feat(kotlin-spring, java-spring): add x-jackson-default-impl / typeInfoDefaultImpls support

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java

@@ -110,6 +110,7 @@ public class KotlinSpringServerCodegen extends AbstractKotlinCodegen
     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";
 
     @Getter
     public enum DeclarativeInterfaceReactiveMode {
@@ -186,6 +187,8 @@ public String getDescription() {
     @Getter @Setter
     protected boolean useDeductionForOneOfInterfaces = false;
 
+    private Map<String, String> typeInfoDefaultImpls = new HashMap<>();
+
     @Getter @Setter
     protected boolean useSpringBoot3 = false;
     @Getter @Setter
@@ -311,6 +314,7 @@ public KotlinSpringServerCodegen() {
         addSwitch(COMPANION_OBJECT, "Whether to generate companion objects in data classes, enabling companion extensions.", companionObject);
         addSwitch(SUSPEND_FUNCTIONS, "Whether to generate suspend functions for API operations. Useful for Spring MVC with Kotlin coroutines without requiring the full reactive stack.", suspendFunctions);
         cliOptions.add(CliOption.newBoolean(CodegenConstants.USE_DEDUCTION_FOR_ONE_OF_INTERFACES, CodegenConstants.USE_DEDUCTION_FOR_ONE_OF_INTERFACES_DESC, useDeductionForOneOfInterfaces));
+        addOption(TYPE_INFO_DEFAULT_IMPLS, "Map of schema name to default Jackson deserialization class for @JsonTypeInfo(defaultImpl=...). Applies to both deduction-based and discriminator-based oneOf interfaces. Overrides x-jackson-default-impl when both are set for the same schema. Example: yaml `typeInfoDefaultImpls: {PostRegistrationRequest: PostRegistrationBasicRequest}`", "empty map");
         addSwitch(CodegenConstants.USE_ENUM_VALUE_INTERFACE, CodegenConstants.USE_ENUM_VALUE_INTERFACE_DESC, useEnumValueInterface);
         addSwitch(CodegenConstants.OPENAPI_NULLABLE,
                 "Enable OpenAPI Jackson Nullable library (jackson-databind-nullable) for optional + nullable "
@@ -585,6 +589,10 @@ public void processOpts() {
 
         convertPropertyToBooleanAndWriteBack(CodegenConstants.USE_DEDUCTION_FOR_ONE_OF_INTERFACES, this::setUseDeductionForOneOfInterfaces);
 
+        if (additionalProperties.containsKey(TYPE_INFO_DEFAULT_IMPLS)) {
+            typeInfoDefaultImpls.putAll(getPropertyAsStringMap(TYPE_INFO_DEFAULT_IMPLS));
+        }
+
         additionalProperties.put("springHttpStatus", new SpringHttpStatusLambda());
 
         // Set basePackage from invokerPackage
@@ -1319,6 +1327,36 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
 
         Map<String, CodegenModel> allModelsMap = getAllModels(objs);
 
+        // Resolve x-jackson-default-impl and typeInfoDefaultImpls into x-jackson-resolved-default-impl
+        // on each model. This drives defaultImpl = ... in @JsonTypeInfo for both deduction-based
+        // and discriminator-based oneOf interfaces.
+        for (CodegenModel cm : allModelsMap.values()) {
+            String schemaAnnotation = (String) cm.vendorExtensions.get("x-jackson-default-impl");
+            String configValue = typeInfoDefaultImpls.get(cm.schemaName);
+            String rawValue;
+            if (configValue != null && !configValue.isBlank()) {
+                if (schemaAnnotation != null && !schemaAnnotation.isBlank()) {
+                    LOGGER.warn("typeInfoDefaultImpls overrides x-jackson-default-impl on schema '{}': '{}' → '{}'",
+                            cm.schemaName, schemaAnnotation, configValue);
+                }
+                rawValue = configValue;
+            } else if (schemaAnnotation != null && !schemaAnnotation.isBlank()) {
+                rawValue = schemaAnnotation;
+            } else {
+                continue;
+            }
+            String resolved = toModelName(rawValue);
+            if (resolved != null && !resolved.isBlank()) {
+                cm.vendorExtensions.put("x-jackson-resolved-default-impl", resolved);
+                // When a discriminator is present, the typeInfoAnnotation partial is rendered
+                // inside {{#discriminator}}, so JMustache resolves 'vendorExtensions' against
+                // CodegenDiscriminator (not CodegenModel). Store there too.
+                if (cm.discriminator != null) {
+                    cm.discriminator.getVendorExtensions().put("x-jackson-resolved-default-impl", resolved);
+                }
+            }
+        }
+
         // For each oneOf interface with a discriminator, mark the discriminator property
         // as inherited in each subtype and set its default value from the discriminator mapping
         for (CodegenModel cm : allModelsMap.values()) {

