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Chapter 2. Connecting to a Broker
Abstract
The Red Hat JBoss A-MQ client APIs follow the standard JMS pattern.
Regardless of the API in use, the pattern for establishing a connection between a messaging client and a message broker is the same. You must:
- Get an instance of the Red Hat JBoss A-MQ connection factory.Depending on the environment, the application can create a new instance of the connection factory or use JNDI, or another mechanism, to look up the connection factory.
- Use the connection factory to create a connection.
- Get an instance of the destination used for sending or receiving messages.Destinations are administered objects that are typically created by the broker. The JBoss A-MQ allows clients to create destinations on-demand. You can also look up destinations using JNDI or another mechanism.
- Use the connection to create a session.The session is the factory for creating producers and consumers. The session also is a factory for creating messages.
- Use the session to create the message consumer or message producer.
- Start the connection.
Note
You can add configuration information when creating connections and destinations.
2.1. Connecting with the Java API
Overview
Red Hat JBoss A-MQ clients use the standard JMS APIs to interact with the message broker. Most of the configuration properties can be set using the connection URI and the destination specification used.
Developers can also use the JBoss A-MQ specific implementations to access JBoss A-MQ configuration features. Using these APIs will make your client non-portable.
The connection factory
The connection factory is an administered object that is created by the broker and used by clients wanting to connect to the broker. Each JMS provider is responsible for providing an implementation of the connection factory and the connection factory is stored in JNDI and retrieved by clients using a JNDI lookup.
The JBoss A-MQ connection factory,
ActiveMQConnectionFactory, is used to create connections to brokers and does not need to be looked up using JNDI. Instances are created using a broker URI that specifies one of the transport connectors configured on a broker and the connection factory will do the heavy lifting.
Example 2.1, “Connection Factory Constructors” shows the syntax for the available
ActiveMQConnectionFactory constructors.
Example 2.1. Connection Factory Constructors
ActiveMQConnectionFactory(String brokerURI);ActiveMQConnectionFactory(URI brokerURI);ActiveMQConnectionFactory(String username,
String password,
String brokerURI);ActiveMQConnectionFactory(String username,
String password,
URI brokerURI);
The broker URI also specifies connection configuration information. For details on how to construct a broker URI see the Connection Reference.
The connection
The connection object is created from the connection factory and is the object responsible for maintaining the link between the client and the broker. The connection object is used to create session objects that manage the resources used by message producers and message consumers.
For more applications the standard JMS
Connection object will suffice. However, JBoss A-MQ does provide an implementation, ActiveMQConnection, that provides a number of additional methods for working with the broker. Using ActiveMQConnection will make your client code less portable between JMS providers.
The session
The session object is responsible for managing the resources for the message consumers and message producers implemented by a client. It is created from the connection, and is used to create message consumers, message producers, messages, and other objects involved in sending and receiving messages from a broker.
Example
Example 2.2, “JMS Producer Connection” shows code for creating a message producer that sends messages to the queue
EXAMPLE.FOO.
Example 2.2. JMS Producer Connection
import org.apache.activemq.ActiveMQConnectionFactory;
import javax.jms.Connection;
import javax.jms.DeliveryMode;
import javax.jms.Destination;
import javax.jms.ExceptionListener;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageConsumer;
import javax.jms.MessageProducer;
import javax.jms.Session;
import javax.jms.TextMessage;
...
// Create a ConnectionFactory
ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory("tcp://localhost:61616");
// Create a Connection
Connection connection = connectionFactory.createConnection();
// Create a Session
Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
// Create the destination
Destination destination = session.createQueue("EXAMPLE.FOO");
// Create a MessageProducer from the Session to the Queue
MessageProducer producer = session.createProducer(destination);
// Start the connection
connection.start();