent.</comment> <file context> @@ -2809,4 +2814,61 @@ protected void addNullableImportForOperation(CodegenOperation codegenOperation) + .add(cm.classname); + + cm.getVendorExtensions().put("x-oneof-jsonCreator", true); + obj.getImports().add(Map.of("import", importMapping.get("JsonNode"))); + } } </file context>

Suggested change

obj.getImports().add(Map.of("import", importMapping.get("JsonNode")));

String jsonNodeImport = importMapping.get("JsonNode");

if (jsonNodeImport != null) {

obj.getImports().add(Map.of("import", jsonNodeImport));

}

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.}

cubic-dev-ai · 2026-05-11T22:25:21Z

+            newOneOfSchema.addExtension("x-unwrappedOneOf", true);
+            String nOneOf = toModelName(schemaName + "OneOf");
+            String newSchemaName = nOneOf+ "_wrapper";
+            openAPI.getComponents().getSchemas().put(newSchemaName, newOneOfSchema);


P1: Wrapper schema names are deterministic and inserted without any collision check, so this can overwrite an existing component schema.

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/languages/AbstractJavaCodegen.java, line 2830: <comment>Wrapper schema names are deterministic and inserted without any collision check, so this can overwrite an existing component schema.</comment> <file context> @@ -2809,4 +2814,61 @@ protected void addNullableImportForOperation(CodegenOperation codegenOperation) + newOneOfSchema.addExtension("x-unwrappedOneOf", true); + String nOneOf = toModelName(schemaName + "OneOf"); + String newSchemaName = nOneOf+ "_wrapper"; + openAPI.getComponents().getSchemas().put(newSchemaName, newOneOfSchema); + Schema newSchemaRef = new Schema().$ref("#/components/schemas/" + newSchemaName); + s.oneOf(null); </file context>

cubic-dev-ai · 2026-05-11T22:25:21Z

+                oneOf.oneOf(composed.getOneOf());
+                composed.oneOf(null);
+
+                String oneOfName = (String)vendorExtensions.get("x-one-of-name");


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.

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/DefaultCodegen.java, line 2751: <comment>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.</comment> <file context> @@ -2710,13 +2738,23 @@ protected void updateModelForComposedSchema(CodegenModel m, Schema schema, Map<S + oneOf.oneOf(composed.getOneOf()); + composed.oneOf(null); + + String oneOfName = (String)vendorExtensions.get("x-one-of-name"); + oneOfName = oneOfName != null ? "oneOf"+ oneOfName: "oneOf"; + addVars(m, Map.of(oneOfName, oneOf), List.of(), null, null); </file context>

Suggested change

String oneOfName = (String)vendorExtensions.get("x-one-of-name");

String oneOfName = composed.getExtensions() != null ? (String) composed.getExtensions().get(X_ONE_OF_NAME) : null;

cubic-dev-ai · 2026-05-11T22:25:21Z

+                .add(cm.classname);
+
+        cm.getVendorExtensions().put("x-oneof-jsonCreator", true);
+        obj.getImports().add(Map.of("import", importMapping.get("JsonNode")));


P2: Unconditional Map.of call can throw if JsonNode is not mapped for this generator.

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/languages/AbstractJavaCodegen.java, line 2872: <comment>Unconditional `Map.of` call can throw if `JsonNode` is not mapped for this generator.</comment> <file context> @@ -2809,4 +2814,61 @@ protected void addNullableImportForOperation(CodegenOperation codegenOperation) + .add(cm.classname); + + cm.getVendorExtensions().put("x-oneof-jsonCreator", true); + obj.getImports().add(Map.of("import", importMapping.get("JsonNode"))); + } } </file context>

Suggested change

obj.getImports().add(Map.of("import", importMapping.get("JsonNode")));

obj.getImports().add(Map.of("import", importMapping.getOrDefault("JsonNode", "com.fasterxml.jackson.databind.JsonNode")));

cubic-dev-ai · 2026-05-11T22:25:21Z

+            // TODO: configuration of the property name
+            String propertyName = "oneOf";
+            if (ModelUtils.hasProperties(s)) {
+                s.getProperties().put(propertyName, newSchemaRef);


P2: Hardcoded synthetic property name "oneOf" can silently overwrite an existing schema property with the same name

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/languages/AbstractJavaCodegen.java, line 2836: <comment>Hardcoded synthetic property name "oneOf" can silently overwrite an existing schema property with the same name</comment> <file context> @@ -2809,4 +2814,61 @@ protected void addNullableImportForOperation(CodegenOperation codegenOperation) + // TODO: configuration of the property name + String propertyName = "oneOf"; + if (ModelUtils.hasProperties(s)) { + s.getProperties().put(propertyName, newSchemaRef); + } else if (ModelUtils.hasAllOf(s)) { + Schema schema = new Schema(); </file context>

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?

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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Mattias-Sehlstedt reviewed May 12, 2026

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[Java] [Spring] mixed OneOf support and jackson JsonUnwrapped#23761

[Java] [Spring] mixed OneOf support and jackson JsonUnwrapped#23761
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edited by cubic-dev-ai Bot

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-        obj.getImports().add(Map.of("import", importMapping.get("JsonNode")));
+        String jsonNodeImport = importMapping.get("JsonNode");
+        if (jsonNodeImport != null) {
+            obj.getImports().add(Map.of("import", jsonNodeImport));
+        }

	String oneOfName = (String)vendorExtensions.get("x-one-of-name");
	String oneOfName = composed.getExtensions() != null ? (String) composed.getExtensions().get(X_ONE_OF_NAME) : null;

	obj.getImports().add(Map.of("import", importMapping.get("JsonNode")));
	obj.getImports().add(Map.of("import", importMapping.getOrDefault("JsonNode", "com.fasterxml.jackson.databind.JsonNode")));

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jpfinne commented May 11, 2026 •

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