Spring integration: DirectChannel demo

DirectChannel invokes a single subscriber for each sent Message. For example if you have more than one subscriber, then a message is delivered the exactly one subscriber at any point of time.

 

How to messages are distributed among multiple subscribers?

Messages are distributed to multiple subscribers in round-robbin fashion by default.

 

Let’s see it with an example.

 

Step 1: Create new maven project ‘direct-channel-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>direct-channel-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 Consumer endpoints.

 

ConsumerEndpoint1.java

package com.sample.app.endpoints;

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

@Component
public class ConsumerEndpoint1 {

	@ServiceActivator(inputChannel = "directChannel")
	public Message<String> consumeMessage(Message<String> message) {
		System.out.println("ConsumerEndpoint1 -> Received message from gateway : " + message.getPayload());
		return MessageBuilder.withPayload("Message '" + message.getPayload() + "' received by ConsumerEndpoint1")
				.build();
	}

}

 

ConsumerEndpoint2.java

package com.sample.app.endpoints;

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

@Component
public class ConsumerEndpoint2 {
	
	@ServiceActivator(inputChannel = "directChannel")
	public Message<String> consumeMessage(Message<String> message) {
		System.out.println("ConsumerEndpoint2 -> Received message from gateway : " + message.getPayload());
		return MessageBuilder.withPayload("Message '" + message.getPayload() + "' received by ConsumerEndpoint2")
				.build();
	}

}

 

Step 4: Define gateway.

CustomGateway.java

package com.sample.app.endpoints;

import org.springframework.integration.annotation.Gateway;
import org.springframework.integration.annotation.MessagingGateway;
import org.springframework.messaging.Message;

@MessagingGateway(name = "myGateway", defaultRequestChannel = "directChannel")
public interface CustomGateway {

	@Gateway(requestChannel = "directChannel")
	public Message<String> print(Message<String> message);

}

 

Step 5: Define main application class.

 

App.java

 

package com.sample.app;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
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.integration.channel.DirectChannel;
import org.springframework.integration.support.MessageBuilder;
import org.springframework.messaging.Message;

import com.sample.app.endpoints.CustomGateway;

@SpringBootApplication
@Configuration
public class App {

	@Autowired
	@Qualifier("directChannel")
	private DirectChannel directChannel;

	@Autowired
	private CustomGateway customGateway;

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

	@Bean(name = "directChannel")
	public DirectChannel channel1() {
		DirectChannel channel = new DirectChannel();
		return channel;
	}

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

			for (int i = 0; i < 10; i++) {
				Message<String> message = MessageBuilder.withPayload("Msg " + i).build();
				Message<String> result = customGateway.print(message);
				System.out.println(result.getPayload());
			}

		};
	}

}

 

Total project structure looks like below.

 

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

ConsumerEndpoint1 -> Received message from gateway : Msg 0
Message 'Msg 0' received by ConsumerEndpoint1
ConsumerEndpoint2 -> Received message from gateway : Msg 1
Message 'Msg 1' received by ConsumerEndpoint2
ConsumerEndpoint1 -> Received message from gateway : Msg 2
Message 'Msg 2' received by ConsumerEndpoint1
ConsumerEndpoint2 -> Received message from gateway : Msg 3
Message 'Msg 3' received by ConsumerEndpoint2
ConsumerEndpoint1 -> Received message from gateway : Msg 4
Message 'Msg 4' received by ConsumerEndpoint1
ConsumerEndpoint2 -> Received message from gateway : Msg 5
Message 'Msg 5' received by ConsumerEndpoint2
ConsumerEndpoint1 -> Received message from gateway : Msg 6
Message 'Msg 6' received by ConsumerEndpoint1
ConsumerEndpoint2 -> Received message from gateway : Msg 7
Message 'Msg 7' received by ConsumerEndpoint2
ConsumerEndpoint1 -> Received message from gateway : Msg 8
Message 'Msg 8' received by ConsumerEndpoint1
ConsumerEndpoint2 -> Received message from gateway : Msg 9
Message 'Msg 9' received by ConsumerEndpoint2

As you see the output, Msg 0 is delivered to ConsumerEndpoint1 and Msg  1 is delivered to ConsumerEndpoint2 etc.,

 

You can download complete working application from below link.

https://github.com/harikrishna553/springboot/tree/master/spring-integration/direct-channel-demo

 

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