Patterns: Implementing Self-Service in an SOA Environment

208 Patterns: Implementing Self-Service in an SOA Environment

Each listener monitors either a JMS queue destination for point-to-point

messaging, or a JMS topic destination for publish/subscribe messaging.

A connection factory is used to create connections with the JMS provider for a

specific JMS queue or topic destination. Each connection factory encapsulates

the configuration parameters needed to create a connection to a JMS

destination.

A listener port defines the association between a connection factory, a

destination, and a deployed message-driven bean. Listener ports are used to

simplify the administration of the associations between these resources.

When a deployed message-driven bean is installed, it is associated with a

listener port and the listener for a destination. When a message arrives on the

destination, the listener passes the message to a new instance of a

message-driven bean for processing.

When an application server is started, it initializes the listener manager based on

the configuration data. The listener manager creates a dynamic session thread

pool for use by listeners, creates and starts listeners, and during server

termination controls the cleanup of listener message service resources. Each

listener completes several steps for the JMS destination that it is to monitor,

including:

򐂰 Creating a JMS server session pool, and allocating JMS server sessions and

session threads for incoming messages.

򐂰 Interfacing with JMS ASF to create JMS connection consumers to listen for

incoming messages.

򐂰 If specified, starting a transaction and requesting that it is committed (or rolled

back) when the EJB method has completed.

򐂰 Processing incoming messages by invoking the onMessage() method of the

specified enterprise bean.

7.5.4 Managing JMS objects

JMS Connection is the first point of access to JMS objects. JMS Connection is

created from JMS ConnectionFactory. Once a connection is created, one or

more sessions can be created in the context of the connection. JMS Sessions

allow you to create message consumers and producers. When consumers or

producers are created, the connection needs to be started to receive or send

messages. JMS Connections can be cached, similar to the way EJB home

objects are cached, and reused by many clients.

JMS Sessions are designed for synchronous access only. A session can only be

used by a single client and not shared among other clients. Similarly, an instance