feat(kotlin-spring): default to Jackson 3 when Spring Boot 4 is enabled

Spring Boot 4 ships with Jackson 3 out of the box, so useJackson3 now
defaults to true when useSpringBoot4 is enabled and the user hasn't
explicitly set useJackson3.

Author: yonatankarp

docs/generators/kotlin-spring.md

@@ -58,7 +58,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |useBeanValidation|Use BeanValidation API annotations to validate data types| |true|
 |useFeignClientUrl|Whether to generate Feign client with url parameter.| |true|
 |useFlowForArrayReturnType|Whether to use Flow for array/collection return types when reactive is enabled. If false, will use List instead.| |true|
-|useJackson3|Use Jackson 3 dependencies (tools.jackson package). Only available with `useSpringBoot4`. Incompatible with `openApiNullable`.| |false|
+|useJackson3|Use Jackson 3 dependencies (tools.jackson package). Only available with `useSpringBoot4`. Defaults to true when `useSpringBoot4` is enabled. Incompatible with `openApiNullable`.| |false|
 |useResponseEntity|Whether (when false) to return actual type (e.g. List<Fruit>) and handle non-happy path responses via exceptions flow or (when true) return entire ResponseEntity (e.g. ResponseEntity<List<Fruit>>). If disabled, method are annotated using a @ResponseStatus annotation, which has the status of the first response declared in the Api definition| |true|
 |useSealedResponseInterfaces|Generate sealed interfaces for endpoint responses that all possible response types implement. Allows controllers to return any valid response type in a type-safe manner (e.g., sealed interface CreateUserResponse implemented by User, ConflictResponse, ErrorResponse)| |false|
 |useSpringBoot3|Generate code and provide dependencies for use with Spring Boot ≥ 3 (use jakarta instead of javax in imports). Enabling this option will also enable `useJakartaEe`.| |false|

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

@@ -256,7 +256,7 @@ public KotlinSpringServerCodegen() {
                 " (contexts) added to single project.", beanQualifiers);
         addSwitch(USE_SPRING_BOOT3, "Generate code and provide dependencies for use with Spring Boot ≥ 3 (use jakarta instead of javax in imports). Enabling this option will also enable `useJakartaEe`.", useSpringBoot3);
         addSwitch(USE_SPRING_BOOT4, "Generate code and provide dependencies for use with Spring Boot 4.x. Enabling this option will also enable `useJakartaEe`.", useSpringBoot4);
-        addSwitch(USE_JACKSON_3, "Use Jackson 3 dependencies (tools.jackson package). Only available with `useSpringBoot4`. Incompatible with `openApiNullable`.", useJackson3);
+        addSwitch(USE_JACKSON_3, "Use Jackson 3 dependencies (tools.jackson package). Only available with `useSpringBoot4`. Defaults to true when `useSpringBoot4` is enabled. Incompatible with `openApiNullable`.", useJackson3);
         addSwitch(USE_FLOW_FOR_ARRAY_RETURN_TYPE, "Whether to use Flow for array/collection return types when reactive is enabled. If false, will use List instead.", useFlowForArrayReturnType);
         addSwitch(INCLUDE_HTTP_REQUEST_CONTEXT, "Whether to include HttpServletRequest (blocking) or ServerWebExchange (reactive) as additional parameter in generated methods.", includeHttpRequestContext);
         addSwitch(USE_RESPONSE_ENTITY,
@@ -421,6 +421,12 @@ public String getHelp() {
 
     @Override
     public void processOpts() {
+        if (additionalProperties.containsKey(USE_SPRING_BOOT4)
+                && Boolean.parseBoolean(additionalProperties.get(USE_SPRING_BOOT4).toString())
+                && !additionalProperties.containsKey(USE_JACKSON_3)) {
+            additionalProperties.put(USE_JACKSON_3, "true");
+        }
+
         super.processOpts();
 
         if (DocumentationProvider.SPRINGFOX.equals(getDocumentationProvider())) {

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

@@ -4874,6 +4874,38 @@ public void shouldGenerateSpringBoot4PomWithJackson2Deps() throws IOException {
         assertFileNotContains(pomPath, "tools.jackson.dataformat");
         assertFileNotContains(pomPath, "tools.jackson.module");
     }
+
+    @Test
+    public void shouldDefaultToJackson3WhenSpringBoot4Enabled() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+        String outputPath = output.getAbsolutePath().replace('\\', '/');
+
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/petstore.yaml");
+        final KotlinSpringServerCodegen codegen = new KotlinSpringServerCodegen();
+        codegen.setOpenAPI(openAPI);
+        codegen.setOutputDir(output.getAbsolutePath());
+
+        codegen.additionalProperties().put(KotlinSpringServerCodegen.USE_SPRING_BOOT4, "true");
+        // useJackson3 is NOT set — should default to true
+        codegen.additionalProperties().put(DOCUMENTATION_PROVIDER, DocumentationProvider.NONE.toCliOptValue());
+        codegen.additionalProperties().put(ANNOTATION_LIBRARY, AnnotationLibrary.NONE.toCliOptValue());
+
+        ClientOptInput input = new ClientOptInput();
+        input.openAPI(openAPI);
+        input.config(codegen);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        generator.setGenerateMetadata(false);
+        generator.opts(input).generate();
+
+        Path pomPath = Paths.get(outputPath + "/pom.xml");
+        assertFileContains(pomPath, "tools.jackson.dataformat");
+        assertFileContains(pomPath, "tools.jackson.module");
+        assertFileNotContains(pomPath, "com.fasterxml.jackson.dataformat");
+        assertFileNotContains(pomPath, "com.fasterxml.jackson.module");
+        assertFileNotContains(pomPath, "jackson-datatype-jsr310");
+    }
 }