GH-3772 Add Protobuf transformation support

Fixes https://github.com/spring-projects/spring-integration/issues/3772

* Add basic To/From Protocol Buffer's com.google.protobuf.Message transformers.
* Allow the proto_type header to specify the type.
* Add tests.
* add Protobuf docs
* Leverage the Spring ProtobufMessageConverter
* move protobuf-java-util to test dependecies as optional
* protobuf docs improvements
* improve the expected type handling
* expected type expression
* fix indentation
* fix indentation for generated test classes
* suppress style check for proto generated classes
* address the transformer doc format
* fix whats new merge conflict
* fix doc sample code
* Some code clean up; fixing typos

.gitignore

@@ -31,3 +31,4 @@ vf.gf.dmn-*
 hostkey.ser
 .springBeans
 .sts4-cache
+.vscode/

build.gradle

@@ -94,6 +94,7 @@ ext {
     mysqlVersion = '8.0.32'
     pahoMqttClientVersion = '1.2.5'
     postgresVersion = '42.5.4'
+    protobufVersion = '3.21.12'
     r2dbch2Version = '1.0.0.RELEASE'
     reactorVersion = '2022.0.3'
     resilience4jVersion = '2.0.2'
@@ -542,7 +543,7 @@ project('spring-integration-core') {
         optionalApi('com.fasterxml.jackson.module:jackson-module-kotlin') {
             exclude group: 'org.jetbrains.kotlin'
         }
-
+        optionalApi "com.google.protobuf:protobuf-java:$protobufVersion"
         optionalApi "com.jayway.jsonpath:json-path:$jsonpathVersion"
         optionalApi "com.esotericsoftware:kryo:$kryoVersion"
         optionalApi 'io.micrometer:micrometer-core'
@@ -553,6 +554,7 @@ project('spring-integration-core') {
         optionalApi "org.apache.avro:avro:$avroVersion"
         optionalApi 'org.jetbrains.kotlinx:kotlinx-coroutines-reactor'
 
+        testImplementation "com.google.protobuf:protobuf-java-util:$protobufVersion"
         testImplementation "org.aspectj:aspectjweaver:$aspectjVersion"
         testImplementation 'io.micrometer:micrometer-observation-test'
         testImplementation ('io.micrometer:micrometer-tracing-integration-test') {

spring-integration-core/src/main/java/org/springframework/integration/transformer/FromProtobufTransformer.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.transformer;
+
+import org.springframework.beans.factory.BeanClassLoaderAware;
+import org.springframework.expression.EvaluationContext;
+import org.springframework.expression.Expression;
+import org.springframework.integration.context.IntegrationContextUtils;
+import org.springframework.integration.expression.FunctionExpression;
+import org.springframework.integration.expression.ValueExpression;
+import org.springframework.integration.transformer.support.ProtoHeaders;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.converter.ProtobufMessageConverter;
+import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
+
+/**
+ * A Protocol Buffer transformer to instantiate {@link com.google.protobuf.Message} objects
+ * from either {@code byte[]} if content type is {@code application/x-protobuf}
+ * or from {@code String} in case of {@code application/json} content type.
+ *
+ * @author Christian Tzolov
+ *
+ * @since 6.1
+ */
+public class FromProtobufTransformer extends AbstractTransformer implements BeanClassLoaderAware {
+
+	private final ProtobufMessageConverter protobufMessageConverter;
+
+	private ClassLoader beanClassLoader;
+
+	private Expression expectedTypeExpression =
+			new FunctionExpression<Message<?>>((message) -> message.getHeaders().get(ProtoHeaders.TYPE));
+
+	private EvaluationContext evaluationContext;
+
+	/**
+	 * Construct an instance with the supplied default type to create.
+	 */
+	public FromProtobufTransformer() {
+		this(new ProtobufMessageConverter());
+	}
+
+	/**
+	 * Construct an instance with the supplied default type and ProtobufMessageConverter instance.
+	 * @param protobufMessageConverter the message converter used.
+	 */
+	public FromProtobufTransformer(ProtobufMessageConverter protobufMessageConverter) {
+		Assert.notNull(protobufMessageConverter, "'protobufMessageConverter' must not be null");
+		this.protobufMessageConverter = protobufMessageConverter;
+	}
+
+	@Override
+	public void setBeanClassLoader(ClassLoader classLoader) {
+		this.beanClassLoader = classLoader;
+	}
+
+	/**
+	 * Set an expected protobuf class type.
+	 * Mutually exclusive with {@link #setExpectedTypeExpression} and
+	 * {@link #setExpectedTypeExpressionString}.
+	 * @param expectedType expected protobuf class type.
+	 * @return updated FromProtobufTransformer instance.
+	 */
+	public FromProtobufTransformer setExpectedType(Class<? extends com.google.protobuf.Message> expectedType) {
+		return setExpectedTypeExpression(new ValueExpression<>(expectedType));
+	}
+
+	/**
+	 * Set an expression to evaluate against the message to determine the type id.
+	 * Defaults to{@code headers['proto_type']}. Mutually exclusive with
+	 * {@link #setExpectedType} and {@link #setExpectedTypeExpression}.
+	 * @param expression the expression.
+	 * @return updated FromProtobufTransformer instance.
+	 */
+	public FromProtobufTransformer setExpectedTypeExpressionString(String expression) {
+		return setExpectedTypeExpression(EXPRESSION_PARSER.parseExpression(expression));
+	}
+
+	/**
+	 * Set an expression to evaluate against the message to determine the type.
+	 * Default {@code headers['proto_type']}.
+	 * Mutually exclusive with {@link #setExpectedType} and
+	 * {@link #setExpectedTypeExpressionString}.
+	 * @param expression the expression.
+	 * @return updated FromProtobufTransformer instance.
+	 */
+	public FromProtobufTransformer setExpectedTypeExpression(Expression expression) {
+		Assert.notNull(expression, "'expression' must not be null");
+		this.expectedTypeExpression = expression;
+		return this;
+	}
+
+	@Override
+	protected void onInit() {
+		this.evaluationContext = IntegrationContextUtils.getEvaluationContext(getBeanFactory());
+	}
+
+	@SuppressWarnings("unchecked")
+	@Override
+	protected Object doTransform(Message<?> message) {
+		Class<? extends com.google.protobuf.Message> targetClass = null;
+		Object value = this.expectedTypeExpression.getValue(this.evaluationContext, message);
+		if (value instanceof Class<?>) {
+			targetClass = (Class<? extends com.google.protobuf.Message>) value;
+		}
+		else if (value instanceof String) {
+			try {
+				targetClass =
+						(Class<? extends com.google.protobuf.Message>)
+								ClassUtils.forName((String) value, this.beanClassLoader);
+			}
+			catch (ClassNotFoundException | LinkageError e) {
+				throw new IllegalStateException(e);
+			}
+		}
+
+		if (targetClass == null) {
+			throw new MessageTransformationException(message,
+					"The 'expectedTypeExpression' (" + this.expectedTypeExpression + ") returned 'null'.");
+		}
+
+		return this.protobufMessageConverter.fromMessage(message, targetClass);
+	}
+
+}

spring-integration-core/src/main/java/org/springframework/integration/transformer/ToProtobufTransformer.java

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.transformer;
+
+import org.springframework.integration.transformer.support.ProtoHeaders;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.converter.ProtobufMessageConverter;
+import org.springframework.messaging.support.MessageHeaderAccessor;
+import org.springframework.util.Assert;
+
+/**
+ * A Protocol Buffer transformer for generated {@link com.google.protobuf.Message} objects.
+ * <p>
+ * If the content type is set to {@code application/x-protobuf} (default if no content type),
+ * then the output message payload is of type byte array.
+ * <p>
+ * If the content type is set to {@code application/json} and
+ * the {@code com.google.protobuf:protobuf-java-util} dependency is on the
+ * classpath, the output message payload if of type String.
+ *
+ * @author Christian Tzolov
+ *
+ * @since 6.1
+ */
+public class ToProtobufTransformer extends AbstractTransformer {
+
+	private final ProtobufMessageConverter protobufMessageConverter;
+
+	public ToProtobufTransformer() {
+		this(new ProtobufMessageConverter());
+	}
+
+	public ToProtobufTransformer(ProtobufMessageConverter protobufMessageConverter) {
+		Assert.notNull(protobufMessageConverter, "'protobufMessageConverter' must not be null");
+		this.protobufMessageConverter = protobufMessageConverter;
+	}
+
+	@Override
+	protected Object doTransform(Message<?> message) {
+		Assert.isInstanceOf(com.google.protobuf.Message.class, message.getPayload(),
+				"Payload must be an implementation of 'com.google.protobuf.Message'");
+
+		MessageHeaderAccessor accessor = new MessageHeaderAccessor(message);
+		accessor.setHeader(ProtoHeaders.TYPE, message.getPayload().getClass().getName());
+		if (!message.getHeaders().containsKey(MessageHeaders.CONTENT_TYPE)) {
+			accessor.setContentType(ProtobufMessageConverter.PROTOBUF);
+		}
+
+		return this.protobufMessageConverter.toMessage(message.getPayload(), accessor.getMessageHeaders());
+	}
+
+}

