2.7. Message Subject

A message has a subject property. This subject is used for message routing, and is synonomous with routing key.

Since the message subject is used for routing, it is not analogous to an email subject. In an email message the email address is used to route the email message to its recipient, and the email subject is available to describe the contents of the message. Since the message subject in a Qpid message is used to route a message, it is somewhat more like an email address, including the ability to send an email to one or multiple recipients with a single address.

A message's subject can be blank, it can be explicitly set manually, or it can be automatically set when the message is sent based on where it is to be routed.

Since the message subject can be automatically set when it is sent, you can develop applications where you never deal with the message subject, allowing it to be set by a sender. Or you can use a more generic sender, and set the subject of messages to influence their routing. A range of options are possible.

Suffice it to say that the subject of a message, whether set manually by you or automatically by a sender object, prescribes where the message will go.