Simplify generated error unmarshalling code in json protocol based clients

.changes/next-release/bugfix-AWSSDKforJavav2-5e43973.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "AWS SDK for Java v2",
+    "contributor": "apache-hb",
+    "description": "Simplify generated error unmarshalling code in json protocol based clients."
+}

codegen/src/main/java/software/amazon/awssdk/codegen/poet/client/AsyncClientClass.java

@@ -172,6 +172,7 @@ protected void addAdditionalMethods(TypeSpec.Builder type) {
                                                           model));
         protocolSpec.createErrorResponseHandler().ifPresent(type::addMethod);
         protocolSpec.createEventstreamErrorResponseHandler().ifPresent(type::addMethod);
+        protocolSpec.errorResponseHandlerProvider(model).ifPresent(type::addMethod);
     }
 
     @Override
@@ -331,10 +332,10 @@ protected MethodSpec.Builder operationBody(MethodSpec.Builder builder, Operation
                              CoreMetric.class, "SERVICE_ID", model.getMetadata().getServiceId());
         builder.addStatement("apiCallMetricCollector.reportMetric($T.$L, $S)",
                              CoreMetric.class, "OPERATION_NAME", opModel.getOperationName());
-        
+
         if (opModel.hasStreamingOutput()) {
             ClassName responseType = poetExtensions.getModelClass(opModel.getReturnType().getReturnType());
-            
+
             builder.addStatement("$T<$T<$T, ReturnT>, $T<$T>> $N = $T.wrapWithEndOfStreamFuture($N)",
                                  Pair.class,
                                  AsyncResponseTransformer.class,
@@ -344,11 +345,11 @@ protected MethodSpec.Builder operationBody(MethodSpec.Builder builder, Operation
                                  "pair",
                                  AsyncResponseTransformerUtils.class,
                                  "asyncResponseTransformer");
-            
+
             builder.addStatement("$N = $N.left()",
                                  "asyncResponseTransformer",
                                  "pair");
-            
+
             builder.addStatement("$T<$T> $N = $N.right()",
                                  CompletableFuture.class,
                                  Void.class,

codegen/src/main/java/software/amazon/awssdk/codegen/poet/client/SyncClientClass.java

@@ -140,6 +140,8 @@ protected void addAdditionalMethods(TypeSpec.Builder type) {
         type.addMethod(updateSdkClientConfigurationMethod(configurationUtils.serviceClientConfigurationBuilderClassName(),
                                                           model));
         type.addMethod(protocolSpec.initProtocolFactory(model));
+
+        protocolSpec.errorResponseHandlerProvider(model).ifPresent(type::addMethod);
     }
 
     private FieldSpec logger() {

codegen/src/main/java/software/amazon/awssdk/codegen/poet/client/specs/JsonProtocolSpec.java

@@ -16,6 +16,7 @@
 package software.amazon.awssdk.codegen.poet.client.specs;
 
 import static software.amazon.awssdk.codegen.model.intermediate.Protocol.AWS_JSON;
+import static javax.lang.model.element.Modifier.PRIVATE;
 
 import com.squareup.javapoet.ClassName;
 import com.squareup.javapoet.CodeBlock;
@@ -167,12 +168,18 @@ public Optional<CodeBlock> errorResponseHandler(OperationModel opModel) {
         String protocolFactory = protocolFactoryLiteral(model, opModel);
 
         CodeBlock.Builder builder = CodeBlock.builder();
-        ParameterizedTypeName metadataMapperType = ParameterizedTypeName.get(
-            ClassName.get(Function.class),
-            ClassName.get(String.class),
-            ParameterizedTypeName.get(Optional.class, ExceptionMetadata.class));
 
-        builder.add("\n$T exceptionMetadataMapper = errorCode -> {\n", metadataMapperType);
+        builder.add("$T<$T> errorResponseHandler = createErrorResponseHandler($L, operationMetadata, this::exceptionMetadataMapper);",
+                    HttpResponseHandler.class, AwsServiceException.class, protocolFactory);
+
+        return Optional.of(builder.build());
+    }
+
+    @Override
+    public Optional<MethodSpec> errorResponseHandlerProvider(IntermediateModel model) {
+
+        CodeBlock.Builder builder = CodeBlock.builder();
+
         builder.add("if (errorCode == null) {\n");
         builder.add("return $T.empty();\n", Optional.class);
         builder.add("}\n");
@@ -194,12 +201,13 @@ public Optional<CodeBlock> errorResponseHandler(OperationModel opModel) {
 
         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);
 
-        return Optional.of(builder.build());
+        MethodSpec.Builder method = MethodSpec.methodBuilder("exceptionMetadataMapper")
+                                    .addModifiers(PRIVATE)
+                                    .addParameter(String.class, "errorCode")
+                                    .addCode(builder.build())
+                                    .returns(ParameterizedTypeName.get(Optional.class, ExceptionMetadata.class));
+        return Optional.of(method.build());
     }
 
     @Override

codegen/src/main/java/software/amazon/awssdk/codegen/poet/client/specs/ProtocolSpec.java

@@ -51,6 +51,10 @@ public interface ProtocolSpec {
 
     Optional<CodeBlock> errorResponseHandler(OperationModel opModel);
 
+    default Optional<MethodSpec> errorResponseHandlerProvider(IntermediateModel model) {
+        return Optional.empty();
+    }
+
     CodeBlock executionHandler(OperationModel opModel);
 
     /**