spring-integration-core/src/main/java/org/springframework/integration/transformer/support/ProtoHeaders.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.transformer.support;
+
+/**
+ * Pre-defined names and prefixes for Protocol Buffers related headers.
+ *
+ * @author Christian Tzolov
+ *
+ * @since 6.1
+ */
+public final class ProtoHeaders {
+
+	private ProtoHeaders() {
+	}
+
+	/**
+	 * The prefix for Protocol Buffers specific message headers.
+	 */
+	public static final String PREFIX = "proto_";
+
+	/**
+	 * The {@code com.google.protobuf.Message} type. By default, it's the fully qualified
+	 * {@code com.google.protobuf.Message} type but can be a key that is mapped to the actual type.
+	 */
+	public static final String TYPE = PREFIX + "type";
+
+}

spring-integration-core/src/test/java/org/springframework/integration/transformer/ProtoTests.java

@@ -0,0 +1,240 @@
+/*
+ * Copyright 2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.transformer;
+
+import java.util.Collections;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.integration.channel.DirectChannel;
+import org.springframework.integration.channel.QueueChannel;
+import org.springframework.integration.config.EnableIntegration;
+import org.springframework.integration.dsl.IntegrationFlow;
+import org.springframework.integration.transformer.proto.TestClass1;
+import org.springframework.integration.transformer.proto.TestClass2;
+import org.springframework.integration.transformer.support.ProtoHeaders;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.PollableChannel;
+import org.springframework.messaging.support.GenericMessage;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ *
+ * @author Christian Tzolov
+ *
+ * @since 6.1
+ */
+@SpringJUnitConfig
+public class ProtoTests {
+
+	@Test
+	void testTransformers(@Autowired ProtoConfig config) {
+		TestClass1 test = TestClass1.newBuilder()
+				.setBar("foo")
+				.setQux(678)
+				.build();
+
+		config.in1().send(new GenericMessage<>(test));
+		assertThat(config.tapped().receive(0))
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isInstanceOf(byte[].class);
+		Message<?> received = config.out().receive(0);
+		assertThat(received)
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isEqualTo(test)
+				.isNotSameAs(test);
+		assertThat(received.getHeaders().get("flow")).isEqualTo("flow1");
+	}
+
+	@Test
+	void testTransformersJson(@Autowired ProtoConfig config) {
+		TestClass1 test = TestClass1.newBuilder()
+				.setBar("foo")
+				.setQux(678)
+				.build();
+
+		config.in1().send(new GenericMessage<>(test,
+				Collections.singletonMap(MessageHeaders.CONTENT_TYPE, "application/json")));
+		assertThat(config.tapped().receive(0))
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isInstanceOf(String.class)
+				.isEqualTo("{\n  \"bar\": \"foo\",\n  \"qux\": 678\n}");
+		Message<?> received = config.out().receive(0);
+		assertThat(received)
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isEqualTo(test)
+				.isNotSameAs(test);
+		assertThat(received.getHeaders().get("flow")).isEqualTo("flow1");
+	}
+
+	@Test
+	void testMultiTypeTransformers(@Autowired ProtoConfig config) {
+		TestClass1 test = TestClass1.newBuilder()
+				.setBar("foo")
+				.setQux(678)
+				.build();
+		config.in2().send(new GenericMessage<>(test));
+		assertThat(config.tapped().receive(0))
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isInstanceOf(byte[].class);
+		Message<?> received = config.out().receive(0);
+		assertThat(received)
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isNotEqualTo(test)
+				.isInstanceOf(TestClass2.class);
+		assertThat(received.getHeaders().get("flow")).isEqualTo("flow2");
+	}
+
+	@Test
+	void testMultiTypeTransformersClassName(@Autowired ProtoConfig config) {
+		TestClass1 test = TestClass1.newBuilder()
+				.setBar("foo")
+				.setQux(678)
+				.build();
+		config.in3().send(new GenericMessage<>(test));
+		assertThat(config.tapped().receive(0))
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isInstanceOf(byte[].class);
+		Message<?> received = config.out().receive(0);
+		assertThat(received)
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isNotEqualTo(test)
+				.isInstanceOf(TestClass2.class);
+		assertThat(received.getHeaders().get("flow")).isEqualTo("flow3");
+	}
+
+	@Test
+	void testTransformersNoHeaderPresent(@Autowired ProtoConfig config) {
+		TestClass1 test = TestClass1.newBuilder()
+				.setBar("foo")
+				.setQux(678)
+				.build();
+		config.in4().send(new GenericMessage<>(test));
+		assertThat(config.tapped().receive(0))
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isInstanceOf(byte[].class);
+		Message<?> received = config.out().receive(0);
+		assertThat(received)
+				.isNotNull()
+				.extracting(Message::getPayload)
+				.isEqualTo(test)
+				.isNotSameAs(test);
+		assertThat(received.getHeaders().get("flow")).isEqualTo("flow4");
+	}
+
+	@Configuration
+	@EnableIntegration
+	public static class ProtoConfig {
+
+		@Bean
+		public IntegrationFlow flow1() {
+			return IntegrationFlow.from(in1())
+					.transform(new ToProtobufTransformer())
+					.wireTap(tapped())
+					.transform(new FromProtobufTransformer())
+					.enrichHeaders(h -> h.header("flow", "flow1"))
+					.channel(out())
+					.get();
+		}
+
+		@Bean
+		public IntegrationFlow flow2() {
+			return IntegrationFlow.from(in2())
+					.transform(new ToProtobufTransformer())
+					.wireTap(tapped())
+					.enrichHeaders(h -> h.header(ProtoHeaders.TYPE, TestClass2.class, true))
+					.transform(new FromProtobufTransformer())
+					.enrichHeaders(h -> h.header("flow", "flow2"))
+					.channel(out())
+					.get();
+		}
+
+		@Bean
+		public IntegrationFlow flow3() {
+			return IntegrationFlow.from(in3())
+					.transform(new ToProtobufTransformer())
+					.wireTap(tapped())
+					.enrichHeaders(h -> h.header(ProtoHeaders.TYPE, TestClass2.class.getName(),
+							true))
+					.transform(new FromProtobufTransformer())
+					.enrichHeaders(h -> h.header("flow", "flow3"))
+					.channel(out())
+					.get();
+		}
+
+		@Bean
+		public IntegrationFlow flow4() {
+			return IntegrationFlow.from(in4())
+					.transform(new ToProtobufTransformer())
+					.wireTap(tapped())
+					.enrichHeaders(h -> h.header(ProtoHeaders.TYPE, null, true)
+							.shouldSkipNulls(false))
+					.transform(new FromProtobufTransformer()
+							.setExpectedType(TestClass1.class))
+					.enrichHeaders(h -> h.header("flow", "flow4"))
+					.channel(out())
+					.get();
+		}
+
+		@Bean
+		public DirectChannel in1() {
+			return new DirectChannel();
+		}
+
+		@Bean
+		public DirectChannel in2() {
+			return new DirectChannel();
+		}
+
+		@Bean
+		public DirectChannel in3() {
+			return new DirectChannel();
+		}
+
+		@Bean
+		public DirectChannel in4() {
+			return new DirectChannel();
+		}
+
+		@Bean
+		public PollableChannel tapped() {
+			return new QueueChannel();
+		}
+
+		@Bean
+		public PollableChannel out() {
+			return new QueueChannel();
+		}
+
+	}
+
+}

spring-integration-core/src/test/java/org/springframework/integration/transformer/proto/TestClass1.java

