Spring Integration- Chanels

In this example, we’ll use the DirectChannel to subscribe to those channels.

PrintService.java

import java.util.Map.Entry;

import org.springframework.messaging.Message;
import org.springframework.messaging.MessageHeaders;

public class PrintService {

   public void print(Message<String> message){
      MessageHeaders headers = message.getHeaders();
      for(Entry<String,Object> entry:headers.entrySet()){
         System.out.println("Key >> "+ entry.getKey()+":: Value >> "+ entry.getValue());
      }
      System.out.println(message.getPayload());
   }
}

MainApp.java

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ImportResource;
import org.springframework.integration.channel.DirectChannel;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageHandler;
import org.springframework.messaging.MessagingException;
import org.springframework.messaging.support.MessageBuilder;

@SpringBootApplication
@Configuration
@ImportResource("integration-context.xml")
public class SpringIntegrationApplication implements ApplicationRunner {

    @Autowired
    private DirectChannel channel;

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

    @Override
    public void run(ApplicationArguments arg0) {

        // Subscribe to those message
        channel.subscribe(new MessageHandler() {
            @Override
            public void handleMessage(Message<?> message) throws MessagingException {
                System.out.println("Message subscribed are -- ");
                new PrintService().print((Message<String>) message);
            }
        });

        // Send the message!
        Message<String> message = MessageBuilder
                .withPayload("Hello World, from the builder pattern")
                .setHeader("newHeader", "newHeaderValue")
                .build();
        channel.send(message);
    }
}

integration-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:int="http://www.springframework.org/schema/integration"
   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/integration http://www.springframework.org/schema/integration/spring-integration-4.2.xsd">

   <int:channel id="messageChannel"/>
   
</beans>

Output —

Message subscribed are —
Key >> newHeader:: Value >> newHeaderValue
Key >> id:: Value >> 491e23d3–7fd6-ac6e-23b7–58cf4710e32a
Key >> timestamp:: Value >> 1639325869520
Hello World, from the builder pattern