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

@@ -123,6 +123,7 @@ public class SpringCodegen extends AbstractJavaCodegen
     public static final String GENERATE_PAGEABLE_CONSTRAINT_VALIDATION = "generatePageableConstraintValidation";
     public static final String SUBSTITUTE_GENERIC_PAGED_MODEL = "substituteGenericPagedModel";
     public static final String CLIENT_REGISTRATION_ID = "clientRegistrationId";
+    public static final String TYPE_INFO_DEFAULT_IMPLS = "typeInfoDefaultImpls";
 
     @Getter
     public enum RequestMappingMode {
@@ -201,6 +202,7 @@ public enum RequestMappingMode {
     protected String clientRegistrationId = null;
     @Setter protected boolean useEnumValueInterface = false;
     private String valuedEnumClassName = "ValuedEnum";
+    private Map<String, String> typeInfoDefaultImpls = new HashMap<>();
 
     // Map from schema name to detected paged-model info (populated when substituteGenericPagedModel=true)
     private Map<String, PagedModelScanUtils.DetectedPagedModel> pagedModelRegistry = new HashMap<>();
@@ -340,6 +342,7 @@ public SpringCodegen() {
                 optionalAcceptNullable));
 
         cliOptions.add(CliOption.newBoolean(USE_DEDUCTION_FOR_ONE_OF_INTERFACES, USE_DEDUCTION_FOR_ONE_OF_INTERFACES_DESC, useDeductionForOneOfInterfaces));
+        cliOptions.add(new CliOption(TYPE_INFO_DEFAULT_IMPLS, "Map of schema name to default Jackson deserialization class for @JsonTypeInfo(defaultImpl=...). Applies to both deduction-based and discriminator-based oneOf interfaces. Overrides x-jackson-default-impl when both are set for the same schema. Example: yaml `typeInfoDefaultImpls: {PostRegistrationRequest: PostRegistrationBasicRequest}`"));
         cliOptions.add(CliOption.newString(SPRING_API_VERSION, "Value for 'version' attribute in @RequestMapping (for Spring 7 and above)."));
         cliOptions.add(CliOption.newString(USE_HTTP_SERVICE_PROXY_FACTORY_INTERFACES_CONFIGURATOR,
             "Generate HttpInterfacesAbstractConfigurator based on an HttpServiceProxyFactory instance (as opposed to a WebClient instance, when disabled) for generating Spring HTTP interfaces.")
@@ -572,6 +575,10 @@ public void processOpts() {
         convertPropertyToBooleanAndWriteBack(OPTIONAL_ACCEPT_NULLABLE, this::setOptionalAcceptNullable);
         convertPropertyToBooleanAndWriteBack(USE_SPRING_BUILT_IN_VALIDATION, this::setUseSpringBuiltInValidation);
         convertPropertyToBooleanAndWriteBack(CodegenConstants.USE_DEDUCTION_FOR_ONE_OF_INTERFACES, this::setUseDeductionForOneOfInterfaces);
+
+        if (additionalProperties.containsKey(TYPE_INFO_DEFAULT_IMPLS)) {
+            typeInfoDefaultImpls.putAll(getPropertyAsStringMap(TYPE_INFO_DEFAULT_IMPLS));
+        }
         convertPropertyToStringAndWriteBack(CLIENT_REGISTRATION_ID, this::setClientRegistrationId);
 
         additionalProperties.put("springHttpStatus", new SpringHttpStatusLambda());
@@ -1421,6 +1428,37 @@ public Map<String, ModelsMap> postProcessAllModels(Map<String, ModelsMap> objs)
         objs = super.postProcessAllModels(objs);
 