@@ -0,0 +1,671 @@
+// Generated by the protocol buffer compiler.  DO NOT EDIT!
+// source: ProtoTest.proto
+
+package org.springframework.integration.transformer.proto;
+
+/**
+ * Protobuf type {@code tutorial.TestClass1}
+ */
+public  final class TestClass1 extends
+		com.google.protobuf.GeneratedMessageV3 implements
+		// @@protoc_insertion_point(message_implements:tutorial.TestClass1)
+		TestClass1OrBuilder {
+private static final long serialVersionUID = 0L;
+	// Use TestClass1.newBuilder() to construct.
+	private TestClass1(com.google.protobuf.GeneratedMessageV3.Builder<?> builder) {
+		super(builder);
+	}
+	private TestClass1() {
+		bar_ = "";
+	}
+
+	@java.lang.Override
+	@SuppressWarnings({"unused"})
+	protected java.lang.Object newInstance(
+			UnusedPrivateParameter unused) {
+		return new TestClass1();
+	}
+
+	@java.lang.Override
+	public final com.google.protobuf.UnknownFieldSet
+	getUnknownFields() {
+		return this.unknownFields;
+	}
+	private TestClass1(
+			com.google.protobuf.CodedInputStream input,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		this();
+		if (extensionRegistry == null) {
+			throw new java.lang.NullPointerException();
+		}
+		int mutable_bitField0_ = 0;
+		com.google.protobuf.UnknownFieldSet.Builder unknownFields =
+				com.google.protobuf.UnknownFieldSet.newBuilder();
+		try {
+			boolean done = false;
+			while (!done) {
+				int tag = input.readTag();
+				switch (tag) {
+					case 0:
+						done = true;
+						break;
+					case 10: {
+						com.google.protobuf.ByteString bs = input.readBytes();
+						bitField0_ |= 0x00000001;
+						bar_ = bs;
+						break;
+					}
+					case 16: {
+						bitField0_ |= 0x00000002;
+						qux_ = input.readInt32();
+						break;
+					}
+					default: {
+						if (!parseUnknownField(
+								input, unknownFields, extensionRegistry, tag)) {
+							done = true;
+						}
+						break;
+					}
+				}
+			}
+		} catch (com.google.protobuf.InvalidProtocolBufferException e) {
+			throw e.setUnfinishedMessage(this);
+		} catch (java.io.IOException e) {
+			throw new com.google.protobuf.InvalidProtocolBufferException(
+					e).setUnfinishedMessage(this);
+		} finally {
+			this.unknownFields = unknownFields.build();
+			makeExtensionsImmutable();
+		}
+	}
+	public static final com.google.protobuf.Descriptors.Descriptor
+			getDescriptor() {
+		return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass1_descriptor;
+	}
+
+	@java.lang.Override
+	protected com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
+			internalGetFieldAccessorTable() {
+		return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass1_fieldAccessorTable
+				.ensureFieldAccessorsInitialized(
+						org.springframework.integration.transformer.proto.TestClass1.class, org.springframework.integration.transformer.proto.TestClass1.Builder.class);
+	}
+
+	private int bitField0_;
+	public static final int BAR_FIELD_NUMBER = 1;
+	private volatile java.lang.Object bar_;
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return Whether the bar field is set.
+	 */
+	public boolean hasBar() {
+		return ((bitField0_ & 0x00000001) != 0);
+	}
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return The bar.
+	 */
+	public java.lang.String getBar() {
+		java.lang.Object ref = bar_;
+		if (ref instanceof java.lang.String) {
+			return (java.lang.String) ref;
+		} else {
+			com.google.protobuf.ByteString bs =
+					(com.google.protobuf.ByteString) ref;
+			java.lang.String s = bs.toStringUtf8();
+			if (bs.isValidUtf8()) {
+				bar_ = s;
+			}
+			return s;
+		}
+	}
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return The bytes for bar.
+	 */
+	public com.google.protobuf.ByteString
+			getBarBytes() {
+		java.lang.Object ref = bar_;
+		if (ref instanceof java.lang.String) {
+			com.google.protobuf.ByteString b =
+					com.google.protobuf.ByteString.copyFromUtf8(
+							(java.lang.String) ref);
+			bar_ = b;
+			return b;
+		} else {
+			return (com.google.protobuf.ByteString) ref;
+		}
+	}
+
+	public static final int QUX_FIELD_NUMBER = 2;
+	private int qux_;
+	/**
+	 * <code>optional int32 qux = 2;</code>
+	 * @return Whether the qux field is set.
+	 */
+	public boolean hasQux() {
+		return ((bitField0_ & 0x00000002) != 0);
+	}
+	/**
+	 * <code>optional int32 qux = 2;</code>
+	 * @return The qux.
+	 */
+	public int getQux() {
+		return qux_;
+	}
+
+	private byte memoizedIsInitialized = -1;
+	@java.lang.Override
+	public final boolean isInitialized() {
+		byte isInitialized = memoizedIsInitialized;
+		if (isInitialized == 1) return true;
+		if (isInitialized == 0) return false;
+
+		memoizedIsInitialized = 1;
+		return true;
+	}
+
+	@java.lang.Override
+	public void writeTo(com.google.protobuf.CodedOutputStream output)
+											throws java.io.IOException {
+		if (((bitField0_ & 0x00000001) != 0)) {
+			com.google.protobuf.GeneratedMessageV3.writeString(output, 1, bar_);
+		}
+		if (((bitField0_ & 0x00000002) != 0)) {
+			output.writeInt32(2, qux_);
+		}
+		unknownFields.writeTo(output);
+	}
+
+	@java.lang.Override
+	public int getSerializedSize() {
+		int size = memoizedSize;
+		if (size != -1) return size;
+
+		size = 0;
+		if (((bitField0_ & 0x00000001) != 0)) {
+			size += com.google.protobuf.GeneratedMessageV3.computeStringSize(1, bar_);
+		}
+		if (((bitField0_ & 0x00000002) != 0)) {
+			size += com.google.protobuf.CodedOutputStream
+				.computeInt32Size(2, qux_);
+		}
+		size += unknownFields.getSerializedSize();
+		memoizedSize = size;
+		return size;
+	}
+
+	@java.lang.Override
+	public boolean equals(final java.lang.Object obj) {
+		if (obj == this) {
+		 return true;
+		}
+		if (!(obj instanceof org.springframework.integration.transformer.proto.TestClass1)) {
+			return super.equals(obj);
+		}
+		org.springframework.integration.transformer.proto.TestClass1 other = (org.springframework.integration.transformer.proto.TestClass1) obj;
+
+		if (hasBar() != other.hasBar()) return false;
+		if (hasBar()) {
+			if (!getBar()
+					.equals(other.getBar())) return false;
+		}
+		if (hasQux() != other.hasQux()) return false;
+		if (hasQux()) {
+			if (getQux()
+					!= other.getQux()) return false;
+		}
+		if (!unknownFields.equals(other.unknownFields)) return false;
+		return true;
+	}
+
+	@java.lang.Override
+	public int hashCode() {
+		if (memoizedHashCode != 0) {
+			return memoizedHashCode;
+		}
+		int hash = 41;
+		hash = (19 * hash) + getDescriptor().hashCode();
+		if (hasBar()) {
+			hash = (37 * hash) + BAR_FIELD_NUMBER;
+			hash = (53 * hash) + getBar().hashCode();
+		}
+		if (hasQux()) {
+			hash = (37 * hash) + QUX_FIELD_NUMBER;
+			hash = (53 * hash) + getQux();
+		}
+		hash = (29 * hash) + unknownFields.hashCode();
+		memoizedHashCode = hash;
+		return hash;
+	}
+
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(
+			java.nio.ByteBuffer data)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(
+			java.nio.ByteBuffer data,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(
+			com.google.protobuf.ByteString data)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(
+			com.google.protobuf.ByteString data,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(byte[] data)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(
+			byte[] data,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(java.io.InputStream input)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseWithIOException(PARSER, input);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(
+			java.io.InputStream input,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseWithIOException(PARSER, input, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseDelimitedFrom(java.io.InputStream input)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseDelimitedWithIOException(PARSER, input);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseDelimitedFrom(
+			java.io.InputStream input,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseDelimitedWithIOException(PARSER, input, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(
+			com.google.protobuf.CodedInputStream input)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseWithIOException(PARSER, input);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass1 parseFrom(
+			com.google.protobuf.CodedInputStream input,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseWithIOException(PARSER, input, extensionRegistry);
+	}
+
+	@java.lang.Override
+	public Builder newBuilderForType() { return newBuilder(); }
+	public static Builder newBuilder() {
+		return DEFAULT_INSTANCE.toBuilder();
+	}
+	public static Builder newBuilder(org.springframework.integration.transformer.proto.TestClass1 prototype) {
+		return DEFAULT_INSTANCE.toBuilder().mergeFrom(prototype);
+	}
+	@java.lang.Override
+	public Builder toBuilder() {
+		return this == DEFAULT_INSTANCE
+				? new Builder() : new Builder().mergeFrom(this);
+	}
+
+	@java.lang.Override
+	protected Builder newBuilderForType(
+			com.google.protobuf.GeneratedMessageV3.BuilderParent parent) {
+		Builder builder = new Builder(parent);
+		return builder;
+	}
+	/**
+	 * Protobuf type {@code tutorial.TestClass1}
+	 */
+	public static final class Builder extends
+			com.google.protobuf.GeneratedMessageV3.Builder<Builder> implements
+			// @@protoc_insertion_point(builder_implements:tutorial.TestClass1)
+			org.springframework.integration.transformer.proto.TestClass1OrBuilder {
+		public static final com.google.protobuf.Descriptors.Descriptor
+				getDescriptor() {
+			return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass1_descriptor;
+		}
+
+		@java.lang.Override
