Sun Java System Message Queue 4.3 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.

When you create a consumer, you specify the destination from which it consumes messages.

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

These factors are described in the following sections.

Another factor that affects message delivery, the degree of reliability required by the messaging application, is described in Reliable Message Delivery.

In addition,Message Queue consumers can specify symbolic topic destination names that use wildcard characters. Messages are delivered to such wildcard consumers from all destinations that match the symbolic destination name. See Supported Topic Destination Names in Sun Java System Message Queue 4.3 Administration Guide.

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 (see Message 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

A durable subscriber is one for which the broker retains messages 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.