         Map<String, CodegenModel> allModels = getAllModels(objs);
+
+        // Resolve x-jackson-default-impl and typeInfoDefaultImpls into x-jackson-resolved-default-impl
+        // on each model. This drives defaultImpl = ... in @JsonTypeInfo for both deduction-based
+        // and discriminator-based oneOf interfaces.
+        for (CodegenModel cm : allModels.values()) {
+            String schemaAnnotation = (String) cm.vendorExtensions.get("x-jackson-default-impl");
+            String configValue = typeInfoDefaultImpls.get(cm.schemaName);
+            String rawValue;
+            if (configValue != null && !configValue.isBlank()) {
+                if (schemaAnnotation != null && !schemaAnnotation.isBlank()) {
+                    LOGGER.warn("typeInfoDefaultImpls overrides x-jackson-default-impl on schema '{}': '{}' → '{}'",
+                            cm.schemaName, schemaAnnotation, configValue);
+                }
+                rawValue = configValue;
+            } else if (schemaAnnotation != null && !schemaAnnotation.isBlank()) {
+                rawValue = schemaAnnotation;
+            } else {
+                continue;
+            }
+            String resolved = toModelName(rawValue);
+            if (resolved != null && !resolved.isBlank()) {
+                cm.vendorExtensions.put("x-jackson-resolved-default-impl", resolved);
+                // When a discriminator is present, the typeInfoAnnotation partial is rendered
+                // inside {{#discriminator}}, so JMustache resolves 'vendorExtensions' against
+                // CodegenDiscriminator (not CodegenModel). Store there too.
+                if (cm.discriminator != null) {
+                    cm.discriminator.getVendorExtensions().put("x-jackson-resolved-default-impl", resolved);
+                }
+            }
+        }
+
         // conditionally force the generation of no args constructor
         for (CodegenModel cm : allModels.values()) {
             boolean hasLombokNoArgsConstructor = lombokAnnotations != null && lombokAnnotations.containsKey("NoArgsConstructor");

modules/openapi-generator/src/main/resources/JavaSpring/oneof_interface.mustache

@@ -7,7 +7,7 @@
 {{>typeInfoAnnotation}}
 
 {{/discriminator}}{{^discriminator}}{{#useDeductionForOneOfInterfaces}}
-@JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION)
+@JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION{{#vendorExtensions.x-jackson-resolved-default-impl}}, defaultImpl = {{vendorExtensions.x-jackson-resolved-default-impl}}.class{{/vendorExtensions.x-jackson-resolved-default-impl}})
 @JsonSubTypes({
     {{#interfaceModels}}
     @JsonSubTypes.Type(value = {{classname}}.class){{^-last}}, {{/-last}}

modules/openapi-generator/src/main/resources/JavaSpring/typeInfoAnnotation.mustache

@@ -6,10 +6,10 @@
   value = "{{{discriminator.propertyBaseName}}}", // ignore manually set {{{discriminator.propertyBaseName}}}, it will be automatically generated by Jackson during serialization
   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}})
 {{/disableDiscriminatorJsonIgnoreProperties}}
 {{#disableDiscriminatorJsonIgnoreProperties}}
-    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "{{{discriminator.propertyBaseName}}}", visible = true)
+    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_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}})
 {{/disableDiscriminatorJsonIgnoreProperties}}
 @JsonSubTypes({
 {{/-first}}

modules/openapi-generator/src/main/resources/kotlin-spring/oneof_interface.mustache

@@ -5,7 +5,7 @@
 {{>typeInfoAnnotation}}
 {{/discriminator}}
 {{^discriminator}}{{#useDeductionForOneOfInterfaces}}{{#jackson}}
-@JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION)
+@JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION{{#vendorExtensions.x-jackson-resolved-default-impl}}, defaultImpl = {{vendorExtensions.x-jackson-resolved-default-impl}}::class{{/vendorExtensions.x-jackson-resolved-default-impl}})
 @JsonSubTypes(
   {{#interfaceModels}}
     JsonSubTypes.Type(value = {{classname}}::class){{^-last}},{{/-last}}

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

@@ -3,7 +3,7 @@
   value = ["{{{discriminator.propertyBaseName}}}"], // ignore manually set {{{discriminator.propertyBaseName}}}, it will be automatically generated by Jackson during serialization
   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}}
       JsonSubTypes.Type(value = {{modelName}}::class, name = "{{^vendorExtensions.x-discriminator-value}}{{mappingName}}{{/vendorExtensions.x-discriminator-value}}{{#vendorExtensions.x-discriminator-value}}{{{vendorExtensions.x-discriminator-value}}}{{/vendorExtensions.x-discriminator-value}}"){{^-last}},{{/-last}}