+		protected com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
+				internalGetFieldAccessorTable() {
+			return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass1_fieldAccessorTable
+					.ensureFieldAccessorsInitialized(
+							org.springframework.integration.transformer.proto.TestClass1.class, org.springframework.integration.transformer.proto.TestClass1.Builder.class);
+		}
+
+		// Construct using org.springframework.integration.transformer.proto.TestClass1.newBuilder()
+		private Builder() {
+			maybeForceBuilderInitialization();
+		}
+
+		private Builder(
+				com.google.protobuf.GeneratedMessageV3.BuilderParent parent) {
+			super(parent);
+			maybeForceBuilderInitialization();
+		}
+		private void maybeForceBuilderInitialization() {
+			if (com.google.protobuf.GeneratedMessageV3
+							.alwaysUseFieldBuilders) {
+			}
+		}
+		@java.lang.Override
+		public Builder clear() {
+			super.clear();
+			bar_ = "";
+			bitField0_ = (bitField0_ & ~0x00000001);
+			qux_ = 0;
+			bitField0_ = (bitField0_ & ~0x00000002);
+			return this;
+		}
+
+		@java.lang.Override
+		public com.google.protobuf.Descriptors.Descriptor
+				getDescriptorForType() {
+			return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass1_descriptor;
+		}
+
+		@java.lang.Override
+		public org.springframework.integration.transformer.proto.TestClass1 getDefaultInstanceForType() {
+			return org.springframework.integration.transformer.proto.TestClass1.getDefaultInstance();
+		}
+
+		@java.lang.Override
+		public org.springframework.integration.transformer.proto.TestClass1 build() {
+			org.springframework.integration.transformer.proto.TestClass1 result = buildPartial();
+			if (!result.isInitialized()) {
+				throw newUninitializedMessageException(result);
+			}
+			return result;
+		}
+
+		@java.lang.Override
+		public org.springframework.integration.transformer.proto.TestClass1 buildPartial() {
+			org.springframework.integration.transformer.proto.TestClass1 result = new org.springframework.integration.transformer.proto.TestClass1(this);
+			int from_bitField0_ = bitField0_;
+			int to_bitField0_ = 0;
+			if (((from_bitField0_ & 0x00000001) != 0)) {
+				to_bitField0_ |= 0x00000001;
+			}
+			result.bar_ = bar_;
+			if (((from_bitField0_ & 0x00000002) != 0)) {
+				result.qux_ = qux_;
+				to_bitField0_ |= 0x00000002;
+			}
+			result.bitField0_ = to_bitField0_;
+			onBuilt();
+			return result;
+		}
+
+		@java.lang.Override
+		public Builder clone() {
+			return super.clone();
+		}
+		@java.lang.Override
+		public Builder setField(
+				com.google.protobuf.Descriptors.FieldDescriptor field,
+				java.lang.Object value) {
+			return super.setField(field, value);
+		}
+		@java.lang.Override
+		public Builder clearField(
+				com.google.protobuf.Descriptors.FieldDescriptor field) {
+			return super.clearField(field);
+		}
+		@java.lang.Override
+		public Builder clearOneof(
+				com.google.protobuf.Descriptors.OneofDescriptor oneof) {
+			return super.clearOneof(oneof);
+		}
+		@java.lang.Override
+		public Builder setRepeatedField(
+				com.google.protobuf.Descriptors.FieldDescriptor field,
+				int index, java.lang.Object value) {
+			return super.setRepeatedField(field, index, value);
+		}
+		@java.lang.Override
+		public Builder addRepeatedField(
+				com.google.protobuf.Descriptors.FieldDescriptor field,
+				java.lang.Object value) {
+			return super.addRepeatedField(field, value);
+		}
+		@java.lang.Override
+		public Builder mergeFrom(com.google.protobuf.Message other) {
+			if (other instanceof org.springframework.integration.transformer.proto.TestClass1) {
+				return mergeFrom((org.springframework.integration.transformer.proto.TestClass1)other);
+			} else {
+				super.mergeFrom(other);
+				return this;
+			}
+		}
+
+		public Builder mergeFrom(org.springframework.integration.transformer.proto.TestClass1 other) {
+			if (other == org.springframework.integration.transformer.proto.TestClass1.getDefaultInstance()) return this;
+			if (other.hasBar()) {
+				bitField0_ |= 0x00000001;
+				bar_ = other.bar_;
+				onChanged();
+			}
+			if (other.hasQux()) {
+				setQux(other.getQux());
+			}
+			this.mergeUnknownFields(other.unknownFields);
+			onChanged();
+			return this;
+		}
+
+		@java.lang.Override
+		public final boolean isInitialized() {
+			return true;
+		}
+
+		@java.lang.Override
+		public Builder mergeFrom(
+				com.google.protobuf.CodedInputStream input,
+				com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+				throws java.io.IOException {
+			org.springframework.integration.transformer.proto.TestClass1 parsedMessage = null;
+			try {
+				parsedMessage = PARSER.parsePartialFrom(input, extensionRegistry);
+			} catch (com.google.protobuf.InvalidProtocolBufferException e) {
+				parsedMessage = (org.springframework.integration.transformer.proto.TestClass1) e.getUnfinishedMessage();
+				throw e.unwrapIOException();
+			} finally {
+				if (parsedMessage != null) {
+					mergeFrom(parsedMessage);
+				}
+			}
+			return this;
+		}
+		private int bitField0_;
+
+		private java.lang.Object bar_ = "";
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @return Whether the bar field is set.
+		 */
+		public boolean hasBar() {
+			return ((bitField0_ & 0x00000001) != 0);
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @return The bar.
+		 */
+		public java.lang.String getBar() {
+			java.lang.Object ref = bar_;
+			if (!(ref instanceof java.lang.String)) {
+				com.google.protobuf.ByteString bs =
+						(com.google.protobuf.ByteString) ref;
+				java.lang.String s = bs.toStringUtf8();
+				if (bs.isValidUtf8()) {
+					bar_ = s;
+				}
+				return s;
+			} else {
+				return (java.lang.String) ref;
+			}
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @return The bytes for bar.
+		 */
+		public com.google.protobuf.ByteString
+				getBarBytes() {
+			java.lang.Object ref = bar_;
+			if (ref instanceof String) {
+				com.google.protobuf.ByteString b =
+						com.google.protobuf.ByteString.copyFromUtf8(
+								(java.lang.String) ref);
+				bar_ = b;
+				return b;
+			} else {
+				return (com.google.protobuf.ByteString) ref;
+			}
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @param value The bar to set.
+		 * @return This builder for chaining.
+		 */
+		public Builder setBar(
+				java.lang.String value) {
+			if (value == null) {
+		throw new NullPointerException();
+	}
+	bitField0_ |= 0x00000001;
+			bar_ = value;
+			onChanged();
+			return this;
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @return This builder for chaining.
+		 */
+		public Builder clearBar() {
+			bitField0_ = (bitField0_ & ~0x00000001);
+			bar_ = getDefaultInstance().getBar();
+			onChanged();
+			return this;
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @param value The bytes for bar to set.
+		 * @return This builder for chaining.
+		 */
+		public Builder setBarBytes(
+				com.google.protobuf.ByteString value) {
+			if (value == null) {
+		throw new NullPointerException();
+	}
+	bitField0_ |= 0x00000001;
+			bar_ = value;
+			onChanged();
+			return this;
+		}
+
+		private int qux_ ;
+		/**
+		 * <code>optional int32 qux = 2;</code>
+		 * @return Whether the qux field is set.
+		 */
+		public boolean hasQux() {
+			return ((bitField0_ & 0x00000002) != 0);
+		}
+		/**
+		 * <code>optional int32 qux = 2;</code>
+		 * @return The qux.
+		 */
+		public int getQux() {
+			return qux_;
+		}
+		/**
+		 * <code>optional int32 qux = 2;</code>
+		 * @param value The qux to set.
+		 * @return This builder for chaining.
+		 */
+		public Builder setQux(int value) {
+			bitField0_ |= 0x00000002;
+			qux_ = value;
+			onChanged();
+			return this;
+		}
+		/**
+		 * <code>optional int32 qux = 2;</code>
+		 * @return This builder for chaining.
+		 */
+		public Builder clearQux() {
+			bitField0_ = (bitField0_ & ~0x00000002);
+			qux_ = 0;
+			onChanged();
+			return this;
+		}
+		@java.lang.Override
+		public final Builder setUnknownFields(
+				final com.google.protobuf.UnknownFieldSet unknownFields) {
+			return super.setUnknownFields(unknownFields);
+		}
+
+		@java.lang.Override
+		public final Builder mergeUnknownFields(
+				final com.google.protobuf.UnknownFieldSet unknownFields) {
+			return super.mergeUnknownFields(unknownFields);
+		}
+
+
+		// @@protoc_insertion_point(builder_scope:tutorial.TestClass1)
+	}
+
+	// @@protoc_insertion_point(class_scope:tutorial.TestClass1)
+	private static final org.springframework.integration.transformer.proto.TestClass1 DEFAULT_INSTANCE;
+	static {
+		DEFAULT_INSTANCE = new org.springframework.integration.transformer.proto.TestClass1();
+	}
+
+	public static org.springframework.integration.transformer.proto.TestClass1 getDefaultInstance() {
+		return DEFAULT_INSTANCE;
+	}
+
+	@java.lang.Deprecated public static final com.google.protobuf.Parser<TestClass1>
+			PARSER = new com.google.protobuf.AbstractParser<TestClass1>() {
+		@java.lang.Override
+		public TestClass1 parsePartialFrom(
+				com.google.protobuf.CodedInputStream input,
+				com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+				throws com.google.protobuf.InvalidProtocolBufferException {
+			return new TestClass1(input, extensionRegistry);
+		}
+	};
+
+	public static com.google.protobuf.Parser<TestClass1> parser() {
+		return PARSER;
+	}
+
+	@java.lang.Override
+	public com.google.protobuf.Parser<TestClass1> getParserForType() {
+		return PARSER;
+	}
+
+	@java.lang.Override
+	public org.springframework.integration.transformer.proto.TestClass1 getDefaultInstanceForType() {
+		return DEFAULT_INSTANCE;
+	}
+
+}
+

