RabbitMQ Hello World Tutorial Using the Java Client

RabbitMQ is a message broker that receives and forwards messages, similar to a post office that stores and delivers parcels. Unlike a traditional post office, RabbitMQ stores messages in binary form without handling files.

In RabbitMQ terminology, a producer (P) sends messages, a queue stores them, and a consumer (C) receives them. Producers, consumers, and the broker can run on different machines.

The article then presents a "Hello World" example using the RabbitMQ Java client, which follows the AMQP protocol. After downloading and extracting the client JAR files, the tutorial shows how to write two Java programs: Send.java (producer) and Recv.java (consumer).

$ unzip rabbitmq-java-client-bin-*.zip
$ cp rabbitmq-java-client-bin-*/*.jar ./

Send.java imports the necessary classes, creates a connection to localhost, declares a queue named hello, publishes the message "Hello World!", prints a confirmation, and finally closes the channel and connection.

import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.Channel;

public class Send {
    private static final String QUEUE_NAME = "hello";
    public static void main(String[] argv) throws java.io.IOException {
        // ... create factory, connection, channel ...
        channel.queueDeclare(QUEUE_NAME, false, false, false, null);
        String message = "Hello World!";
        channel.basicPublish("", QUEUE_NAME, null, message.getBytes());
        System.out.println(" [x] Sent '" + message + "'");
        channel.close();
        connection.close();
    }
}

If the message is not printed, the article suggests checking the broker’s log for issues such as insufficient disk_free_limit space.

Recv.java also imports the client classes, creates a connection and channel, declares the same queue, and uses QueueingConsumer to wait for messages. It continuously receives deliveries, converts the body to a string, and prints each received message.

import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.QueueingConsumer;

public class Recv {
    private static final String QUEUE_NAME = "hello";
    public static void main(String[] argv) throws java.io.IOException, java.lang.InterruptedException {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");
        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();
        channel.queueDeclare(QUEUE_NAME, false, false, false, null);
        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");
        QueueingConsumer consumer = new QueueingConsumer(channel);
        channel.basicConsume(QUEUE_NAME, true, consumer);
        while (true) {
            QueueingConsumer.Delivery delivery = consumer.nextDelivery();
            String message = new String(delivery.getBody());
            System.out.println(" [x] Received '" + message + "'");
        }
    }
}

Both programs are compiled with the client JAR on the classpath:

$ javac -cp rabbitmq-client.jar Send.java Recv.java

They are then run (on Unix‑like systems) with:

$ java -cp .:commons-io-1.2.jar:commons-cli-1.1.jar:rabbitmq-client.jar Send
$ java -cp .:commons-io-1.2.jar:commons-cli-1.1.jar:rabbitmq-client.jar Recv

On Windows, the classpath separator is a semicolon ( ;). The receiver keeps running, waiting for messages until interrupted with Ctrl‑C. The article also mentions how to list queues using rabbitmqctl list_queues and provides a brief introduction to building a simple work queue.

Hello World!

Original source: my.oschina.net/OpenSourceBO/blog/379732