Camel: Multicasting the messages to different destinations

Camel support multicasting of the messages to different destinations.

Let’s implement an example like below.

a.   Copy the files from local file system to an ActiveMQ queue ‘A’.

b.   Multicast all the data from queue ‘A’ to other Queues B, C, D.

Setup ActiveMQ

I would recommend you to go through my below post to setup the activeMQ.

https://self-learning-java-tutorial.blogspot.com/2018/08/installing-and-setting-up-activemq.html

Once you setup activeMQ, loginto the admin console by hitting below url.

http://localhost:8161/admin/

Use below credentials to login to the admin console.

UserName: admin

Password: admin

You can see below kind of user interface.

Setup Eclipse Maven Project

Create new maven project 'camelMultiCasting'. Project structure looks like below.

Open pom.xml and update 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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>camelMultiCasting</groupId>
	<artifactId>camelMultiCasting</artifactId>
	<version>1</version>


	<dependencies>
		<!-- https://mvnrepository.com/artifact/org.apache.camel/camel-jms -->
		<dependency>
			<groupId>org.apache.camel</groupId>
			<artifactId>camel-jms</artifactId>
			<version>2.22.1</version>
		</dependency>

		<!-- https://mvnrepository.com/artifact/org.apache.camel/camel-core -->
		<dependency>
			<groupId>org.apache.camel</groupId>
			<artifactId>camel-core</artifactId>
			<version>2.22.1</version>
		</dependency>

		<!-- https://mvnrepository.com/artifact/org.apache.activemq/activemq-all -->
		<dependency>
			<groupId>org.apache.activemq</groupId>
			<artifactId>activemq-all</artifactId>
			<version>5.15.6</version>
		</dependency>

	</dependencies>
</project>

Below statement moves the files from local folder to queue1 and then multicast all the items in queue to queue2, queue3, queue4.

from("file:C:\\Users\\Public\\demo?noop=true").to(queue1).multicast().to(queue2, queue3, queue4);

Create new package 'com.sample.app.routes' and define the class FileCopyRoute.

FileCopyRoute.java

package com.sample.app.routes;

import org.apache.camel.Exchange;
import org.apache.camel.Processor;
import org.apache.camel.builder.RouteBuilder;

public class FileCopyRoute extends RouteBuilder {

	@Override
	public void configure() throws Exception {
		String queue1 = "demoJMS:queue:A";
		String queue2 = "demoJMS:queue:B";
		String queue3 = "demoJMS:queue:C";
		String queue4 = "demoJMS:queue:D";

		from("file:C:\\Users\\Public\\demo?noop=true").to(queue1).multicast().to(queue2, queue3, queue4);

		from(queue2).process(new Processor() {
			@Override
			public void process(Exchange exchange) throws Exception {
				String fileName = (String) exchange.getIn().getHeader("CamelFileName");
				System.out.println("Queue2 received " + fileName);

			}
		});

		from(queue3).process(new Processor() {
			@Override
			public void process(Exchange exchange) throws Exception {
				String fileName = (String) exchange.getIn().getHeader("CamelFileName");
				System.out.println("Queue3 received " + fileName);

			}
		});

		from(queue4).process(new Processor() {
			@Override
			public void process(Exchange exchange) throws Exception {
				String fileName = (String) exchange.getIn().getHeader("CamelFileName");
				System.out.println("Queue4 received " + fileName);

			}
		});
	}
}

Application.java

package com.sample.app;

import java.util.concurrent.TimeUnit;

import javax.jms.ConnectionFactory;

import org.apache.activemq.ActiveMQConnectionFactory;
import org.apache.camel.CamelContext;
import org.apache.camel.component.jms.JmsComponent;
import org.apache.camel.impl.DefaultCamelContext;

import com.sample.app.routes.FileCopyRoute;

public class Application {
	public static void main(String args[]) throws Exception {
		CamelContext context = new DefaultCamelContext();

		ConnectionFactory connectionFactory = new ActiveMQConnectionFactory("tcp://localhost:61616");

		context.addComponent("demoJMS", JmsComponent.jmsComponentAutoAcknowledge(connectionFactory));

		context.addRoutes(new FileCopyRoute());

		context.start();

		TimeUnit.MINUTES.sleep(1);

		context.stop();
	}
}

In my case ‘demo’ folder has below documents.

