Sun Java System Message Queue 3.7 UR1 Technical Overview

Consuming a Message

Messages are received by a message consumer, within the context of a connection and session. A client uses a message consumer object (MessageConsumer) to receive messages from a specified physical destination, represented in the API as a destination object.

Three factors affect how the broker delivers messages to a consumer:

The other major factor that affects message delivery and client design is the degree of reliability needed for the consumer. See Reliable Messaging.

Synchronous and Asynchronous Consumers

A message consumer can support either synchronous or asynchronous consumption of messages.

Using Selectors to Filter Messages

A message consumer can use a message selector to have the message service deliver only those messages whose properties match specific selection criteria. You specify this criteria when you create the consumer.

Selectors use an SQL-like syntax to match against message properties. For example,

color = ”red’
size > 10

Java clients can also specify selectors when browsing a queue; this allows you to see which selected messages are waiting to be consumed.

Using Durable Subscribers

You can use a session object to create a durable subscriber to a topic. The broker retains messages for these kinds of subscribers even when the subscriber becomes inactive.

Because the broker must maintain state for the subscriber and resume delivery of messages when the subscriber is reactivated, the broker must be able to identify a given subscriber throughout its comings and goings. The subscriber’s identity is constructed from the ClientID property of the connection that created it and the subscriber name specified when you create the subscriber.