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RabbitMQ Introduction

  1. What Is RabbitMQ?



  2. Core Concepts in RabbitMQ



  3. RabbitMQ Exchange Types



  4. Message Flow in RabbitMQ



  5. RabbitMQ vs Kafka (High-Level)



  6. Installing and Running RabbitMQ



  7. Basic Python Producer and Consumer Example



  8. RabbitMQ Acknowledgements

    9. channel.basic_consume(queue='jobs', on_message_callback=callback, auto_ack=False)


  9. Durable Queues & Persistent Messages

    10. channel.queue_declare(queue='jobs', durable=True)
channel.basic_publish(exchange='', routing_key='jobs',
                      body='hello',
                      properties=pika.BasicProperties(delivery_mode=2))


RabbitMQ — Hello World with the Java Client

  1. This chapter explains how to build a minimal Hello World message queue using:


  2. Prerequisites



  3. Project Structure



  4. Adding the RabbitMQ Java Client Dependency (Maven)



  5. Understanding the Connection to RabbitMQ



  6. Sender — Send.java

    7. package com.example;

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

import java.nio.charset.StandardCharsets;

public class Send {

    private static final String QUEUE_NAME = "hello";

    public static void main(String[] args) throws Exception {
        // 1. Create a connection factory and configure it
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");
        // factory.setUsername("guest");
        // factory.setPassword("guest");

        // 2. Create connection and channel using try-with-resources
        try (Connection connection = factory.newConnection();
             Channel channel = connection.createChannel()) {

            // 3. Declare the queue (idempotent — only created if it does not exist)
            channel.queueDeclare(
                    QUEUE_NAME,
                    false,  // durable
                    false,  // exclusive
                    false,  // autoDelete
                    null    // arguments
            );

            // 4. Message to send
            String message = "Hello World from Java!";

            // 5. Publish the message to the default exchange ("") with routing key = queue name
            channel.basicPublish(
                    "",
                    QUEUE_NAME,
                    null,
                    message.getBytes(StandardCharsets.UTF_8)
            );

            System.out.println(" [x] Sent '" + message + "'");
        } // END try
    }
}


  7. Receiver — Recv.java

    8. package com.example;

import com.rabbitmq.client.*;

import java.nio.charset.StandardCharsets;

public class Recv {

    private static final String QUEUE_NAME = "hello";

    public static void main(String[] args) throws Exception {
        // 1. Create connection factory
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");
        // factory.setUsername("guest");
        // factory.setPassword("guest");

        // 2. Create connection and channel
        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        // 3. Ensure the same queue exists
        channel.queueDeclare(
                QUEUE_NAME,
                false,
                false,
                false,
                null
        );

        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");

        // 4. Define how to process delivered messages (callback)
        DeliverCallback deliverCallback = (consumerTag, delivery) -> {
            String message = new String(
                    delivery.getBody(),
                    StandardCharsets.UTF_8
            );
            System.out.println(" [x] Received '" + message + "'");
        };

        CancelCallback cancelCallback = consumerTag -> {
            System.out.println(" [!] Consumer was cancelled: " + consumerTag);
        };

        // 5. Start consuming messages (autoAck = true)
        channel.basicConsume(
                QUEUE_NAME,
                true,            // autoAck
                deliverCallback,
                cancelCallback
        );
    }
}


  8. Building and Running the Example



  9. How the Visually Message Flow Works
    10. [Send.java] --basicPublish--> [""] default exchange --> [queue "hello"] --> [Recv.java]


  10. Common Troubleshooting Tips



RabbitMQ — Work Queues (Using the Java Client)

  1. What Are Work Queues?



  2. Project Structure
    3. rabbitmq-work-queues/
├─ pom.xml
└─ src/
   └─ main/
      └─ java/
         └─ com/
            └─ example/
               ├─ NewTask.java   <-- producer (sends tasks)
               └─ Worker.java    <-- worker (receives tasks)


  3. Declaring a Durable Queue
    4. boolean durable = true;
channel.queueDeclare("task_queue", durable, false, false, null);


