Spring integration: why there is no outbound channel adapter

An outbound channel adapter endpoint connects a MessageChannel to a target system.

 

 

Outbound channel adapter is used to send the messages from internal messaging system to external service. @ServiceActivator annotation is capable of achieving this functionality.

 

Example

@ServiceActivator(inputChannel = "notifySecretMsg")
public void notifyExternalService(String msg) {
	System.out.println("Acknowledgement received for the message '" + msg + "'");
}

How can I configure Http requests to not worry about response from external service.

Set expect reply property to false, while delivering the message to external service.

@Bean
@ServiceActivator(inputChannel = "notifySecretMsg")
public HttpRequestExecutingMessageHandler httpRequestExecutingMessageHandler() {
	HttpRequestExecutingMessageHandler handler = new HttpRequestExecutingMessageHandler();
	handler.setExpectReply(false)
    return handler;
}

Find the below working application.

 

Step 1: Create new maven project ‘outbound-adapter-demo’.

 

Step 2: Update pom.xml with maven dependencies.

 

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.sample.app</groupId>
	<artifactId>outbound-adapter-demo</artifactId>
	<version>1</version>

	<!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-parent -->
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.4.0</version>
	</parent>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-integration</artifactId>
		</dependency>

	</dependencies>

</project>

Step 3: Define service activators.

 

PrintService.java

package com.sample.app.service;

import org.springframework.integration.annotation.ServiceActivator;
import org.springframework.messaging.Message;
import org.springframework.stereotype.Component;

@Component
public class PrintService {

	@ServiceActivator(inputChannel = "secretMsgChannel", outputChannel = "notifySecretMsg")
	public String consumeStringMessage(Message<String> message) throws InterruptedException {
		System.out.println("Received message from secretMsgChannel : " + message.getPayload());

		return message.getPayload();
	}

	@ServiceActivator(inputChannel = "notifySecretMsg")
	public void notifyExternalService(String msg) {
		System.out.println("Acknowledgement received for the message '" + msg + "'");
	}
}

Step 4: Define main application.

 

App.java

package com.sample.app;

import java.util.UUID;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Configuration;
import org.springframework.integration.annotation.InboundChannelAdapter;
import org.springframework.integration.annotation.Poller;
import org.springframework.integration.support.MessageBuilder;
import org.springframework.messaging.Message;

@SpringBootApplication
@Configuration
public class App {

	@InboundChannelAdapter(channel = "secretMsgChannel", poller = {
			@Poller(maxMessagesPerPoll = "2", fixedRate = "5000") })
	Message<String> getSecretMessageFromExternalSystem() {
		UUID uuid = UUID.randomUUID();
		String secretMsg = uuid.toString();

		return MessageBuilder.withPayload(secretMsg).build();

	}

	public static void main(String[] args) {
		SpringApplication.run(App.class, args);
	}

}

Total project structure looks like below.

Run App.java, you will see below kind of messages in console.

Received message from secretMsgChannel : f319748c-dc72-4c80-8e50-0af114766cab
Acknowledgement received for the message 'f319748c-dc72-4c80-8e50-0af114766cab'
Received message from secretMsgChannel : fbc7851a-21d4-4922-94ec-ae5d02b418b7
Acknowledgement received for the message 'fbc7851a-21d4-4922-94ec-ae5d02b418b7'

 

You can download complete working application from below link.

https://github.com/harikrishna553/springboot/tree/master/spring-integration/outbound-adapter-demo

 

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Spring integration: Channel adapters

Channel adapter endpoint is used to connect a message channel to some external system.

 

There are two types of channel adapters.

 

Inbound channel adapter

An inbound channel adapter endpoint connects a source system to a MessageChannel.

 

Outbound channel adapter

An outbound channel adapter endpoint connects a MessageChannel to a target system.

 

For example, you read a message from external system using Inbound channel adapter, apply filtering, transformation and other operations on the message and send it to other external system using outbound channel adapter.

 

 

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Spring integration: Asynchronous gateways

By returning a Future or ListenableFuture from gateway method, we can make the gateway method asynchronous.

 

Step 1: Define gateway with ListenableFuture as return type.

@MessagingGateway
public interface CustomGateway {

	@Gateway(requestChannel = "printChannel")
	public ListenableFuture<String> sendToPrintChannel(String message);

}

 

Step 2: Use callback method to capture the asynchronous response.

ListenableFuture<String> reply = customGateway.sendToPrintChannel("Msg " + i);

reply.addCallback(new ListenableFutureCallback<String>() {

	@Override
	public void onSuccess(String result) {
		System.out.println(result);
	}

	@Override
	public void onFailure(Throwable ex) {
		ex.printStackTrace();
	}
});

 

Find the below working application.

 

Step 1: Create new maven project ‘asynchronous-gateway-demo’.

 

Step 2: Update pom.xml with maven dependencies.

 

pom.xml

 

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.sample.app</groupId>
	<artifactId>asynchronous-gateway-demo</artifactId>
	<version>1</version>

	<!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-parent -->
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.4.0</version>
	</parent>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-integration</artifactId>
		</dependency>

	</dependencies>

</project>

Step 3: Define service activator.

 

PrintService.java

package com.sample.app.service;

import java.util.Random;
import java.util.concurrent.TimeUnit;

import org.springframework.integration.annotation.ServiceActivator;
import org.springframework.messaging.Message;
import org.springframework.stereotype.Component;

@Component
public class PrintService {

	@ServiceActivator(inputChannel = "printChannel")
	public String consumeStringMessage(Message<String> message) throws InterruptedException {
		
		Random random = new Random();
		int timeToSleep = random.nextInt(10);
		
		TimeUnit.SECONDS.sleep(timeToSleep);
		
		System.out.println("Received message from printChannel : " + message.getPayload());		
		return "Message " + message.getPayload() + " received";
	}
	

}

Step 4: Define gateway.

