NonStop JMS User's Manual (H06.03+, J06.03+, NonStop JMS 3.0+)

NSJMS and JMS Client Applications

NonStop Server for Java Message Service User’s Manual—522356-006

4-9

Priority

JMS allows message priority to be set by the setPriority() method on the

MessageProducer object and retrieved using the getPriority() method on the

MessageConsumer object. Although NSJMS allows message priority to be set and

retrieved, this priority does not affect message-delivery order.

Receiving Messages

A JMS client uses a MessageConsumer to receive messages from a specified

destination. A message consumer is an object created by a session that is used by

JMS clients to receive messages from queues or topics. The PTP messaging

application uses QueueReceiver as its message consumer, and the Pub/Sub

messaging application uses TopicSubscriber as its message consumer.

Receiving Messages from a Queue

To receive a message from a queue, you create a QueueReceiver using the

createReceiver() method. This method uses a Queue parameter to define where

the messages are received from. This code fragment receives a message from a

queue and then reads back the message:

QueueReceiver receiver = session.createReceiver(queue);

Message message = receiver.receive();

The receive() method without parameters blocks indefinitely unless a timeout

parameter is specified. When specified, this parameter defines how long the

receive() method should wait when no messages are available. No delay occurs if

the receiveNoWait() method is used.

The receive() method returns a message of the same type as was sent to the

queue. For example, if a StreamMessage is sent to a queue, the receive() method

returns an object of type StreamMessage.

To pull the content from the body of the message, you must identify the subclass of the

message contents, such as TextMessage. If you do not know the message-contents

subclass, use instanceof to determine if the contents of a message are of a certain

type. It is good practice always to test the message class before casting, so that

unexpected errors are handled gracefully.