DirectChannel invokes a single subscriber for each sent Message. For example if you have more than one subscriber to a direct channel, 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.
How can I specify the order of distribution?
As you see above image, there are three endpoints subscribed to direct channel and I want message 0 to be sent to endpoint2, message 1 to endpoint3 and message 2 to endpoint1.
I can achieve this by adding @Order alongside with those Messaging annotations.
Example
@Component
public class ConsumerEndpoint1 {
@ServiceActivator(inputChannel = "directChannel")
@Order(3)
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();
}
}
Find the below working application.
Step 1: Create new maven project ‘direct-channel-consumption-order-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-consumption-order-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 endpoint.
ConsumerEndpoint1.java
package com.sample.app.endpoints;
import org.springframework.core.annotation.Order;
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")
@Order(3)
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.core.annotation.Order;
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")
@Order(1)
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();
}
}
ConsumerEndpoint3.java
package com.sample.app.endpoints;
import org.springframework.core.annotation.Order;
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 ConsumerEndpoint3 {
@ServiceActivator(inputChannel = "directChannel")
@Order(2)
public Message<String> consumeMessage(Message<String> message) {
System.out.println("ConsumerEndpoint3 -> Received message from gateway : " + message.getPayload());
return MessageBuilder.withPayload("Message '" + message.getPayload() + "' received by ConsumerEndpoint3")
.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.
ConsumerEndpoint2 -> Received message from gateway : Msg 0 Message 'Msg 0' received by ConsumerEndpoint2 ConsumerEndpoint3 -> Received message from gateway : Msg 1 Message 'Msg 1' received by ConsumerEndpoint3 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 ConsumerEndpoint3 -> Received message from gateway : Msg 4 Message 'Msg 4' received by ConsumerEndpoint3 ConsumerEndpoint1 -> Received message from gateway : Msg 5 Message 'Msg 5' received by ConsumerEndpoint1 ConsumerEndpoint2 -> Received message from gateway : Msg 6 Message 'Msg 6' received by ConsumerEndpoint2 ConsumerEndpoint3 -> Received message from gateway : Msg 7 Message 'Msg 7' received by ConsumerEndpoint3 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
You can download complete working application from below link.
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