Red Hat Application Server, Руководство пользователя

Страница: 128 / 296

120 Chapter 9. Developing Message-Driven Beans
public class MdbBean implements MessageDrivenBean, MessageListener {
private transient MessageDrivenContext mdbContext;
public MdbBean() {}
public void setMessageDrivenContext(MessageDrivenContext ctx) {
mdbContext = ctx;
}
public void ejbRemove() {}
public void ejbCreate() {}
public void onMessage(Message message) {
try {
TextMessage mess = (TextMessage)message;
System.out.println( "Message received: "+mess.getText());
}catch(JMSException ex){
System.err.println("Exception caught: "+ex);
}
}
}
The destination associated with an MDB is specified in the deployment descriptor of the bean. A des-
tination is a JMS-administered object, accessible via JNDI (the Java Naming and Directory Interface).
The description of an MDB in the EJB 2.1 deployment descriptor contains the following elements,
which are specific to MDBs:
•
The JMS acknowledgement mode: auto-acknowledge or dups-ok-acknowledge (refer to the JMS
specification for the definition of these modes)
•
An eventual JMS message selector: this is a JMS concept which allows the filtering of the messages
sent to the destination
•
A message-driven-destination, which contains the destination type (Queue or Topic) and the sub-
scription durability (in the case of Topic)
The following example illustrates such a deployment descriptor:
r
enterprise-beans
s
r
message-driven
s
r
description
s
Describe here the message driven bean Mdb
r
/description
s
r
display-name
s
Message Driven Bean Mdb
r
/display-name
s
r
ejb-name
s
Mdb
r
/ejb-name
s
r
ejb-class
s
samplemdb.MdbBean
r
/ejb-class
s
r
transaction-type
s
Container
r
/transaction-type
s
r
message-selector
s
Weight
s
= 60.00 AND LName
LIKE ’Sm_th’
r
/message-selector
s
r
message-driven-destination
s
r
destination-type
s
javax.jms.Topic
r
/destination-type
s
r
subscription-durability
s
NonDurable
r
/subscription-durability
s
r
/message-driven-destination
s
r
acknowledge-mode
s
Auto-acknowledge
r
/acknowledge-mode
s
r
/message-driven
s
r
/enterprise-beans
s
If the transaction type is “container,” the transactional behavior of the MDB’s methods are defined as
for other enterprise beans in the deployment descriptor, as in the following example:
r
assembly-descriptor
s