A user-defined parser is a program that interprets the bit stream of an incoming message and creates an internal representation of the message in a tree structure. A user-defined parser can also regenerate a bit stream for an outgoing message from the internal message tree representation
In addition to the parsers provided by WebSphere® Message Broker, you can provide alternative and complementary message parsers that are accessible to the broker and its message processing nodes through a standard set of parsing and construction interfaces.
If you need to process messages that do not conform to any of the defined message domains you can use the C language programming interface to create a user-defined parser.