 

CustomGateway.java

package com.sample.app.gateway;

import org.springframework.integration.annotation.Gateway;
import org.springframework.integration.annotation.MessagingGateway;
import org.springframework.util.concurrent.ListenableFuture;

@MessagingGateway
public interface CustomGateway {

	@Gateway(requestChannel = "printChannel")
	public ListenableFuture<String> sendToPrintChannel(String message);

}

 

Step 5: Define main application class.

 

App.java

 

package com.sample.app;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.util.concurrent.ListenableFutureCallback;

import com.sample.app.gateway.CustomGateway;

@SpringBootApplication
@Configuration
public class App {

	@Autowired
	private CustomGateway customGateway;

	public static void main(String[] args) {
		SpringApplication.run(App.class, args);
	}

	@Bean
	public CommandLineRunner demo() {
		return (args) -> {

			for (int i = 0; i < 5; i++) {
				ListenableFuture<String> reply = customGateway.sendToPrintChannel("Msg " + i);

				reply.addCallback(new ListenableFutureCallback<String>() {

					@Override
					public void onSuccess(String result) {
						System.out.println(result);
					}

					@Override
					public void onFailure(Throwable ex) {
						ex.printStackTrace();
					}
				});
			}

		};

	};

}

 

Total project structure looks like below.

 

 

Run App.java, you will see below kind of messages in console.

 

Received message from printChannel : Msg 1
Message Msg 1 received
Received message from printChannel : Msg 4
Message Msg 4 received
Received message from printChannel : Msg 0
Message Msg 0 received
Received message from printChannel : Msg 2
Message Msg 2 received
Received message from printChannel : Msg 3
Message Msg 3 received

 

You can download complete working application from below link.

https://github.com/harikrishna553/springboot/tree/master/spring-integration/asynchronous-gateway-demo

 

 

 

 

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Spring integration: GatewayHeader: Add headers at Gateway

You can add headers to a message using gateway.

 

How to add headers using @MessagingGateway annotation

‘defaultHeaders’ attribute is used to custom message headers. These default headers are created for all methods on the service-interface.

 

Example

@MessagingGateway(defaultHeaders = {@GatewayHeader(name = "root-header", value = "root123")})
public interface CustomGateway {

}

How to add headers using @Gateway annotation?

'headers' attribute is used specify additional headers that will be added to the request message.

@Gateway(requestChannel = "printChannel", headers = {
		@GatewayHeader(name = "secret", value = "my-secret123"),
		@GatewayHeader(name = "service-name", value = "my-service") })
public String sendToPrintChannel(String message);

 

Find the below working application.

 

Step 1: Create new maven project ‘gateway-headers-demo’.

 

Step 2: Update pom.xml with maven dependencies.

 

pom.xml

 

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.sample.app</groupId>
	<artifactId>gateway-headers-demo</artifactId>
	<version>1</version>

	<!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-parent -->
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.4.0</version>
	</parent>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-integration</artifactId>
		</dependency>

	</dependencies>

</project>

Step 3: Define gateway.

 

CustomGateway.java

package com.sample.app.gateway;

import org.springframework.integration.annotation.Gateway;
import org.springframework.integration.annotation.MessagingGateway;
import org.springframework.integration.annotation.*;

@MessagingGateway(defaultHeaders = {@GatewayHeader(name = "root-header", value = "root123")})
public interface CustomGateway {

	@Gateway(requestChannel = "printChannel", headers = {
			@GatewayHeader(name = "secret", value = "my-secret123"),
			@GatewayHeader(name = "service-name", value = "my-service") })
	public String sendToPrintChannel(String message);

}

Step 4: Define service activator.

 

PrintService.java

package com.sample.app.service;

import java.util.Map;
import java.util.Set;

import org.springframework.integration.annotation.ServiceActivator;
import org.springframework.messaging.Message;
import org.springframework.stereotype.Component;

@Component
public class PrintService {

	@ServiceActivator(inputChannel = "printChannel")
	public String consumeStringMessage(Message<String> message) {
		System.out.println("Received message from printChannel : " + message.getPayload());
		
		Set<Map.Entry<String, Object>> messageHeaders = message.getHeaders().entrySet();
		
		System.out.println("Headers are.....");
		for(Map.Entry<String, Object> entry: messageHeaders) {
			System.out.println(entry.getKey() + " -> " + entry.getValue());
		}
		
		return "Success";
	}
	

}

Step 5: Define main application class.

 

App.java

package com.sample.app;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.sample.app.gateway.CustomGateway;

@SpringBootApplication
@Configuration
public class App {

	@Autowired
	private CustomGateway customGateway;

	public static void main(String[] args) {
		SpringApplication.run(App.class, args);
	}

	@Bean
	public CommandLineRunner demo() {
		return (args) -> {

			String reply = customGateway.sendToPrintChannel("Hello World");
			
			System.out.println("reply : " + reply);
		};

	};

}

Total project structure looks like below.

Run App.java, you will see below messages in console.

Received message from printChannel : Hello World
Headers are.....
service-name -> my-service
replyChannel -> org.springframework.messaging.core.GenericMessagingTemplate$TemporaryReplyChannel@64712be
errorChannel -> org.springframework.messaging.core.GenericMessagingTemplate$TemporaryReplyChannel@64712be
root-header -> root123
secret -> my-secret123
id -> f3f45661-6f2e-b0c4-5503-04c302aeb937
timestamp -> 1617701164345
reply : Success

You can download complete working application from below link.

https://github.com/harikrishna553/springboot/tree/master/spring-integration/gateway-headers-demo

 

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