Why do you want to create it in Java? You can just use a map step to create it.
Using Java comes to my mind only if I need to publish from Java code (which I usually do not need to do inside IS), in this case you can use the Broker Java API (documented in x-x_Broker_Java_Client_Programmers_Guide.pdf and x-x_Broker_Java_Client_API_Reference).
#webMethods#Integration-Server-and-ESB