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

@@ -8132,4 +8132,81 @@ void schemaMappingWithNullableAllOfRendersNullableJavaProperty() throws IOExcept
         JavaFileAssert.assertThat(files.get("MyObject.java"))
                 .assertProperty("optionalRef").withType("JsonNullable<com.example.ExternalModel>");
     }
+
+    // ========== x-jackson-default-impl / typeInfoDefaultImpls tests ==========
+
+    @Test(description = "x-jackson-default-impl on deduction schema emits defaultImpl in @JsonTypeInfo")
+    public void xJacksonDefaultImplOnDeductionSchemaEmitsDefaultImpl() throws IOException {
+        Map<String, Object> additionalProperties = new HashMap<>();
+        additionalProperties.put(USE_DEDUCTION_FOR_ONE_OF_INTERFACES, "true");
+
+        Map<String, File> files = generateFromContract(
+                "src/test/resources/3_0/spring/jackson-default-impl.yaml", SPRING_BOOT, additionalProperties);
+
+        JavaFileAssert.assertThat(files.get("Animal.java"))
+                .fileContains("@JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION, defaultImpl = Dog.class)");
+    }
+
+    @Test(description = "typeInfoDefaultImpls config option on deduction schema emits defaultImpl in @JsonTypeInfo")
+    public void typeInfoDefaultImplsConfigOptionOnDeductionSchemaEmitsDefaultImpl() throws IOException {
+        Map<String, Object> additionalProperties = new HashMap<>();
+        additionalProperties.put(USE_DEDUCTION_FOR_ONE_OF_INTERFACES, "true");
+        additionalProperties.put(TYPE_INFO_DEFAULT_IMPLS, Map.of("Animal", "Dog"));
+
+        Map<String, File> files = generateFromContract(
+                "src/test/resources/3_0/oneof_polymorphism_and_inheritance.yaml", SPRING_BOOT, additionalProperties);
+
+        JavaFileAssert.assertThat(files.get("Animal.java"))
+                .fileContains("@JsonTypeInfo(use = JsonTypeInfo.Id.DEDUCTION, defaultImpl = Dog.class)");
+    }
+
+    @Test(description = "typeInfoDefaultImpls overrides x-jackson-default-impl on deduction schema")
+    public void typeInfoDefaultImplsOverridesSchemaAnnotationOnDeductionSchema() throws IOException {
+        Map<String, Object> additionalProperties = new HashMap<>();
+        additionalProperties.put(USE_DEDUCTION_FOR_ONE_OF_INTERFACES, "true");
+        // Override x-jackson-default-impl: Dog (set in YAML) with Cat via config option
+        additionalProperties.put(TYPE_INFO_DEFAULT_IMPLS, Map.of("Animal", "Cat"));
+
+        Map<String, File> files = generateFromContract(
+                "src/test/resources/3_0/spring/jackson-default-impl.yaml", SPRING_BOOT, additionalProperties);
+
+        JavaFileAssert.assertThat(files.get("Animal.java"))
+                .fileContains("defaultImpl = Cat.class")
+                .fileDoesNotContain("defaultImpl = Dog.class");
+    }
+
+    @Test(description = "x-jackson-default-impl on discriminator schema emits defaultImpl in @JsonTypeInfo")
+    public void xJacksonDefaultImplOnDiscriminatorSchemaEmitsDefaultImpl() throws IOException {
+        Map<String, File> files = generateFromContract(
+                "src/test/resources/3_0/spring/jackson-default-impl.yaml", SPRING_BOOT, new HashMap<>());
+
+        JavaFileAssert.assertThat(files.get("Fruit.java"))
+                .fileContains("defaultImpl = Apple.class");
+    }
+
+    @Test(description = "no defaultImpl when neither x-jackson-default-impl nor typeInfoDefaultImpls is set")
+    public void noDefaultImplWhenNeitherSourceIsSet() throws IOException {
+        Map<String, Object> additionalProperties = new HashMap<>();
+        additionalProperties.put(USE_DEDUCTION_FOR_ONE_OF_INTERFACES, "true");
+
+        Map<String, File> files = generateFromContract(
+                "src/test/resources/3_0/oneof_polymorphism_and_inheritance.yaml", SPRING_BOOT, additionalProperties);
+
+        JavaFileAssert.assertThat(files.get("Animal.java"))
+                .fileDoesNotContain("defaultImpl");
+    }
+
+    @Test(description = "typeInfoDefaultImpls applies model name suffix to resolved default impl")
+    public void typeInfoDefaultImplsAppliesModelNameSuffix() throws IOException {
+        Map<String, Object> additionalProperties = new HashMap<>();
+        additionalProperties.put(USE_DEDUCTION_FOR_ONE_OF_INTERFACES, "true");
+        additionalProperties.put(TYPE_INFO_DEFAULT_IMPLS, Map.of("Animal", "Dog"));
+        additionalProperties.put(MODEL_NAME_SUFFIX, "Dto");
+
+        Map<String, File> files = generateFromContract(
+                "src/test/resources/3_0/oneof_polymorphism_and_inheritance.yaml", SPRING_BOOT, additionalProperties);
+
+        JavaFileAssert.assertThat(files.get("AnimalDto.java"))
+                .fileContains("defaultImpl = DogDto.class");
+    }
 }