  4. Producer (NewTask.java)



  5. Worker (Worker.java)

    6. package com.example;

import com.rabbitmq.client.*;

public class Worker {

    private static final String QUEUE_NAME = "task_queue";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        // Durable queue
        boolean durable = true;
        channel.queueDeclare(QUEUE_NAME, durable, false, false, null);

        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");

        // Fair dispatch: don't give new messages until worker is done
        channel.basicQos(1);

        // Define callback for messages
        DeliverCallback deliverCallback = (consumerTag, delivery) -> {
            String message = new String(delivery.getBody(), "UTF-8");
            System.out.println(" [x] Received '" + message + "'");

            try {
                doWork(message);
            } finally {
                System.out.println(" [x] Done");
                channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
            }
        };

        // AutoAck = false → manual acknowledgements
        boolean autoAck = false;

        channel.basicConsume(QUEUE_NAME, autoAck, deliverCallback, consumerTag -> { });
    }

    private static void doWork(String task) {
        for (char ch : task.toCharArray()) {
            if (ch == '.') {
                try {
                    Thread.sleep(1000); // one second per dot
                } catch (InterruptedException ignored) {}
            }
        }
    }
}


  6. Running Multiple Workers



  7. How Acknowledgements Work



  8. Message Durability



  9. Fair Dispatch with basicQos(1)



RabbitMQ — Publish/Subscribe (Using the Java Client)

  1. What Is Publish/Subscribe?



  2. Core Concepts: Exchange & Fanout



  3. Project Structure
    4. rabbitmq-pubsub-java/
├─ pom.xml
└─ src/
   └─ main/
      └─ java/
         └─ com/
            └─ example/
               ├─ EmitLog.java       <-- producer (publishes logs)
               └─ ReceiveLogs.java   <-- consumer (subscribes to logs)

    <dependency>
    <groupId>com.rabbitmq</groupId>
    <artifactId>amqp-client</artifactId>
    <version>5.24.0</version>
</dependency>


  4. Declaring the Fanout Exchange

    5. String EXCHANGE_NAME = "logs";
channel.exchangeDeclare(EXCHANGE_NAME, BuiltinExchangeType.FANOUT);



  5. Producer — EmitLog.java

    6. package com.example;

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

import java.nio.charset.StandardCharsets;

public class EmitLog {

    private static final String EXCHANGE_NAME = "logs";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        try (Connection connection = factory.newConnection();
             Channel channel = connection.createChannel()) {

            // Declare fanout exchange
            channel.exchangeDeclare(EXCHANGE_NAME, BuiltinExchangeType.FANOUT);

            // Build message from command-line arguments
            String message = String.join(" ", argv);
            if (message.isEmpty()) {
                message = "info: Hello RabbitMQ Publish/Subscribe!";
            }

            // Publish to exchange (routing key is ignored by fanout)
            channel.basicPublish(
                    EXCHANGE_NAME,
                    "",
                    null,
                    message.getBytes(StandardCharsets.UTF_8)
            );

            System.out.println(" [x] Sent '" + message + "'");
        }
    }
}


  6. Consumer — ReceiveLogs.java (Ephemeral Queues)

    7. package com.example;

import com.rabbitmq.client.*;

import java.nio.charset.StandardCharsets;

public class ReceiveLogs {

    private static final String EXCHANGE_NAME = "logs";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        // Declare fanout exchange
        channel.exchangeDeclare(EXCHANGE_NAME, BuiltinExchangeType.FANOUT);

        // Create a non-durable, exclusive, auto-delete queue with a generated name
        String queueName = channel.queueDeclare().getQueue();

        // Bind the queue to the exchange
        channel.queueBind(queueName, EXCHANGE_NAME, "");

        System.out.println(" [*] Waiting for logs in queue '" + queueName +
                           "'. To exit press CTRL+C");

        // Define callback
        DeliverCallback deliverCallback = (consumerTag, delivery) -> {
            String message = new String(
                    delivery.getBody(),
                    StandardCharsets.UTF_8
            );
            System.out.println(" [x] Received '" + message + "'");
        };

