Add gRPC server and client samples with Spring Integration

basic/grpc-client/README.md

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+gRPC Client Sample
+==================
+
+This sample demonstrates how to use Spring Integration's gRPC support with an **Outbound Gateway** to make gRPC requests to a server.
+
+The sample implements a gRPC client that calls a `HelloWorldService` demonstrating different communication patterns:
+
+* **SayHello** - Unary RPC (single request, single response)
+* **StreamSayHello** - Server streaming RPC (single request, multiple responses)
+
+The client automatically executes both examples on startup using `ApplicationRunner` beans.
+
+## Running the Sample
+
+**Important:** Start the gRPC server first (see the grpc-server sample) and it must have the same gRPC proto files as the client.
+
+Then start the gRPC client using Gradle:
+
+    $ gradlew :grpc-client:bootRun
+
+#### Using an IDE such as SpringSource Tool Suite™ (STS)
+
+In STS (Eclipse), go to package **org.springframework.integration.samples.grpc**, right-click **Application** and select **Run as** --> **Java Application** (or Spring Boot Application).
+
+### Output
+
+The client will automatically send requests to the server and display the responses:
+
+```
+Single response reply: message: "Hello Jack"
+
+Stream received reply: Hello Jack
+Stream received reply: Hello again!
+```
+
+## Configuration
+
+The gRPC server connection is configured in `application.properties`:
+
+```properties
+grpc.server.host=localhost
+grpc.server.port=9090
+```
+
+## Resources
+
+* [Spring Integration gRPC Documentation](https://docs.spring.io/spring-integration/reference/grpc.html)

basic/grpc-client/src/main/java/org/springframework/integration/samples/grpc/Application.java

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+/*
+ * Copyright 2026-present 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.samples.grpc;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+/**
+ * Main application class for the gRPC client sample.
+ * This Spring Boot application demonstrates how to use Spring Integration
+ * with gRPC for client-side communication.
+ *
+ * @author Glenn Renfro
+ */
+@SpringBootApplication
+public final class Application {
+
+	private Application() {
+	}
+
+	/**
+	 * Main entry point for the gRPC client application.
+	 *
+	 * @param args command line arguments
+	 */
+	public static void main(String[] args) {
+		SpringApplication.run(Application.class, args);
+	}
+
+}

basic/grpc-client/src/main/java/org/springframework/integration/samples/grpc/configuration/ClientHelloWorldConfiguration.java

