Pass message payload by reference: Usage scenarios and example code for forwarding applications

A JMS forwarder application receives a message (through a connection factory, or if it is a message-driven bean through an activation specification), then sends the message object on to another destination. Explore the different usage scenarios, then code your JMS forwarding applications so that you can safely pass message payloads by reference when forwarding messages from one queue to another within a single server.

When large object messages or bytes messages are sent, the cost in memory and processor use of serializing, deserializing, and copying the message payload can be significant. If you enable the pass message payload by reference properties on a connection factory or activation specification, you tell the default messaging provider to override the JMS 1.1 specification and potentially reduce or bypass this data copying.

In the following figure, messages pass from queue1 on a messaging engine, through a consumer activation specification or connection factory, to a JMS forwarding application. They are then forwarded through a producer connection factory to queue2 on the same messaging engine.

CAUTION:

The parts of the JMS Specification that are bypassed by these properties are defined to ensure message data integrity. Any of your JMS applications that use these properties must strictly follow the rules that are described or you risk losing data integrity.

The figure illustrates the flow of messages from one queue to another. From queue1, the messages pass to the JMS forwarding application through the consumer activation specification or connection factory property. From the JMS forwarding application, the messages are then forwarded to queue2 through the producer connection factory property. — Figure 1. Forwarding messages

To understand the usage scenarios and associated example code given in this topic, you must note these important characteristics of a JMS forwarding application:

A forwarding application does not replace the message object. This is useful if your application is just logging or otherwise recording (for example, printing out) the message before forwarding it, and also means that the forwarded message retains some useful message properties such as the JMSCorrelationID, JMSReplyTo and JMSType properties.
A forwarding application can modify or replace the message payload. If it replaces the payload, it sets the new payload in the message object and changes the payload reference to point to the new message payload.
For a forwarding application, the forwarded message is created and configured by the consumer connection factory or activation specification. The producer connection factory is used solely to route the forwarded message and has no effect upon the contents of the forwarded message.

The following table describes the four forwarding application usage scenarios that affect how you set the pass message payload by reference properties. Note that, because the producer connection factory has no effect upon the contents of the forwarded message, you set both the consumer properties and the producer/forwarder properties on the consumer connection factory or activation specification.

Table 1. Effect of the pass message payload by reference property settings on the forwarding application usage scenarios . The first column of the table lists the four forwarding application usage scenarios. The second column indicates the consumer property setting for the scenarios. The third column indicates the connection or the activation specification property setting for the scenarios.
Forwarding application usage scenario	consumerDoesNotModify PayloadAfterGet property setting	producerDoesNotModify PayloadAfterSet (for connection factories) or forwarderDoesNotModify PayloadAfterSet (for activation specifications) property setting
Scenario 1: The application receives a message, looks at the payload but does not modify it, and forwards the message on without modifying or replacing the payload.	Enabled	Not required, but can be enabled
Scenario 2: The application receives a message, looks at the payload but does not modify it, replaces the payload in the message with a new payload and forwards the message on without modifying the payload after the call to set it into the message.	Enabled	Enabled
Scenario 3: The application receives a message, looks at and modifies the payload, then sets the modified payload or some other data back into the message and forwards the message on without further modifying the payload after the call to set it into the message.	NOT enabled	Enabled
Scenario 4: The application receives a message, looks at and modifies the payload, then sets the modified payload or some other data back into the message, then further modifies the payload after the call to set it into the message.	NOT enabled	NOT enabled

For scenarios 1, 2 and 3 you can enable one or more of the pass message payload by reference properties, provided that your forwarding application can guarantee to behave as described in the scenario. To help you achieve this, here is some example code that you can adapt for use in your applications.

Forwarding application: scenario 1

The application receives a message, looks at the payload but does not modify it, and forwards the message on without modifying or replacing the payload.

public void onMessage (Message message)
{
   ObjectMessage oMessage = (ObjectMessage) message;
   DataObject data = oMessage.getObject();
   System.out.print(data.getXXX());
   System.out.print(data.getYYY());

   // get a session to forward on the received message
   
   producer.send(message);
   session.close();
}

Forwarding application: scenario 2

The application receives a message, looks at the payload but does not modify it, replaces the payload in the message with a new payload and forwards the message on without modifying the payload after the call to set it into the message.

public void onMessage (Message message)
{
   ObjectMessage oMessage = (ObjectMessage) message;
   DataObject data = oMessage.getObject();
   System.out.print(data.getXXX());
   System.out.print(data.getYYY());

   // get a session to forward on the received message
   
   message.setObject(newData);

   producer.send(message);
   session.close();
}

For bytes messages, your application must also guarantee to write only a single full byte array into the message.

byte [] data = myByteData; 
BytesMessage message = session.createBytesMessage(); 
message.writeBytes(data); 
data = null;	 
producer.send(message);

Forwarding application: scenario 3

The application receives a message, looks at and modifies the payload, then sets the modified payload or some other data back into the message and forwards the message on without further modifying the payload after the call to set it into the message.

public void onMessage (Message message)
{
   ObjectMessage oMessage = (ObjectMessage) message;
   DataObject data = oMessage.getObject();
   System.out.print(data.getXXX());
   System.out.print(data.getYYY());

   // get a session to forward on the received message

   data.setXXX(xxx);
   data.setYYY(yyy);
   message.setObject(data);

   producer.send(message);
   session.close();
}

For bytes messages, your application must also guarantee to write only a single full byte array into the message.

byte [] data = myByteData; 
BytesMessage message = session.createBytesMessage(); 
message.writeBytes(data); 
data = null;	 
producer.send(message);