        CancelCallback cancelCallback = consumerTag -> {
            System.out.println(" [!] Consumer cancelled: " + consumerTag);
        };

        // Start consuming (autoAck = true)
        boolean autoAck = true;
        channel.basicConsume(queueName, autoAck, deliverCallback, cancelCallback);
    }
}


  7. Running Multiple Subscribers



  8. Temporary vs Persistent Subscribers



  9. How Publish/Subscribe Differs from Work Queues



RabbitMQ — Routing (Using the Java Client)

  1. What Is Routing with Direct Exchanges?



  2. Direct Exchange and Routing Keys



  3. Project Structure

    4. rabbitmq-routing-java/
├─ pom.xml
└─ src/
   └─ main/
      └─ java/
         └─ com/
            └─ example/
               ├─ EmitLogDirect.java
               └─ ReceiveLogsDirect.java

    <dependency>
    <groupId>com.rabbitmq</groupId>
    <artifactId>amqp-client</artifactId>
    <version>5.24.0</version>
</dependency>


  4. Declaring the Direct Exchange

    5. String EXCHANGE_NAME = "direct_logs";
channel.exchangeDeclare(EXCHANGE_NAME, BuiltinExchangeType.DIRECT);


  5. Producer — EmitLogDirect.java

    6. package com.example;

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

import java.nio.charset.StandardCharsets;

public class EmitLogDirect {

    private static final String EXCHANGE_NAME = "direct_logs";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        try (Connection connection = factory.newConnection();
             Channel channel = connection.createChannel()) {

            // Declare direct exchange
            channel.exchangeDeclare(EXCHANGE_NAME, BuiltinExchangeType.DIRECT);

            // Severity (routing key)
            String severity = argv.length > 0 ? argv[0] : "info";

            // Message text
            String message;
            if (argv.length > 1) {
                StringBuilder builder = new StringBuilder();
                for (int i = 1; i < argv.length; i++) {
                    if (i > 1) {
                        builder.append(" ");
                    }
                    builder.append(argv[i]);
                }
                message = builder.toString();
            } else {
                message = "Hello from direct routing!";
            }

            // Publish with routing key = severity
            channel.basicPublish(
                    EXCHANGE_NAME,
                    severity,
                    null,
                    message.getBytes(StandardCharsets.UTF_8)
            );

            System.out.println(" [x] Sent '" + severity + "': '" + message + "'");
        }
    }
}

    mvn -q exec:java \
    -Dexec.mainClass="com.example.EmitLogDirect" \
    -Dexec.args="info Just an info log"

    mvn -q exec:java \
    -Dexec.mainClass="com.example.EmitLogDirect" \
    -Dexec.args="error Something went wrong"


  6. Consumer — ReceiveLogsDirect.java

    7. package com.example;

import com.rabbitmq.client.*;

import java.nio.charset.StandardCharsets;

public class ReceiveLogsDirect {

    private static final String EXCHANGE_NAME = "direct_logs";

    public static void main(String[] argv) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        // Declare direct exchange
        channel.exchangeDeclare(EXCHANGE_NAME, BuiltinExchangeType.DIRECT);

        // Create a fresh, exclusive, auto-delete queue
        String queueName = channel.queueDeclare().getQueue();

        if (argv.length < 1) {
            System.err.println("Usage: ReceiveLogsDirect [info] [warning] [error]");
            System.exit(1);
        }

        // Bind the queue for each severity given
        for (String severity : argv) {
            channel.queueBind(queueName, EXCHANGE_NAME, severity);
            System.out.println(" [*] Bound queue '" + queueName +
                               "' with routing key '" + severity + "'");
        }

        System.out.println(" [*] Waiting for logs. To exit press CTRL+C");

        // Define callback
        DeliverCallback deliverCallback = (consumerTag, delivery) -> {
            String routingKey = delivery.getEnvelope().getRoutingKey();
            String message = new String(delivery.getBody(), StandardCharsets.UTF_8);
            System.out.println(" [x] Received '" + routingKey + "': '" + message + "'");
        };

