JMS - Publish/Subscribe messaging example using ActiveMQ and Maven

In a publish/subscribe (pub/sub) product or application, clients address messages to a topic, which functions somewhat like a bulletin board. Subscribers can receive information, in the form of messages, from publishers. Topics retain messages only as long as it takes to distribute them to current subscribers. The following post introduces the basic concepts of JMS point-to-point messaging and illustrates them with a code sample using ActiveMQ and Maven.

Publish/Subscribe Messaging

Pub/sub messaging has the following characteristics:

• Each message can have multiple consumers.
• Publishers and subscribers have a timing dependency. A client that subscribes to a topic can consume only messages published after the client has created a subscription, and the subscriber must continue to be active in order for it to consume messages.

The JMS API relaxes this timing dependency mentioned in the second bullet to some extent by allowing subscribers to create durable subscriptions, which receive messages sent while the subscribers are not active. Durable subscriptions provide the flexibility and reliability of queues but still allow clients to send messages to many recipients.

ActiveMQ Example

Let's illustrate the above characteristics by creating a message producer that sends a message containing a first and last name to a topic. In turn a message consumer will read the message and transform it into a greeting. The code is very similar to the JMS Hello World example but contains a few key differences explained below.

Tools used:

• ActiveMQ 5.10
• Maven 3

<?xml version="1.0" encoding="UTF-8"?>
<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>info.source4code</groupId>
    <artifactId>easymock-powermock-facescontext</artifactId>
    <version>1.0</version>
    <packaging>jar</packaging>

    <name>EasyMock - Mocking FacesContext using PowerMock</name>
    <url>http://www.source4code.info/2014/11/easymock-mocking-facescontext-using.html</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.6</java.version>

        <junit.version>4.11</junit.version>
        <easymock.version>3.2</easymock.version>
        <powermock.version>1.5.6</powermock.version>

        <el.version>2.2.1-b04</el.version>
        <jsf.version>2.2.8-02</jsf.version>

        <maven-compiler-plugin.version>3.1</maven-compiler-plugin.version>
    </properties>

    <dependencies>
        <!-- JUnit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
        <!-- EasyMock -->
        <dependency>
            <groupId>org.easymock</groupId>
            <artifactId>easymock</artifactId>
            <version>${easymock.version}</version>
            <scope>test</scope>
        </dependency>
        <!-- PowerMock -->
        <dependency>
            <groupId>org.powermock</groupId>
            <artifactId>powermock-module-junit4</artifactId>
            <version>${powermock.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.powermock</groupId>
            <artifactId>powermock-api-easymock</artifactId>
            <version>${powermock.version}</version>
            <scope>test</scope>
        </dependency>
        <!-- EL (Unified Expression Language) -->
        <dependency>
            <groupId>javax.el</groupId>
            <artifactId>el-api</artifactId>
            <version>${el.version}</version>
            <scope>test</scope>
        </dependency>
        <!-- JSF -->
        <dependency>
            <groupId>com.sun.faces</groupId>
            <artifactId>jsf-api</artifactId>
            <version>${jsf.version}</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>${maven-compiler-plugin.version}</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

package info.source4code.jms.activemq.pubsub;

import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.JMSException;
import javax.jms.MessageProducer;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.Topic;

import org.apache.activemq.ActiveMQConnection;
import org.apache.activemq.ActiveMQConnectionFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Publisher {

    private static final Logger LOGGER = LoggerFactory
            .getLogger(Publisher.class);

    private String clientId;
    private Connection connection;
    private Session session;
    private MessageProducer messageProducer;

    @Test
    public void create(String clientId, String topicName) throws JMSException {
        this.clientId = clientId;

        // create a Connection Factory
        ConnectionFactory connectionFactory = new ActiveMQConnectionFactory(
                ActiveMQConnection.DEFAULT_BROKER_URL);

        // create a Connection
        connection = connectionFactory.createConnection();
        connection.setClientID(clientId);

        // create a Session
        session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

        // create the Topic to which messages will be sent
        Topic topic = session.createTopic(topicName);

        // create a MessageProducer for sending messages
        messageProducer = session.createProducer(topic);
    }

    public void closeConnection() throws JMSException {
        connection.close();
    }

    public void sendName(String firstName, String lastName) throws JMSException {
        String text = firstName + " " + lastName;

        // create a JMS TextMessage
        TextMessage textMessage = session.createTextMessage(text);

        // send the message to the topic destination
        messageProducer.send(textMessage);

        LOGGER.debug(clientId + ": sent message with text='{}'", text);
    }
}

If you would like to run the above code sample you can download the full source code and their corresponding JUnit test cases here.

This concludes the JMS publish/subscribe example using ActiveMQ. If you found this post helpful or have any questions or remarks, please leave a comment.