BigFile.txt

Chapter1.docx

Hello.bat

sales.xlsx

SmallFile.txt

Run Application.java, you can see below messages in the console.

Queue2 received BigFile.txt

Queue3 received BigFile.txt

Queue4 received BigFile.txt

Queue2 received Chapter1.docx

Queue3 received Chapter1.docx

Queue4 received Chapter1.docx

Queue2 received Hello.bat

Queue3 received Hello.bat

Queue4 received Hello.bat

Queue2 received sales.xlsx

Queue3 received sales.xlsx

Queue4 received sales.xlsx

Queue2 received SmallFile.txt

Queue3 received SmallFile.txt

Queue4 received SmallFile.txt

See the above image, Queue A has 5 messages, but Queues B, C, and D has 0 pending messages. It is because, we processed the messages from B, C, D queues (while printing), but not from Queue A.

One more thing, when you observe the console output, messages are transmitted sequentially. If you want parallel behavior, you can use parallelProcessing() function.

from("file:C:\\Users\\Public\\demo?noop=true")

         .to(queue1)

         .multicast()

         .parallelProcessing()

         .to(queue2, queue3,queue4);

FileCopyRoute.java

package com.sample.app.routes;

import org.apache.camel.Exchange;
import org.apache.camel.Processor;
import org.apache.camel.builder.RouteBuilder;

public class FileCopyRoute extends RouteBuilder {

	@Override
	public void configure() throws Exception {
		String queue1 = "demoJMS:queue:A";
		String queue2 = "demoJMS:queue:B";
		String queue3 = "demoJMS:queue:C";
		String queue4 = "demoJMS:queue:D";

		from("file:C:\\Users\\Public\\demo?noop=true").to(queue1).multicast().parallelProcessing().to(queue2, queue3,
				queue4);

		from(queue2).process(new Processor() {
			@Override
			public void process(Exchange exchange) throws Exception {
				String fileName = (String) exchange.getIn().getHeader("CamelFileName");
				System.out.println("Queue2 received " + fileName);

			}
		});

		from(queue3).process(new Processor() {
			@Override
			public void process(Exchange exchange) throws Exception {
				String fileName = (String) exchange.getIn().getHeader("CamelFileName");
				System.out.println("Queue3 received " + fileName);

			}
		});

		from(queue4).process(new Processor() {
			@Override
			public void process(Exchange exchange) throws Exception {
				String fileName = (String) exchange.getIn().getHeader("CamelFileName");
				System.out.println("Queue4 received " + fileName);

			}
		});
	}
}

Rerun Application.java, you can see the parallel behavior in message transmission. In my case, I seen below messages in console.

Queue2 received BigFile.txt

Queue4 received BigFile.txt

Queue3 received BigFile.txt

Queue3 received Chapter1.docx

Queue2 received Chapter1.docx

Queue4 received Chapter1.docx

Queue4 received Hello.bat

Queue2 received Hello.bat

Queue3 received Hello.bat

Queue3 received sales.xlsx

Queue4 received sales.xlsx

Queue2 received sales.xlsx

Queue4 received SmallFile.txt

Queue2 received SmallFile.txt

Queue3 received SmallFile.txt

When you request camel to perform parallel processing, camel use a default thread pool of size 10. You can even pass another thread pool to perform this task by calling executorService() method.

ExecutorService executor = Executors.newFixedThreadPool(20);

from("file:C:\\Users\\Public\\demo?noop=true")

         .to(queue1)

         .multicast()

         .parallelProcessing()

         .executorService(executor)

         .to(queue2, queue3, queue4);

Above snippet increase the maximum number of threads to 20.

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