Solutions in this chapter:

• JAX-RPC Summary

• Mapping Java Data Types

• Conversion Between Java Classes and WSDL

• Creating a JAX-RPC Client

• Creating a JAX-RPC Server

• Creating a Simple XML-RPC Server and Client

Introduction

You might think that the last thing the world needs is another remote procedure call protocol; after all, there are dozens already in existence. That s largely a true statement, and for many situations, XML-based RPC offers few advantages over existing remote procedure call interfaces. Further, encoding the request into XML makes the calls less efficient than direct (binary) interfaces.

However, there are times when XML-based RPC solves a business problem. You might have to communicate via an RPC mechanism across organizational boundaries through firewalls, for instance. Alternately, you might be communicating with wildly disparate systems a mainframe speaking PL/1 and a desktop speaking Java. You might even be creating a server system where you have no way of knowing the remote client, let alone controlling it. XML-based RPC also provides some resilience in the face of change. Since the published interfaces are XML-based instead of binary, elements can sometimes be added or removed without breaking the connection between the server and existing clients.

JAX-RPC uses two industry standards surrounding XML-based RPC: SOAP and WSDL. SOAP (covered in chapters 6 & 7) is used for the transfer of data between end points. Web Service Description Language (WSDL) is the functional analog of IDL files in other remote procedure systems: it provides a common language for describing the inputs, outputs and...