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.