3 MDBs and Messaging Models
These models are described in detail in Developing JMS Applications for Oracle WebLogic Server
This chapter includes the following sections:
Point-to-Point (Queue) Model: One Message Per Listener
Example: A department must update its back-end inventory system to reflect items sold throughout the day. Each message that decrements inventory must be processed once, and only once. It is not necessary for messages to be processed immediately upon generation or in any particular order, but it is critical that each message be processed.
Figure 3-1 illustrates a point-to-point application. Each message is processed by single instance of MDB_A. Message "M1" is processed by MDB_A(1), "M2" is processed by MDB_A(2), and "M3" is processed by MDB_A(3).
Figure 3-1 Point-to-Point Model
Description of "Figure 3-1 Point-to-Point Model"
Publish/Subscribe (Topic) Model
For stand-alone (non-distributed) topics, a logical subscription always consists of a single physical subscription on the topic. If an MDB goes down, that MDB will miss the message, unless the topic is a durable subscription topic. For information on durable subscriptions and for configuration instructions, see Setting Subscription Durability.
Example: A financial news service broadcasts stock prices and financial stories to subscribers, such as news wire services. Each message is distributed to each subscriber.
Figure 3-2 illustrates a publish/subscribe application. In contrast to a point-to-point application, in a publish/subscribe model, a copy of the message is processed for each of the logical subscriptions. In this diagram, there are two logical subscriptions, where each logical subscription consists of a separate physical subscription on the single topic. MDB_A has two instances that process the messages for a single dedicated subscription. Similarly, MDB_B has two instances that process the messages for a different single dedicated subscription. Message M1 is processed by an instance of MDB_A and an instance of MDB_B. Similarly, message M2 is processed by an instance of each of the subscribing MDBs.
Figure 3-2 Publish/Subscribe Model
Description of "Figure 3-2 Publish/Subscribe Model"
Potentially, a message can be processed more than once:
If an application fails, a transaction rolls back, or the hosting server instance fails during or after the
onMessage()method completes but before the message is acknowledged or committed, the message will be redelivered and processed again.
Non-persistent messages are also redelivered in the case of failure, except when the message's host JMS server shuts down or crashes, in which case the messages are destroyed.