spring-integration-core/src/test/java/org/springframework/integration/transformer/proto/TestClass1OrBuilder.java

@@ -0,0 +1,37 @@
+// Generated by the protocol buffer compiler.  DO NOT EDIT!
+// source: ProtoTest.proto
+
+package org.springframework.integration.transformer.proto;
+
+public interface TestClass1OrBuilder extends
+		// @@protoc_insertion_point(interface_extends:tutorial.TestClass1)
+		com.google.protobuf.MessageOrBuilder {
+
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return Whether the bar field is set.
+	 */
+	boolean hasBar();
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return The bar.
+	 */
+	java.lang.String getBar();
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return The bytes for bar.
+	 */
+	com.google.protobuf.ByteString
+			getBarBytes();
+
+	/**
+	 * <code>optional int32 qux = 2;</code>
+	 * @return Whether the qux field is set.
+	 */
+	boolean hasQux();
+	/**
+	 * <code>optional int32 qux = 2;</code>
+	 * @return The qux.
+	 */
+	int getQux();
+}

spring-integration-core/src/test/java/org/springframework/integration/transformer/proto/TestClass2.java

@@ -0,0 +1,671 @@
+// Generated by the protocol buffer compiler.  DO NOT EDIT!
+// source: ProtoTest.proto
+
+package org.springframework.integration.transformer.proto;
+
+/**
+ * Protobuf type {@code tutorial.TestClass2}
+ */
+public  final class TestClass2 extends
+		com.google.protobuf.GeneratedMessageV3 implements
+		// @@protoc_insertion_point(message_implements:tutorial.TestClass2)
+		TestClass2OrBuilder {
+private static final long serialVersionUID = 0L;
+	// Use TestClass2.newBuilder() to construct.
+	private TestClass2(com.google.protobuf.GeneratedMessageV3.Builder<?> builder) {
+		super(builder);
+	}
+	private TestClass2() {
+		bar_ = "";
+	}
+
+	@java.lang.Override
+	@SuppressWarnings({"unused"})
+	protected java.lang.Object newInstance(
+			UnusedPrivateParameter unused) {
+		return new TestClass2();
+	}
+
+	@java.lang.Override
+	public final com.google.protobuf.UnknownFieldSet
+	getUnknownFields() {
+		return this.unknownFields;
+	}
+	private TestClass2(
+			com.google.protobuf.CodedInputStream input,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		this();
+		if (extensionRegistry == null) {
+			throw new java.lang.NullPointerException();
+		}
+		int mutable_bitField0_ = 0;
+		com.google.protobuf.UnknownFieldSet.Builder unknownFields =
+				com.google.protobuf.UnknownFieldSet.newBuilder();
+		try {
+			boolean done = false;
+			while (!done) {
+				int tag = input.readTag();
+				switch (tag) {
+					case 0:
+						done = true;
+						break;
+					case 10: {
+						com.google.protobuf.ByteString bs = input.readBytes();
+						bitField0_ |= 0x00000001;
+						bar_ = bs;
+						break;
+					}
+					case 16: {
+						bitField0_ |= 0x00000002;
+						qux_ = input.readInt32();
+						break;
+					}
+					default: {
+						if (!parseUnknownField(
+								input, unknownFields, extensionRegistry, tag)) {
+							done = true;
+						}
+						break;
+					}
+				}
+			}
+		} catch (com.google.protobuf.InvalidProtocolBufferException e) {
+			throw e.setUnfinishedMessage(this);
+		} catch (java.io.IOException e) {
+			throw new com.google.protobuf.InvalidProtocolBufferException(
+					e).setUnfinishedMessage(this);
+		} finally {
+			this.unknownFields = unknownFields.build();
+			makeExtensionsImmutable();
+		}
+	}
+	public static final com.google.protobuf.Descriptors.Descriptor
+			getDescriptor() {
+		return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass2_descriptor;
+	}
+
+	@java.lang.Override
+	protected com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
+			internalGetFieldAccessorTable() {
+		return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass2_fieldAccessorTable
+				.ensureFieldAccessorsInitialized(
+						org.springframework.integration.transformer.proto.TestClass2.class, org.springframework.integration.transformer.proto.TestClass2.Builder.class);
+	}
+
+	private int bitField0_;
+	public static final int BAR_FIELD_NUMBER = 1;
+	private volatile java.lang.Object bar_;
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return Whether the bar field is set.
+	 */
+	public boolean hasBar() {
+		return ((bitField0_ & 0x00000001) != 0);
+	}
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return The bar.
+	 */
+	public java.lang.String getBar() {
+		java.lang.Object ref = bar_;
+		if (ref instanceof java.lang.String) {
+			return (java.lang.String) ref;
+		} else {
+			com.google.protobuf.ByteString bs =
+					(com.google.protobuf.ByteString) ref;
+			java.lang.String s = bs.toStringUtf8();
+			if (bs.isValidUtf8()) {
+				bar_ = s;
+			}
+			return s;
+		}
+	}
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return The bytes for bar.
+	 */
+	public com.google.protobuf.ByteString
+			getBarBytes() {
+		java.lang.Object ref = bar_;
+		if (ref instanceof java.lang.String) {
+			com.google.protobuf.ByteString b =
+					com.google.protobuf.ByteString.copyFromUtf8(
+							(java.lang.String) ref);
+			bar_ = b;
+			return b;
+		} else {
+			return (com.google.protobuf.ByteString) ref;
+		}
+	}
+
+	public static final int QUX_FIELD_NUMBER = 2;
+	private int qux_;
+	/**
+	 * <code>optional int32 qux = 2;</code>
+	 * @return Whether the qux field is set.
+	 */
+	public boolean hasQux() {
+		return ((bitField0_ & 0x00000002) != 0);
+	}
+	/**
+	 * <code>optional int32 qux = 2;</code>
+	 * @return The qux.
+	 */
+	public int getQux() {
+		return qux_;
+	}
+
+	private byte memoizedIsInitialized = -1;
+	@java.lang.Override
+	public final boolean isInitialized() {
+		byte isInitialized = memoizedIsInitialized;
+		if (isInitialized == 1) return true;
+		if (isInitialized == 0) return false;
+
+		memoizedIsInitialized = 1;
+		return true;
+	}
+
+	@java.lang.Override
+	public void writeTo(com.google.protobuf.CodedOutputStream output)
+											throws java.io.IOException {
+		if (((bitField0_ & 0x00000001) != 0)) {
+			com.google.protobuf.GeneratedMessageV3.writeString(output, 1, bar_);
+		}
+		if (((bitField0_ & 0x00000002) != 0)) {
+			output.writeInt32(2, qux_);
+		}
+		unknownFields.writeTo(output);
+	}
+
+	@java.lang.Override
+	public int getSerializedSize() {
+		int size = memoizedSize;
+		if (size != -1) return size;
+
+		size = 0;
+		if (((bitField0_ & 0x00000001) != 0)) {
+			size += com.google.protobuf.GeneratedMessageV3.computeStringSize(1, bar_);
+		}
+		if (((bitField0_ & 0x00000002) != 0)) {
+			size += com.google.protobuf.CodedOutputStream
+				.computeInt32Size(2, qux_);
+		}
+		size += unknownFields.getSerializedSize();
+		memoizedSize = size;
+		return size;
+	}
+
+	@java.lang.Override
+	public boolean equals(final java.lang.Object obj) {
+		if (obj == this) {
+		 return true;
+		}
+		if (!(obj instanceof org.springframework.integration.transformer.proto.TestClass2)) {
+			return super.equals(obj);
+		}
