fix(java): batch Gson model adapter registration

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

@@ -66,6 +66,7 @@ public class JavaClientCodegen extends AbstractJavaCodegen
         implements BeanValidationFeatures, PerformBeanValidationFeatures, GzipFeatures {
 
     static final String MEDIA_TYPE = "mediaType";
+    private static final int GSON_ADAPTERS_PER_BATCH = 200;
 
     private final Logger LOGGER = LoggerFactory.getLogger(JavaClientCodegen.class);
 
@@ -1415,6 +1416,31 @@ public void forceSerializationLibrary(String serializationLibrary) {
     @Override
     public Map<String, Object> postProcessSupportingFileData(Map<String, Object> objs) {
         generateYAMLSpecFile(objs);
+        if (isLibrary(OKHTTP_GSON)) {
+            // Match the models registered by JSON.mustache, preserving their generation order.
+            @SuppressWarnings("unchecked")
+            List<ModelMap> models = (List<ModelMap>) objs.get("models");
+            List<CodegenModel> adapters = new ArrayList<>();
+            if (models != null) {
+                for (ModelMap model : models) {
+                    CodegenModel m = model.getModel();
+                    if (m != null && !m.isEnum && !m.hasChildren) {
+                        adapters.add(m);
+                    }
+                }
+            }
+            // Large initializers can exceed the JVM method-size limit; register in bounded batches.
+            if (adapters.size() > GSON_ADAPTERS_PER_BATCH) {
+                List<Map<String, Object>> batches = new ArrayList<>();
+                for (int i = 0; i < adapters.size(); i += GSON_ADAPTERS_PER_BATCH) {
+                    Map<String, Object> batch = new HashMap<>();
+                    batch.put("index", batches.size());
+                    batch.put("models", adapters.subList(i, Math.min(i + GSON_ADAPTERS_PER_BATCH, adapters.size())));
+                    batches.add(batch);
+                }
+                objs.put("gsonAdapterBatches", batches);
+            }
+        }
         return super.postProcessSupportingFileData(objs);
     }
 

modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/JSON.mustache

@@ -117,6 +117,14 @@ public class JSON {
         return clazz;
     }
 
+    {{#gsonAdapterBatches}}
+    private static void registerModelAdapters{{index}}(GsonBuilder gsonBuilder) {
+        {{#models}}
+        gsonBuilder.registerTypeAdapterFactory(new {{modelPackage}}.{{{classname}}}.CustomTypeAdapterFactory());
+        {{/models}}
+    }
+
+    {{/gsonAdapterBatches}}
     static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
@@ -131,6 +139,10 @@ public class JSON {
         gsonBuilder.registerTypeAdapter(LocalDateTime.class, localDateTimeTypeAdapter);
         {{/jsr310}}
         gsonBuilder.registerTypeAdapter(byte[].class, byteArrayAdapter);
+        {{#gsonAdapterBatches}}
+        registerModelAdapters{{index}}(gsonBuilder);
+        {{/gsonAdapterBatches}}
+        {{^gsonAdapterBatches}}
         {{#models}}
         {{#model}}
         {{^isEnum}}
@@ -140,6 +152,7 @@ public class JSON {
         {{/isEnum}}
         {{/model}}
         {{/models}}
+        {{/gsonAdapterBatches}}
         gson = gsonBuilder.create();
     }
 

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

@@ -81,6 +81,33 @@ public class JavaClientCodegenTest {
 
     private static final String JAVA_GENERATOR = "java";
 
+    @Test
+    @SneakyThrows
+    public void testOkHttpGsonBatchesModelAdapterRegistrations() {
+        Path output = newTempFolder();
+        Path spec = output.resolve("many-models.yaml");
+        StringBuilder yaml = new StringBuilder("openapi: 3.0.0\ninfo: {title: Batch test, version: '1'}\npaths: {}\ncomponents:\n  schemas:\n");
+        for (int i = 0; i < 201; i++) {
+            yaml.append("    Model").append(i).append(":\n      type: object\n      properties:\n        value: {type: string}\n");
+        }
+        Files.write(spec, yaml.toString().getBytes(StandardCharsets.UTF_8));
+        CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName(JAVA_GENERATOR)
+                .setLibrary(OKHTTP_GSON)
+                .setInputSpec(spec.toString())
+                .setOutputDir(output.toString());
+        new DefaultGenerator().opts(configurator.toClientOptInput()).generate();
+        Path json = output.resolve("src/main/java/org/openapitools/client/JSON.java");
+        String code = new String(Files.readAllBytes(json), StandardCharsets.UTF_8);
+        StaticJavaParser.parse(code);
+        assertThat(code).contains("private static void registerModelAdapters0(GsonBuilder gsonBuilder)",
+                "private static void registerModelAdapters1(GsonBuilder gsonBuilder)",
+                "registerModelAdapters0(gsonBuilder);", "registerModelAdapters1(gsonBuilder);");
+        for (int i = 0; i < 201; i++) {
+            assertThat(code).containsOnlyOnce("new org.openapitools.client.model.Model" + i + ".CustomTypeAdapterFactory()");
+        }
+    }
+
     // This is the kind of information that ideally would be defined and available system-wide
     @Getter
     enum Library {