Patterns: Implementing Self-Service in an SOA Environment

Chapter 7. Application and system design guidelines 209

of either MessageConsumer and MessageProducer can only be used by a single

client. JMS Sessions are opened for the duration of message sending or

receiving; after this the session can be closed.

When a session is opened, the correct session acknowledgment must be

selected from a performance perspective. In our sample scenario, we selected

AUTO_ACKNOWLEDGE. This policy specifies that the message be delivered

once and only once. The server must send an acknowledgment back, so the

server incurs an overhead to implement this policy. The

DUPS_OK_ACKNOWLEDGE setting resends the message until an

acknowledgment is sent from the server. The server will operate in a lazy

acknowledge mode, thereby reducing the overhead on the server but resulting in

an increase in network traffic. With the most overhead of the three settings,

CLIENT_ACKNOWLEDGE will cause the server to wait until a request for

acknowledgment is sent from the client. Usually the client calls the sent

message’s acknowledge method.

On completion of interaction with the message producer or consumer (sender or

receiver), the session needs to be closed. If the connection is closed, the session

belonging to this connection is automatically closed.

The message producers and consumers must also be closed when you finish

sending and receiving messages. Again if the connection is closed, the

producers and consumers are automatically closed.

Garbage collection of Java cannot be relied upon to clean out objects in a timely

manner. It is always a good practice to call the close of any resource-bound

object.

For further information, read the JMS specification at:

http://java.sun.com/products/jms/docs.html

7.5.5 JMS and JNDI

The Java Naming and Directory Interface (JNDI) API implementation provides

directory and naming functionality to programs developed in Java. This allows

Java programs to discover and retrieve objects of any type from the JNDI name

space.

JMS has two types of administered objects:

򐂰 ConnectionFactory

򐂰 Destination

An administrator can place objects of these types in the JNDI name space to be

accessed by messaging applications.