+		org.springframework.integration.transformer.proto.TestClass2 other = (org.springframework.integration.transformer.proto.TestClass2) obj;
+
+		if (hasBar() != other.hasBar()) return false;
+		if (hasBar()) {
+			if (!getBar()
+					.equals(other.getBar())) return false;
+		}
+		if (hasQux() != other.hasQux()) return false;
+		if (hasQux()) {
+			if (getQux()
+					!= other.getQux()) return false;
+		}
+		if (!unknownFields.equals(other.unknownFields)) return false;
+		return true;
+	}
+
+	@java.lang.Override
+	public int hashCode() {
+		if (memoizedHashCode != 0) {
+			return memoizedHashCode;
+		}
+		int hash = 41;
+		hash = (19 * hash) + getDescriptor().hashCode();
+		if (hasBar()) {
+			hash = (37 * hash) + BAR_FIELD_NUMBER;
+			hash = (53 * hash) + getBar().hashCode();
+		}
+		if (hasQux()) {
+			hash = (37 * hash) + QUX_FIELD_NUMBER;
+			hash = (53 * hash) + getQux();
+		}
+		hash = (29 * hash) + unknownFields.hashCode();
+		memoizedHashCode = hash;
+		return hash;
+	}
+
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(
+			java.nio.ByteBuffer data)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(
+			java.nio.ByteBuffer data,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(
+			com.google.protobuf.ByteString data)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(
+			com.google.protobuf.ByteString data,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(byte[] data)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(
+			byte[] data,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws com.google.protobuf.InvalidProtocolBufferException {
+		return PARSER.parseFrom(data, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(java.io.InputStream input)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseWithIOException(PARSER, input);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(
+			java.io.InputStream input,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseWithIOException(PARSER, input, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseDelimitedFrom(java.io.InputStream input)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseDelimitedWithIOException(PARSER, input);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseDelimitedFrom(
+			java.io.InputStream input,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseDelimitedWithIOException(PARSER, input, extensionRegistry);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(
+			com.google.protobuf.CodedInputStream input)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseWithIOException(PARSER, input);
+	}
+	public static org.springframework.integration.transformer.proto.TestClass2 parseFrom(
+			com.google.protobuf.CodedInputStream input,
+			com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+			throws java.io.IOException {
+		return com.google.protobuf.GeneratedMessageV3
+				.parseWithIOException(PARSER, input, extensionRegistry);
+	}
+
+	@java.lang.Override
+	public Builder newBuilderForType() { return newBuilder(); }
+	public static Builder newBuilder() {
+		return DEFAULT_INSTANCE.toBuilder();
+	}
+	public static Builder newBuilder(org.springframework.integration.transformer.proto.TestClass2 prototype) {
+		return DEFAULT_INSTANCE.toBuilder().mergeFrom(prototype);
+	}
+	@java.lang.Override
+	public Builder toBuilder() {
+		return this == DEFAULT_INSTANCE
+				? new Builder() : new Builder().mergeFrom(this);
+	}
+
+	@java.lang.Override
+	protected Builder newBuilderForType(
+			com.google.protobuf.GeneratedMessageV3.BuilderParent parent) {
+		Builder builder = new Builder(parent);
+		return builder;
+	}
+	/**
+	 * Protobuf type {@code tutorial.TestClass2}
+	 */
+	public static final class Builder extends
+			com.google.protobuf.GeneratedMessageV3.Builder<Builder> implements
+			// @@protoc_insertion_point(builder_implements:tutorial.TestClass2)
+			org.springframework.integration.transformer.proto.TestClass2OrBuilder {
+		public static final com.google.protobuf.Descriptors.Descriptor
+				getDescriptor() {
+			return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass2_descriptor;
+		}
+
+		@java.lang.Override
+		protected com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
+				internalGetFieldAccessorTable() {
+			return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass2_fieldAccessorTable
+					.ensureFieldAccessorsInitialized(
+							org.springframework.integration.transformer.proto.TestClass2.class, org.springframework.integration.transformer.proto.TestClass2.Builder.class);
+		}
+
+		// Construct using org.springframework.integration.transformer.proto.TestClass2.newBuilder()
+		private Builder() {
+			maybeForceBuilderInitialization();
+		}
+
+		private Builder(
+				com.google.protobuf.GeneratedMessageV3.BuilderParent parent) {
+			super(parent);
+			maybeForceBuilderInitialization();
+		}
+		private void maybeForceBuilderInitialization() {
+			if (com.google.protobuf.GeneratedMessageV3
+							.alwaysUseFieldBuilders) {
+			}
+		}
+		@java.lang.Override
+		public Builder clear() {
+			super.clear();
+			bar_ = "";
+			bitField0_ = (bitField0_ & ~0x00000001);
+			qux_ = 0;
+			bitField0_ = (bitField0_ & ~0x00000002);
+			return this;
+		}
+
+		@java.lang.Override
+		public com.google.protobuf.Descriptors.Descriptor
+				getDescriptorForType() {
+			return org.springframework.integration.transformer.proto.TestProtos.internal_static_tutorial_TestClass2_descriptor;
+		}
+
+		@java.lang.Override
+		public org.springframework.integration.transformer.proto.TestClass2 getDefaultInstanceForType() {
+			return org.springframework.integration.transformer.proto.TestClass2.getDefaultInstance();
+		}
+
+		@java.lang.Override
+		public org.springframework.integration.transformer.proto.TestClass2 build() {
+			org.springframework.integration.transformer.proto.TestClass2 result = buildPartial();
+			if (!result.isInitialized()) {
+				throw newUninitializedMessageException(result);
+			}
+			return result;
+		}
+
+		@java.lang.Override
+		public org.springframework.integration.transformer.proto.TestClass2 buildPartial() {
+			org.springframework.integration.transformer.proto.TestClass2 result = new org.springframework.integration.transformer.proto.TestClass2(this);
+			int from_bitField0_ = bitField0_;
+			int to_bitField0_ = 0;
+			if (((from_bitField0_ & 0x00000001) != 0)) {
+				to_bitField0_ |= 0x00000001;
+			}
+			result.bar_ = bar_;
+			if (((from_bitField0_ & 0x00000002) != 0)) {
+				result.qux_ = qux_;
+				to_bitField0_ |= 0x00000002;
+			}
+			result.bitField0_ = to_bitField0_;
+			onBuilt();
+			return result;
+		}
+
+		@java.lang.Override
+		public Builder clone() {
+			return super.clone();
+		}
+		@java.lang.Override
+		public Builder setField(
+				com.google.protobuf.Descriptors.FieldDescriptor field,
+				java.lang.Object value) {
+			return super.setField(field, value);
+		}
+		@java.lang.Override
