5.13. Message Driven Beans
A message-driven bean is an enterprise bean that allows J2EE applications to process messages asynchronously. It acts as a JMS message listener, which is similar to an event listener except that it receives messages instead of events. The messages may be sent by any J2EE component--an application client, another enterprise bean, or a Web component--or by a JMS application or system that does not use J2EE technology. This definition is from http://java.sun.com/j2ee/tutorial/1_3-fcs/doc/EJBConcepts5.html , and you can read more about message driven beans (MDB) from there.
You can specify MDBs in a deployment descriptor or using annotations.
- Using a descriptor
<enterprise-beans> <message-driven> <ejb-name>MDBExample</ejb-name> <destination-jndi-name>queue/@QUEUE_NAME@</destination-jndi-name> </message-driven> </enterprise-beans>
- Using an annotation
@MessageDriven(mappedName="jms/Queue") public class SimpleMessageBean implements MessageListener { @Resource private MessageDrivenContext mdc; ...
You configure MDBs using properties divided into those specified by the JCA specification, and those available as JBoss extensions.
Important
MDB properties listed in Table 5.1, “MDB Properties Provided by the JCA Specification” are not mandatory, unless explicitly called out in the Remarks column.
Table 5.1. MDB Properties Provided by the JCA Specification
Name | Type | Default value | Remarks |
---|---|---|---|
destination | java.lang.String | none |
This property is Mandatory
The JNDI name of the Queue or Topic.
|
destinationType | java.lang.String | none |
The type of destination valid values are javax.jms.Queue or javax.jms.Topic
|
messageSelector | java.lang.String | none |
The message selector of the subscription
|
acknowledgeMode | int | AUTO_ ACKNOWLEDGE |
The type of acknowledgement when not using transacted jms - valid values AUTO_ ACKNOWLEDGE or DUPS_OK_ ACKNOWLEDGE
|
clientID | java.lang.String |
The client id of the connection
| |
subscriptionDurability | String | NonDurable |
Whether topic subscriptions are durable. Valid values are Durable or NonDurable
|
subscriptionName | String | none |
The subscription name of the topic subscription
|
Important
MDB properties listed in Table 5.2, “MDB Properties Provided as JBoss Extensions” are not mandatory, unless explicitly called out in the Remarks column.
Table 5.2. MDB Properties Provided as JBoss Extensions
Name | Type | Default value | Remarks |
---|---|---|---|
isTopic | boolean | false |
Sets the destinationType
|
providerAdapterJNDI | java.lang.String | DefaultJMSProvider | The JNDI name of the JMS provider. |
user | java.lang.String | none | The user ID used to connect to the JMS server |
pass | java.lang.String | none | The password of the user |
maxMessages | int | 1 |
Read this number of messages before delivering messages to the MDB.
Each message is delivered individually on the same thread in an attempt to avoid context excessive context switching
|
minSession | int | 1 | The minimum number of JMS sessions that are available to concurrently deliver messages to this mdb |
maxSession | int | 15 | The maximum number of JMS sessions that are available to concurrently deliver messages to this mdb |
reconnectInterval | long | 10 seconds | The length of time in seconds between attempts to (re-)connect to the JMS provider |
keepAlive | long | 60 seconds | The length of time in milliseconds that sessions over the minimum are kept alive |
sessionTransacted | boolean | true | Whether the sessions are transacted |
useDLQ | boolean | true | Whether to use a Dead Letter Queue (DLQ) handler. |
dLQJNDIName | java.lang.String | queue/DLQ | The JNDI name of the DLQ |
dLQHandler | java.lang.String |
org.jboss.resource. adapter.jms.inflow.dlq. GenericDLQHandler
| The org.jboss.resource. adapter.jms.inflow. DLQHandler implementation class name. |
dLQUser | java.lang.String | none | The user id used to make the dlq connection to the JMS server |
dLQPassword | java.lang.String | none | The password of the dLQUser |
dLQClientID | java.lang.String | none | The client id of the DLQ connection |
dLQMaxResent | int | 5 | The maximum number of times a message is redelivered before it is sent to the DLQ. |
redeliverUnspecified | boolean | true | Whether to attempt to redeliver a message in an unspecified transaction context |
transactionTimeout | int | Default is the timeout set for the resource manager | Time in seconds for the transaction timeout |
DeliveryActive | boolean | true | Whether the MDB should make the subscription at initial deployment or wait for start() or stopDelivery() on the corresponding MBean. You can set this to false if you want to prevent messages from being delivered to the MDB (which is still starting) during server start up. |
Configuring default MDB properties
You can configure MDBs to have default properties using the @org.jboss.ejb3.annotation.DefaultActivationSpecs
annotations.