aws · zoewangg · Aug 7, 2026
@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "AWS SDK for Java v2",
+    "contributor": "",
+    "description": "Reduce generated client source and bytecode size for JSON, CBOR, and Smithy RPC v2 protocol services by generating the error-metadata mapper once per client instead of once per operation."
+}
@@ -152,6 +152,8 @@ protected void addFields(Builder type) {
             .addField(protocolSpec.protocolFactory(model))
             .addField(SdkClientConfiguration.class, "clientConfiguration", PRIVATE, FINAL);
 
+        protocolSpec.errorResponseMapperField().ifPresent(type::addField);
+
         // Kinesis doesn't support CBOR for STS yet so need another protocol factory for JSON
         if (model.getMetadata().isCborProtocol()) {
             type.addField(AwsJsonProtocolFactory.class, "jsonProtocolFactory", PRIVATE, FINAL);

@@ -129,6 +129,7 @@ protected void addFields(TypeSpec.Builder type) {
             .addField(SyncClientHandler.class, "clientHandler", PRIVATE, FINAL)
             .addField(protocolSpec.protocolFactory(model))
             .addField(SdkClientConfiguration.class, "clientConfiguration", PRIVATE, FINAL);
+        protocolSpec.errorResponseMapperField().ifPresent(type::addField);
     }
 
     @Override

@@ -168,39 +168,48 @@ public Optional<CodeBlock> errorResponseHandler(OperationModel opModel) {
         String protocolFactory = protocolFactoryLiteral(model, opModel);
 
         CodeBlock.Builder builder = CodeBlock.builder();
+        builder.add("\n$T<$T> errorResponseHandler = createErrorResponseHandler($L, operationMetadata, "
+                    + "exceptionMetadataMapper);",
+                    HttpResponseHandler.class, AwsServiceException.class, protocolFactory);
+
+        return Optional.of(builder.build());
+    }
+
+    @Override
+    public Optional<FieldSpec> errorResponseMapperField() {
         ParameterizedTypeName metadataMapperType = ParameterizedTypeName.get(
             ClassName.get(Function.class),
             ClassName.get(String.class),
             ParameterizedTypeName.get(Optional.class, ExceptionMetadata.class));
 
-        builder.add("\n$T exceptionMetadataMapper = errorCode -> {\n", metadataMapperType);
-        builder.add("if (errorCode == null) {\n");
-        builder.add("return $T.empty();\n", Optional.class);
-        builder.add("}\n");
-        builder.add("switch (errorCode) {\n");
+        CodeBlock.Builder initializer = CodeBlock.builder();
+        initializer.add("errorCode -> {\n");
+        initializer.add("if (errorCode == null) {\n");
+        initializer.add("return $T.empty();\n", Optional.class);
+        initializer.add("}\n");
+        initializer.add("switch (errorCode) {\n");
         model.getShapes().values().stream()
              .filter(shape -> shape.getShapeType() == ShapeType.Exception)
              .forEach(exceptionShape -> {
-                 String exceptionName = exceptionShape.getShapeName();
                  String errorCode = exceptionShape.getErrorCode();
 
-                 builder.add("case $S:\n", errorCode);
-                 builder.add("return $T.of($T.builder()\n", Optional.class, ExceptionMetadata.class)
-                        .add(".errorCode($S)\n", errorCode);
-                 builder.add(populateHttpStatusCode(exceptionShape, model));
-                 builder.add(".exceptionBuilderSupplier($T::builder)\n",
-                             poetExtensions.getModelClassFromShape(exceptionShape))
-                        .add(".build());\n");
+                 initializer.add("case $S:\n", errorCode);
+                 initializer.add("return $T.of($T.builder()\n", Optional.class, ExceptionMetadata.class)
+                            .add(".errorCode($S)\n", errorCode);
+                 initializer.add(populateHttpStatusCode(exceptionShape, model));
+                 initializer.add(".exceptionBuilderSupplier($T::builder)\n",
+                                 poetExtensions.getModelClassFromShape(exceptionShape))
+                            .add(".build());\n");
              });
 
-        builder.add("default: return $T.empty();\n", Optional.class);
-        builder.add("}\n");
-        builder.add("};\n");
-
-        builder.add("$T<$T> errorResponseHandler = createErrorResponseHandler($L, operationMetadata, exceptionMetadataMapper);",
-                    HttpResponseHandler.class, AwsServiceException.class, protocolFactory);
+        initializer.add("default: return $T.empty();\n", Optional.class);
+        initializer.add("}\n");
+        initializer.add("}");
 
-        return Optional.of(builder.build());
+        return Optional.of(FieldSpec.builder(metadataMapperType, "exceptionMetadataMapper",
+                                             Modifier.PRIVATE, Modifier.FINAL)
+                                    .initializer(initializer.build())
+                                    .build());
     }
 
     @Override

@@ -70,6 +70,15 @@ default Optional<MethodSpec> createEventstreamErrorResponseHandler() {
         return Optional.empty();
     }
 
+    /**
+     * The per-client field holding the non-streaming {@code exceptionMetadataMapper}, when the protocol emits one. The
+     * mapper switches over the whole model's exceptions and is identical for every operation, so it is generated once as
+     * a client field instead of once per operation body.
+     */
+    default Optional<FieldSpec> errorResponseMapperField() {
+        return Optional.empty();
+    }
+
     default List<MethodSpec> additionalMethods() {
         return new ArrayList<>();
     }

@@ -41,25 +41,22 @@ public class ClientLambdaCallSiteCeilingTest {
      * fixture's count by its operation count, which is at least 4 for every fixture listed here, so the headroom absorbs
      * a couple of new shared per-client lambdas without absorbing a per-operation one. Single-operation fixtures are
      * excluded for that reason: no headroom smaller than one operation exists.
-     *
-     * <p>The JSON, CBOR and Smithy RPC v2 fixtures are legitimately higher than the rest because those protocols emit a
-     * per-operation {@code exceptionMetadataMapper} lambda whose body switches over that operation's error codes.
      */
     private static Stream<Arguments> ceilings() {
         return Stream.of(
-            Arguments.of("test-json-async-client-class.java", 44),
-            Arguments.of("test-json-client-class.java", 18),
-            Arguments.of("test-aws-json-async-client-class.java", 38),
-            Arguments.of("test-cbor-async-client-class.java", 38),
-            Arguments.of("test-cbor-client-class.java", 16),
-            Arguments.of("test-rpcv2-async-client-class.java", 19),
-            Arguments.of("test-rpcv2-sync.java", 18),
+            Arguments.of("test-json-async-client-class.java", 29),
+            Arguments.of("test-json-client-class.java", 6),
+            Arguments.of("test-aws-json-async-client-class.java", 25),
+            Arguments.of("test-cbor-async-client-class.java", 25),
+            Arguments.of("test-cbor-client-class.java", 6),
+            Arguments.of("test-rpcv2-async-client-class.java", 7),
+            Arguments.of("test-rpcv2-sync.java", 6),
             Arguments.of("test-query-async-client-class.java", 14),
             Arguments.of("test-query-client-class.java", 5),
             Arguments.of("test-xml-async-client-class.java", 18),
             Arguments.of("test-xml-client-class.java", 5),
-            Arguments.of("test-unsigned-payload-trait-async-client-class.java", 17),
-            Arguments.of("test-unsigned-payload-trait-sync-client-class.java", 16)
+            Arguments.of("test-unsigned-payload-trait-async-client-class.java", 7),
+            Arguments.of("test-unsigned-payload-trait-sync-client-class.java", 6)
         );
     }