+		public Builder clearField(
+				com.google.protobuf.Descriptors.FieldDescriptor field) {
+			return super.clearField(field);
+		}
+		@java.lang.Override
+		public Builder clearOneof(
+				com.google.protobuf.Descriptors.OneofDescriptor oneof) {
+			return super.clearOneof(oneof);
+		}
+		@java.lang.Override
+		public Builder setRepeatedField(
+				com.google.protobuf.Descriptors.FieldDescriptor field,
+				int index, java.lang.Object value) {
+			return super.setRepeatedField(field, index, value);
+		}
+		@java.lang.Override
+		public Builder addRepeatedField(
+				com.google.protobuf.Descriptors.FieldDescriptor field,
+				java.lang.Object value) {
+			return super.addRepeatedField(field, value);
+		}
+		@java.lang.Override
+		public Builder mergeFrom(com.google.protobuf.Message other) {
+			if (other instanceof org.springframework.integration.transformer.proto.TestClass2) {
+				return mergeFrom((org.springframework.integration.transformer.proto.TestClass2)other);
+			} else {
+				super.mergeFrom(other);
+				return this;
+			}
+		}
+
+		public Builder mergeFrom(org.springframework.integration.transformer.proto.TestClass2 other) {
+			if (other == org.springframework.integration.transformer.proto.TestClass2.getDefaultInstance()) return this;
+			if (other.hasBar()) {
+				bitField0_ |= 0x00000001;
+				bar_ = other.bar_;
+				onChanged();
+			}
+			if (other.hasQux()) {
+				setQux(other.getQux());
+			}
+			this.mergeUnknownFields(other.unknownFields);
+			onChanged();
+			return this;
+		}
+
+		@java.lang.Override
+		public final boolean isInitialized() {
+			return true;
+		}
+
+		@java.lang.Override
+		public Builder mergeFrom(
+				com.google.protobuf.CodedInputStream input,
+				com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+				throws java.io.IOException {
+			org.springframework.integration.transformer.proto.TestClass2 parsedMessage = null;
+			try {
+				parsedMessage = PARSER.parsePartialFrom(input, extensionRegistry);
+			} catch (com.google.protobuf.InvalidProtocolBufferException e) {
+				parsedMessage = (org.springframework.integration.transformer.proto.TestClass2) e.getUnfinishedMessage();
+				throw e.unwrapIOException();
+			} finally {
+				if (parsedMessage != null) {
+					mergeFrom(parsedMessage);
+				}
+			}
+			return this;
+		}
+		private int bitField0_;
+
+		private java.lang.Object bar_ = "";
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @return Whether the bar field is set.
+		 */
+		public boolean hasBar() {
+			return ((bitField0_ & 0x00000001) != 0);
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @return The bar.
+		 */
+		public java.lang.String getBar() {
+			java.lang.Object ref = bar_;
+			if (!(ref instanceof java.lang.String)) {
+				com.google.protobuf.ByteString bs =
+						(com.google.protobuf.ByteString) ref;
+				java.lang.String s = bs.toStringUtf8();
+				if (bs.isValidUtf8()) {
+					bar_ = s;
+				}
+				return s;
+			} else {
+				return (java.lang.String) ref;
+			}
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @return The bytes for bar.
+		 */
+		public com.google.protobuf.ByteString
+				getBarBytes() {
+			java.lang.Object ref = bar_;
+			if (ref instanceof String) {
+				com.google.protobuf.ByteString b =
+						com.google.protobuf.ByteString.copyFromUtf8(
+								(java.lang.String) ref);
+				bar_ = b;
+				return b;
+			} else {
+				return (com.google.protobuf.ByteString) ref;
+			}
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @param value The bar to set.
+		 * @return This builder for chaining.
+		 */
+		public Builder setBar(
+				java.lang.String value) {
+			if (value == null) {
+		throw new NullPointerException();
+	}
+	bitField0_ |= 0x00000001;
+			bar_ = value;
+			onChanged();
+			return this;
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @return This builder for chaining.
+		 */
+		public Builder clearBar() {
+			bitField0_ = (bitField0_ & ~0x00000001);
+			bar_ = getDefaultInstance().getBar();
+			onChanged();
+			return this;
+		}
+		/**
+		 * <code>optional string bar = 1;</code>
+		 * @param value The bytes for bar to set.
+		 * @return This builder for chaining.
+		 */
+		public Builder setBarBytes(
+				com.google.protobuf.ByteString value) {
+			if (value == null) {
+		throw new NullPointerException();
+	}
+	bitField0_ |= 0x00000001;
+			bar_ = value;
+			onChanged();
+			return this;
+		}
+
+		private int qux_ ;
+		/**
+		 * <code>optional int32 qux = 2;</code>
+		 * @return Whether the qux field is set.
+		 */
+		public boolean hasQux() {
+			return ((bitField0_ & 0x00000002) != 0);
+		}
+		/**
+		 * <code>optional int32 qux = 2;</code>
+		 * @return The qux.
+		 */
+		public int getQux() {
+			return qux_;
+		}
+		/**
+		 * <code>optional int32 qux = 2;</code>
+		 * @param value The qux to set.
+		 * @return This builder for chaining.
+		 */
+		public Builder setQux(int value) {
+			bitField0_ |= 0x00000002;
+			qux_ = value;
+			onChanged();
+			return this;
+		}
+		/**
+		 * <code>optional int32 qux = 2;</code>
+		 * @return This builder for chaining.
+		 */
+		public Builder clearQux() {
+			bitField0_ = (bitField0_ & ~0x00000002);
+			qux_ = 0;
+			onChanged();
+			return this;
+		}
+		@java.lang.Override
+		public final Builder setUnknownFields(
+				final com.google.protobuf.UnknownFieldSet unknownFields) {
+			return super.setUnknownFields(unknownFields);
+		}
+
+		@java.lang.Override
+		public final Builder mergeUnknownFields(
+				final com.google.protobuf.UnknownFieldSet unknownFields) {
+			return super.mergeUnknownFields(unknownFields);
+		}
+
+
+		// @@protoc_insertion_point(builder_scope:tutorial.TestClass2)
+	}
+
+	// @@protoc_insertion_point(class_scope:tutorial.TestClass2)
+	private static final org.springframework.integration.transformer.proto.TestClass2 DEFAULT_INSTANCE;
+	static {
+		DEFAULT_INSTANCE = new org.springframework.integration.transformer.proto.TestClass2();
+	}
+
+	public static org.springframework.integration.transformer.proto.TestClass2 getDefaultInstance() {
+		return DEFAULT_INSTANCE;
+	}
+
+	@java.lang.Deprecated public static final com.google.protobuf.Parser<TestClass2>
+			PARSER = new com.google.protobuf.AbstractParser<TestClass2>() {
+		@java.lang.Override
+		public TestClass2 parsePartialFrom(
+				com.google.protobuf.CodedInputStream input,
+				com.google.protobuf.ExtensionRegistryLite extensionRegistry)
+				throws com.google.protobuf.InvalidProtocolBufferException {
+			return new TestClass2(input, extensionRegistry);
+		}
+	};
+
+	public static com.google.protobuf.Parser<TestClass2> parser() {
+		return PARSER;
+	}
+
+	@java.lang.Override
+	public com.google.protobuf.Parser<TestClass2> getParserForType() {
+		return PARSER;
+	}
+
+	@java.lang.Override
+	public org.springframework.integration.transformer.proto.TestClass2 getDefaultInstanceForType() {
+		return DEFAULT_INSTANCE;
+	}
+
+}
+

