Java and XML, Second Edition

Getting Dirty

There are three basic steps in writing any SOAP-based system, and I’ll look at each in turn:

• Decide on SOAP-RPC or SOAP messaging

• Write or obtain access to a SOAP service

• Write or obtain access to a SOAP client

The first step is to decide if you want to use SOAP for RPC-style calls, in which a remote procedure is invoked on a server, or for messaging, in which a client simply sends pieces of information to a server. I’ll detail these processes in the next section. Once you’ve made that design decision, you need to access, or code up, a service. Of course, since we’re all Java pros here, this chapter shows you how to code up your own. Finally, you need to write the client for this service, and watch things take off.

RPC or Messaging?

Your first task is actually not code-related but design-related. You need to determine if you want an RPC service or a messaging one. The first, RPC, is something you should be pretty familiar with after the last chapter. A client invokes a remote procedure on a server somewhere, and then gets some sort of response. In this scenario, SOAP is simply acting as a more extensible XML-RPC system, allowing better error handling and passing of complex types across the network. This is a concept you should already understand, and because it turns out that RPC systems are simple to write in SOAP, I’ll start off there. This chapter describes how to write an RPC service, and then an RPC client, and put the system in action.

The second style of SOAP processing ...