Sun Java System Message Queue 4.1 Developer's Guide for Java Clients

Message Header

Every message must have a header containing identifying and routing information. The header consists of a set of standard fields, which are defined in the Java Message Service Specification and summarized in Table 2–4. Some of these are set automatically by Message Queue in the course of producing and delivering a message, some depend on settings specified when a message producer sends a message, and others are set by the client on a message-by-message basis.

Table 2–4 Message Header Fields




Message identifier 


Destination to which message is sent 


Destination to which to reply 


Link to related message 


Delivery mode (persistent or nonpersistent) 


Priority level 


Time of transmission 


Expiration time 


Message type 


Has message been delivered before? 

The JMS Message interface defines methods for setting the value of each header field: for instance,


Table 2–5 lists all of the available header specification methods.

Table 2–5 Message Header Specification Methods




Set message identifier 


Set destination 


Set reply destination 


Set correlation identifier from string 


Set correlation identifier from byte array 


Set delivery mode 


Set priority level 


Set time stamp 


Set expiration time 


Set message type 


Set redelivered flag 

The message identifier (JMSMessageID) is a string value uniquely identifying the message, assigned and set by the message broker when the message is sent. Because generating an identifier for each message adds to both the size of the message and the overhead involved in sending it, and because some client applications may not use them, the JMS interface provides a way to suppress the generation of message identifiers, using the message producer method setDisableMessageID (see Sending Messages).

The JMSDestination header field holds a Destination object representing the destination to which the message is directed, set by the message broker when the message is sent. There is also a JMSReplyTo field that you can set to specify a destination to which reply messages should be directed. Clients sending such a reply message can set its JMSCorrelationID header field to refer to the message to which they are replying. Typically this field is set to the message identifier string of the message being replied to, but client applications are free to substitute their own correlation conventions instead, using either the setJMSCorrelationID method (if the field value is a string) or the more general setJMSCorrelationIDAsBytes (if it is not).

The delivery mode (JMSDeliveryMode) specifies whether the message broker should log the message to stable storage. There are two possible values, PERSISTENT and NON_PERSISTENT, both defined as static constants of the JMS interface DeliveryMode: for example,


The default delivery mode is PERSISTENT, represented by the static constant Message.DEFAULT_DELIVERY_MODE.

The choice of delivery mode represents a tradeoff between performance and reliability:

The message’s priority level (JMSPriority) is expressed as an integer from 0 (lowest) to 9 (highest). Priorities from 0 to 4 are considered gradations of normal priority, those from 5 to 9 of expedited priority. The default priority level is 4, represented by the static constant Message.DEFAULT_PRIORITY.

The Message Queue client runtime sets the JMSTimestamp header field to the time it delivers the message to the broker, expressed as a long integer in standard Java format (milliseconds since midnight, January 1, 1970 UTC). The message’s lifetime, specified when the message is sent, is added to this value and the result is stored in the JMSExpiration header field. (The default lifetime value of 0, represented by the static constant Message.DEFAULT_TIME_TO_LIVE, denotes an unlimited lifetime. In this case, the expiration time is also set to 0 to indicate that the message never expires.) As with the message identifier, client applications that do not use a message’s time stamp can improve performance by suppressing its generation with the message producer method setDisableMessageTimestamp (see Sending Messages).

The header field JMSType can contain an optional message type identifier string supplied by the client when the message is sent. This field is intended for use with other JMS providers; Message Queue clients can simply ignore it.

When a message already delivered must be delivered again because of a failure, the broker indicates this by setting the JMSRedelivered flag in the message header to true. This can happen, for instance, when a session is recovered or a transaction is rolled back. The receiving client can check this flag to avoid duplicate processing of the same message (such as when the message has already been successfully received but the client’s acknowledgment was missed by the broker).

See the Java Message Service Specification for a more detailed discussion of all message header fields.