spring-integration-core/src/test/java/org/springframework/integration/transformer/proto/TestClass2OrBuilder.java

@@ -0,0 +1,37 @@
+// Generated by the protocol buffer compiler.  DO NOT EDIT!
+// source: ProtoTest.proto
+
+package org.springframework.integration.transformer.proto;
+
+public interface TestClass2OrBuilder extends
+		// @@protoc_insertion_point(interface_extends:tutorial.TestClass2)
+		com.google.protobuf.MessageOrBuilder {
+
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return Whether the bar field is set.
+	 */
+	boolean hasBar();
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return The bar.
+	 */
+	java.lang.String getBar();
+	/**
+	 * <code>optional string bar = 1;</code>
+	 * @return The bytes for bar.
+	 */
+	com.google.protobuf.ByteString
+			getBarBytes();
+
+	/**
+	 * <code>optional int32 qux = 2;</code>
+	 * @return Whether the qux field is set.
+	 */
+	boolean hasQux();
+	/**
+	 * <code>optional int32 qux = 2;</code>
+	 * @return The qux.
+	 */
+	int getQux();
+}

spring-integration-core/src/test/java/org/springframework/integration/transformer/proto/TestProtos.java

@@ -0,0 +1,61 @@
+// Generated by the protocol buffer compiler.  DO NOT EDIT!
+// source: ProtoTest.proto
+
+package org.springframework.integration.transformer.proto;
+
+public final class TestProtos {
+	private TestProtos() {}
+	public static void registerAllExtensions(
+			com.google.protobuf.ExtensionRegistryLite registry) {
+	}
+
+	public static void registerAllExtensions(
+			com.google.protobuf.ExtensionRegistry registry) {
+		registerAllExtensions(
+				(com.google.protobuf.ExtensionRegistryLite) registry);
+	}
+	static final com.google.protobuf.Descriptors.Descriptor
+		internal_static_tutorial_TestClass1_descriptor;
+	static final
+		com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
+			internal_static_tutorial_TestClass1_fieldAccessorTable;
+	static final com.google.protobuf.Descriptors.Descriptor
+		internal_static_tutorial_TestClass2_descriptor;
+	static final
+		com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
+			internal_static_tutorial_TestClass2_fieldAccessorTable;
+
+	public static com.google.protobuf.Descriptors.FileDescriptor
+			getDescriptor() {
+		return descriptor;
+	}
+	private static  com.google.protobuf.Descriptors.FileDescriptor
+			descriptor;
+	static {
+		java.lang.String[] descriptorData = {
+			"\n\017ProtoTest.proto\022\010tutorial\"&\n\nTestClass" +
+			"1\022\013\n\003bar\030\001 \001(\t\022\013\n\003qux\030\002 \001(\005\"&\n\nTestClass" +
+			"2\022\013\n\003bar\030\001 \001(\t\022\013\n\003qux\030\002 \001(\005BA\n1org.sprin" +
+			"gframework.integration.transformer.proto" +
+			"B\nTestProtosP\001"
+		};
+		descriptor = com.google.protobuf.Descriptors.FileDescriptor
+			.internalBuildGeneratedFileFrom(descriptorData,
+				new com.google.protobuf.Descriptors.FileDescriptor[] {
+				});
+		internal_static_tutorial_TestClass1_descriptor =
+			getDescriptor().getMessageTypes().get(0);
+		internal_static_tutorial_TestClass1_fieldAccessorTable = new
+			com.google.protobuf.GeneratedMessageV3.FieldAccessorTable(
+				internal_static_tutorial_TestClass1_descriptor,
+				new java.lang.String[] { "Bar", "Qux", });
+		internal_static_tutorial_TestClass2_descriptor =
+			getDescriptor().getMessageTypes().get(1);
+		internal_static_tutorial_TestClass2_fieldAccessorTable = new
+			com.google.protobuf.GeneratedMessageV3.FieldAccessorTable(
+				internal_static_tutorial_TestClass2_descriptor,
+				new java.lang.String[] { "Bar", "Qux", });
+	}
+
+	// @@protoc_insertion_point(outer_class_scope)
+}

spring-integration-core/src/test/resources/proto/ProtoTest.proto

@@ -0,0 +1,17 @@
+syntax = "proto2";
+
+package tutorial;
+
+option java_multiple_files = true;
+option java_package = "org.springframework.integration.transformer.proto";
+option java_outer_classname = "TestProtos";
+
+message TestClass1 {
+  optional string bar = 1;
+  optional int32 qux = 2;
+}
+
+message TestClass2 {
+  optional string bar = 1;
+  optional int32 qux = 2;
+}

src/checkstyle/checkstyle-suppressions.xml

@@ -13,4 +13,5 @@
 	<suppress files="[\\/]test[\\/]" checks="EqualsHashCode"/>
 	<suppress files="[\\/]test[\\/]" checks="Atclause*"/>
 	<suppress files="[\\/]test[\\/]" checks="InterfaceIsType"/>
+	<suppress files="org[\\/]springframework[\\/]integration[\\/]transformer[\\/]proto" checks=".*"/>
 </suppressions>

src/reference/asciidoc/transformer.adoc

@@ -249,8 +249,8 @@ Spring Integration provides namespace support for Map-to-Object, as the followin
 ====
 [source,xml]
 ----
-<int:map-to-object-transformer input-channel="input" 
-                         output-channel="output" 
+<int:map-to-object-transformer input-channel="input"
+                         output-channel="output"
                          type="org.something.Person"/>
 ----
 ====
@@ -258,7 +258,7 @@ Spring Integration provides namespace support for Map-to-Object, as the followin
 Alternatively, you could use a `ref` attribute and a prototype-scoped bean, as the following example shows:
 [source,xml]
 ----
-<int:map-to-object-transformer input-channel="inputA" 
+<int:map-to-object-transformer input-channel="inputA"
                                output-channel="outputA"
                                ref="person"/>
 <bean id="person" class="org.something.Person" scope="prototype"/>
@@ -267,7 +267,7 @@ Alternatively, you could use a `ref` attribute and a prototype-scoped bean, as t
 
 NOTE: The 'ref' and 'type' attributes are mutually exclusive.
 Also, if you use the 'ref' attribute, you must point to a 'prototype' scoped bean.
-Otherwise, a `BeanCreationException` is thrown. 
+Otherwise, a `BeanCreationException` is thrown.
 
 Starting with version 5.0, you can supply the `ObjectToMapTransformer` with a customized `JsonObjectMapper` -- for when you need special formats for dates or nulls for empty collections (and other uses).
 See <<json-transformers>> for more information about `JsonObjectMapper` implementations.
@@ -446,6 +446,64 @@ If the expression returns `null`, the `defaultType` is used.
 The `SimpleToAvroTransformer` also has a `setTypeExpression` method.
 This allows decoupling of the producer and consumer where the sender can set the header to some token representing the type and the consumer then maps that token to a type.
 
+[[Protobuf-transformers]]
+===== Protocol Buffers Transformers
+
+Version 6.1 adds support for transforming from and to https://protobuf.dev/[Protocol Buffers] data content.
+
+The `ToProtobufTransformer` transforms a `com.google.protobuf.Message` message payloads into native byte array or json text payloads.
+The `application/x-protobuf` content type (used by default) produces byte array output payload.
+If the content type is `application/json` add the `com.google.protobuf:protobuf-java-util` if found on the classpath, then the output is text json payload.
+If the content type header is not set the `ToProtobufTransformer` defaults to `application/x-protobuf`.
+
+The `FromProtobufTransformer` transforms byte array or text protobuf payload (depending on the content type) back into `com.google.protobuf.Message` instances.
+The `FromProtobufTransformer` should specify either an expected class type explicitly (use the `setExpectedType` method) or use a SpEL expression to determine the type to deserialize using the `setExpectedTypeExpression` method.
+The default SpEL expression is `headers[proto_type]` (`ProtoHeaders.TYPE`) which is populated by the `ToProtobufTransformer` with the fully qualified class name of the source `com.google.protobuf.Message` class.
+
+For example, compiling the following IDL:
+
+====
+[source,proto]
+----
+syntax = "proto2";
+package tutorial;
+
+option java_multiple_files = true;
+option java_package = "org.example";
+option java_outer_classname = "MyProtos";
+
+message MyMessageClass {
+  optional string foo = 1;
+  optional string bar = 2;
+}
+----
+====
+
+will generate a new `org.example.MyMessageClass` class.
+
+Then use the:
+====
+[source,java]
+----
+// Transforms a MyMessageClass instance into a byte array.
+ToProtobufTransformer toTransformer = new ToProtobufTransformer();
+
+MyMessageClass test = MyMessageClass.newBuilder()
+                                .setFoo("foo")
+                                .setBar("bar")
+                                .build();
+// message1 payload is byte array protocol buffer wire format.
+Message message1 = toTransformer.transform(new GenericMessage<>(test));
+
+// Transforms a byte array payload into a MyMessageClass instance.
+FromProtobufTransformer fromTransformer = new FromProtobufTransformer();
+
+// message2 payload == test
+Message message2 =  fromTransformer.transform(message1);
+
+----
+====
+
 [[transformer-annotation]]
 ==== Configuring a Transformer with Annotations
 

src/reference/asciidoc/whats-new.adoc

@@ -27,6 +27,10 @@ See <<./zip.adoc#zip,Zip Support>>  for more information.
 [[x6.1-general]]
 === General Changes
 
+ - Added support for transforming to/from Protocol Buffers.
+ See <<./transformer.adoc#Protobuf-transformers, Protocol Buffers Transformers>> for more information.
+
+
 [[x6.1-web-sockets]]
 === Web Sockets Changes