Java Platform, Enterprise Edition (Java EE) 8
The Java EE Tutorial
A message-driven bean is an enterprise bean that allows Java EE applications to process messages asynchronously. This type of bean normally acts as a JMS message listener, which is similar to an event listener but receives JMS messages instead of events. The messages can be sent by any Java EE component (an application client, another enterprise bean, or a web component) or by a JMS application or system that does not use Java EE technology. Message-driven beans can process JMS messages or other kinds of messages.
The following topics are addressed here:
The most visible difference between message-driven beans and session beans is that clients do not access message-driven beans through interfaces. Interfaces are described in the section Accessing Enterprise Beans. Unlike a session bean, a message-driven bean has only a bean class.
In several respects, a message-driven bean resembles a stateless session bean.
A message-driven bean’s instances retain no data or conversational state for a specific client.
All instances of a message-driven bean are equivalent, allowing the EJB container to assign a message to any message-driven bean instance. The container can pool these instances to allow streams of messages to be processed concurrently.
A single message-driven bean can process messages from multiple clients.
The instance variables of the message-driven bean instance can contain some state across the handling of client messages, such as a JMS API connection, an open database connection, or an object reference to an enterprise bean object.
Client components do not locate message-driven beans and invoke methods
directly on them. Instead, a client accesses a message-driven bean
through, for example, JMS by sending messages to the message destination
for which the message-driven bean class is the
assign a message-driven bean’s destination during deployment by using
GlassFish Server resources.
Message-driven beans have the following characteristics.
They execute upon receipt of a single client message.
They are invoked asynchronously.
They are relatively short-lived.
They do not represent directly shared data in the database, but they can access and update this data.
They can be transaction-aware.
They are stateless.
When a message arrives, the container calls the message-driven bean’s
onMessage method to process the message. The
normally casts the message to one of the five JMS message types and
handles it in accordance with the application’s business logic. The
onMessage method can call helper methods or can invoke a session bean
to process the information in the message or to store it in a database.
A message can be delivered to a message-driven bean within a transaction
context, so all operations within the
onMessage method are part of a
single transaction. If message processing is rolled back, the message
will be redelivered. For more information, see
Receiving Messages Asynchronously Using a
Message-Driven Bean and Chapter 54,
Session beans allow you to send JMS messages and to receive them synchronously but not asynchronously. To avoid tying up server resources, do not to use blocking synchronous receives in a server-side component; in general, JMS messages should not be sent or received synchronously. To receive messages asynchronously, use a message-driven bean.