        CancelCallback cancelCallback = consumerTag -> {
            System.out.println(" [!] Consumer cancelled: " + consumerTag);
        };

        // Start consuming (autoAck = true is fine for simple log consumers)
        boolean autoAck = true;
        channel.basicConsume(queueName, autoAck, deliverCallback, cancelCallback);
    }
}


  7. Running Example Scenarios



  8. Routing vs Fanout vs Work Queues



  9. Extending the Routing Pattern



RabbitMQ — Streams in Java


  1. RabbitMQ Streams are an append-only log data structure built into RabbitMQ


  2. Prerequisites & Starting RabbitMQ with Streams


  3. Project Layout

    4. rabbitmq-stream-java/
├─ pom.xml
└─ src/
   └─ main/
      └─ java/
         └─ com/
            └─ example/
               ├─ StreamProducer.java
               └─ StreamConsumer.java


  4. Adding the RabbitMQ Stream Java Client Dependency

    5. <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>com.example</groupId>
    <artifactId>rabbitmq-stream-java</artifactId>
    <version>1.0.0</version>

    <dependencies>
        <dependency>
            <groupId>com.rabbitmq</groupId>
            <artifactId>stream-client</artifactId>
            <version>0.16.0</version> <!-- example version -->
        </dependency>
    </dependencies>
</project>
    mvn dependency:resolve


  5. Understanding the Stream Java Client Basics



  6. Producer — StreamProducer.java
    7. package com.example;

import com.rabbitmq.stream.Environment;
import com.rabbitmq.stream.Producer;
import com.rabbitmq.stream.Message;
import com.rabbitmq.stream.MessageBuilder;

public class StreamProducer {

    private static final String STREAM_NAME = "hello-stream";

    public static void main(String[] args) throws Exception {
        // 1. Create environment (connects to stream port 5552 by default in the URI)
        try (Environment environment = Environment.builder()
                .uri("rabbitmq-stream://localhost:5552")
                .build()) {

            // 2. Create the stream if it does not exist
            environment.streamCreator()
                    .stream(STREAM_NAME)
                    .create();

            // 3. Create a producer for that stream
            Producer producer = environment.producerBuilder()
                    .stream(STREAM_NAME)
                    .build();

            // 4. Build a simple message
            MessageBuilder messageBuilder = producer.messageBuilder();
            Message message = messageBuilder
                    .addData("Hello Stream from Java!".getBytes())
                    .build();

            // 5. Send the message (asynchronously)
            producer.send(message);

            System.out.println(" [x] Sent 'Hello Stream from Java!' to stream '" + STREAM_NAME + "'");

            // 6. Close producer explicitly
            producer.close();
        }
    }
}


  7. Consumer — StreamConsumer.java

    8. package com.example;

import com.rabbitmq.stream.Environment;
import com.rabbitmq.stream.Consumer;
import com.rabbitmq.stream.OffsetSpecification;
import com.rabbitmq.stream.MessageHandler;

import java.nio.charset.StandardCharsets;

public class StreamConsumer {

    private static final String STREAM_NAME = "hello-stream";

    public static void main(String[] args) throws Exception {
        Environment environment = Environment.builder()
                .uri("rabbitmq-stream://localhost:5552")
                .build();

        // Define how to handle messages
        MessageHandler handler = (context, message) -> {
            byte[] body = message.getBodyAsBinary();
            String text = new String(body, StandardCharsets.UTF_8);
            System.out.println(" [x] Received: " + text +
                               " (offset: " + context.getOffset() + ")");
        };

        // Start consumer from the beginning of the stream
        Consumer consumer = environment.consumerBuilder()
                .stream(STREAM_NAME)
                .offset(OffsetSpecification.first())
                .messageHandler(handler)
                .build();

        System.out.println(" [*] Consuming from stream '" + STREAM_NAME +
                           "' starting at the first message. Press CTRL+C to exit.");

        // Keep process alive (simple way)
        Thread.currentThread().join();

        // (Unreachable in this simple example, but good practice for structured shutdown)
        // consumer.close();
        // environment.close();
    }
}


  8. Building and Running the Example



  9. Streams vs Classic Queues