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+/*
+ * Copyright 2026-present 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.samples.grpc.configuration;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import io.grpc.ManagedChannel;
+import io.grpc.ManagedChannelBuilder;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import reactor.core.publisher.Flux;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.ApplicationRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.integration.channel.DirectChannel;
+import org.springframework.integration.channel.FluxMessageChannel;
+import org.springframework.integration.channel.QueueChannel;
+import org.springframework.integration.dsl.IntegrationFlow;
+import org.springframework.integration.grpc.dsl.Grpc;
+import org.springframework.integration.grpc.outbound.GrpcOutboundGateway;
+import org.springframework.integration.grpc.proto.HelloReply;
+import org.springframework.integration.grpc.proto.HelloRequest;
+import org.springframework.integration.grpc.proto.HelloWorldServiceGrpc;
+import org.springframework.integration.support.MessageBuilder;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageChannel;
+
+/**
+ * Configuration class for the gRPC client sample.
+ * Configures the gRPC channel, message channels, and integration flows
+ * for both single response and streaming response scenarios.
+ *
+ * @author Glenn Renfro
+ */
+@Configuration
+class ClientHelloWorldConfiguration {
+
+	private static final Log LOG = LogFactory.getLog(ClientHelloWorldConfiguration.class);
+
+	/**
+	 * Creates a managed gRPC channel for communication with the server.
+	 *
+	 * @param host the gRPC server host (default: localhost)
+	 * @param port the gRPC server port (default: 9090)
+	 * @return the configured managed channel
+	 */
+	@Bean(destroyMethod = "shutdownNow")
+	ManagedChannel managedChannel(@Value("${grpc.server.host:localhost}") String host,
+			@Value("${grpc.server.port:9090}") int port) {
+		return ManagedChannelBuilder.forAddress(host, port)
+				.usePlaintext()
+				.build();
+	}
+
+	/**
+	 * Creates a message channel for single response gRPC requests.
+	 *
+	 * @return the direct message channel
+	 */
+	@Bean
+	MessageChannel grpcInputChannelSingleResponse() {
+		return new DirectChannel();
+	}
+
+	/**
+	 * Creates a message channel for streaming response gRPC requests.
+	 *
+	 * @return the direct message channel
+	 */
+	@Bean
+	MessageChannel grpcInputChannelStreamResponse() {
+		return new DirectChannel();
+	}
+
+	/**
+	 * Creates a FluxMessageChannel for output.
+	 *
+	 * @return the flux message channel
+	 */
+	@Bean
+	FluxMessageChannel grpcStreamOutputChannel() {
+		return new FluxMessageChannel();
+	}
+
+	/**
+	 * Creates an application runner that sends a single gRPC request and receives a single response.
+	 *
+	 * @param grpcInputChannelSingleResponse the message channel for single response requests
+	 * @param replyTimeout the time in milliseconds to await for the response.  Defaults to 10,000 milliseconds.
+	 * @return the application runner
+	 */
+	@Bean
+	ApplicationRunner grpcClientSingleResponse(MessageChannel grpcInputChannelSingleResponse,
+			@Value("${grpc.client.single.reply.timeout:10000}") long replyTimeout) {
+		return args -> {
+			HelloRequest request = HelloRequest.newBuilder().setName("Jack").build();
+			QueueChannel replyChannel = new QueueChannel();
+			Message<?> requestMessage = MessageBuilder.withPayload(request)
+					.setReplyChannel(replyChannel)
+					.build();
+			grpcInputChannelSingleResponse.send(requestMessage);
+			Message<?> reply = replyChannel.receive(replyTimeout);
+			if (reply != null) {
+				LOG.info("Single response reply: " + reply.getPayload());
+			}
+			else {
+				LOG.warn("No reply received");
+			}
+		};
+	}
+
+	/**
+	 * Creates an application runner that sends a gRPC request and receives a stream of responses.
+	 *
+	 * @param grpcInputChannelStreamResponse the message channel for streaming response requests
+	 * @param grpcStreamOutputChannel channel that contains the responses
+	 * @param replyTimeout the time in seconds to await for the response.  Defaults to 1 second.
+	 * @return the application runner
+	 */
+	@Bean
+	ApplicationRunner grpcClientStreamResponse(MessageChannel grpcInputChannelStreamResponse,
+			FluxMessageChannel grpcStreamOutputChannel,
+			@Value("${grpc.client.stream.reply.timeout:1}") int replyTimeout) {
+		return args -> {
+			CountDownLatch latch = new CountDownLatch(1);
+
+			Flux.from(grpcStreamOutputChannel)
+					.doOnSubscribe(subscription -> {
+						HelloRequest request = HelloRequest.newBuilder().setName("Jack").build();
+						Message<?> requestMessage = MessageBuilder.withPayload(request).build();
+						grpcInputChannelStreamResponse.send(requestMessage);
+					})
+					.map(message -> (HelloReply) message.getPayload())
+					.map(HelloReply::getMessage)
+					.doOnNext(msg -> LOG.info("Stream received reply: " + msg))
+					.doOnComplete(latch::countDown)
+					.doOnError(error -> {
+						LOG.error("Error in stream: " + error.getMessage(), error);
+						latch.countDown();
+					})
+					.subscribe();
+
+			latch.await(replyTimeout, TimeUnit.SECONDS);
+		};
+	}
+
+	/**
+	 * Creates an integration flow for outbound gRPC requests with single responses.
+	 *
+	 * @param managedChannel the gRPC managed channel
+	 * @param grpcInputChannelSingleResponse the input message channel
+	 * @return the integration flow
+	 */
+	@Bean
+	IntegrationFlow grpcOutboundFlowSingleResponse(ManagedChannel managedChannel,
+			MessageChannel grpcInputChannelSingleResponse) {
+		return IntegrationFlow.from(grpcInputChannelSingleResponse)
+				.handle(Grpc.outboundGateway(managedChannel, HelloWorldServiceGrpc.class)
+						.methodName("SayHello"))
+				.get();
+	}
+
+	/**
+	 * Creates an integration flow for outbound gRPC requests with streaming responses.
+	 *
+	 * @param managedChannel the gRPC managed channel
+	 * @param grpcInputChannelStreamResponse the input message channel
+	 * @param grpcStreamOutputChannel channel containing the results
+	 * @return the integration flow
+	 */
+	@Bean
+	IntegrationFlow grpcOutboundFlowStreamResponse(ManagedChannel managedChannel,
+			MessageChannel grpcInputChannelStreamResponse,
+			FluxMessageChannel grpcStreamOutputChannel) {
+		//TODO: Need advice, there has to be a better way than what I have below (or is this a bug in the
+		// GrpcOutboundGateway?
+		GrpcOutboundGateway gateway = new GrpcOutboundGateway(managedChannel, HelloWorldServiceGrpc.class) {
+			@Override
+			protected boolean shouldSplitOutput(Iterable<?> reply) {
+				return false;
+			}
+		};
+		gateway.setMethodName("StreamSayHello");
+		gateway.setAsync(true);
+
+		return IntegrationFlow.from(grpcInputChannelStreamResponse)
+				.handle(gateway)
+				.channel(grpcStreamOutputChannel)
+				.get();
+	}
+
+}

basic/grpc-client/src/main/proto/hello.proto

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+syntax = "proto3";
+import "types.proto";
+
+package integration.grpc.hello;
+
+option java_package = "org.springframework.integration.grpc.proto";
+
+option java_multiple_files = true;
+
+option java_outer_classname = "HelloWorldProto";
+
+// The greeting service definition.
+service HelloWorldService {
+
+  // Sends a greeting
+  rpc SayHello(HelloRequest) returns (HelloReply) {}
+
+  // Sends a greeting and something else
+  rpc StreamSayHello(HelloRequest) returns (stream HelloReply) {}
+
+  // Sends a greeting to everyone presenting
+  rpc HelloToEveryOne(stream HelloRequest) returns (HelloReply) {}
+
+  // Streams requests and replies
+  rpc BidiStreamHello(stream HelloRequest) returns (stream HelloReply) {}
+
+}

basic/grpc-client/src/main/proto/types.proto

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+syntax = "proto3";
+
+package integration.grpc.hello;
+
+option java_package = "org.springframework.integration.grpc.proto";
+
+option java_multiple_files = true;
+
+option java_outer_classname = "TypesProto";
+
+// The request message containing the user's name.
+message HelloRequest {
+
+  string name = 1;
+
+}
+
+// The response message containing the greetings
+message HelloReply {
+
+  string message = 1;
+
+}

basic/grpc-client/src/main/resources/application.properties

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+grpc.server.host=localhost
+grpc.server.port=9090
+grpc.client.stream.reply.timeout=1
+grpc.client.single.reply.timeout=10000