Newsletter sign-up

View all newsletters

Sign up for our technology specific newsletters.

Enterprise Java

Email Address:

Reflective XML-RPC

Dynamically invoke XML-based Remote Procedure Call

By Stephan Maier, JavaWorld.com, 02/07/05

XML-based Remote Procedure Call (XML-RPC) receives occasional attention as a simple protocol for remote procedure calls. It is straightforward to use, and easily available implementations such as Apache XML-RPC facilitate the protocol's use.

If your application is small or uses a limited number of remote procedures, you might prefer not to formally define the names of remote procedures and their signatures, but instead use XML-RPC in a straightforward way. Yet, if your application grows and the number of remote interfaces increases, you might find that the necessary conventions—remote methods and data objects—must be somehow fixed. In this article, I show how Java provides all you need to define remote interfaces and access remote methods: procedures and their signatures can be defined via Java interfaces, and remote procedure calls with XML-RPC can be wrapped such that both sides of a communication channel see only interfaces and suitable data objects.

This article also shows that when given Java interfaces describing the remote procedures and datastructures conforming to the JavaBeans specification, you can use the power of Java reflection as incorporated into the Reflection and JavaBeans packages to invoke remote methods transparently and convert between the data types of XML-RPC and Java with surprising ease.

Hiding complexity is good practice in itself. Needless to say, not all complexity can and should be hidden. With respect to distributed computing, this point has been famously made by Jim Waldo et al. in "A Note on Distributed Computing" (Sun Microsystems, November 1994). The framework presented here does not intend to hide the complexity of distributed computing, but it promises to reduce the pains involved in calling a remote procedure. For simplicity, I discuss only concurrent remote procedure calls and leave the asynchronous case to the zealous reader.

XML-RPC can be viewed as an oversimplification of RPC via SOAP. And by extension, the simple framework I discuss here must be regarded as a simplistic version of a SOAP engine, such as Axis. This article's main purpose is educational: I wish to show how reflection is employed to build a simple XML-RPC engine on top of existing XML-RPC frameworks. This may help you understand the inner workings of similar but vastly more complex engines for other protocols or how to apply reflection to solve different problems. A simple RPC engine can be used where a SOAP engine is clearly not feasible, such as with small applications that are not exposed via a Web server and where other forms of middleware are unavailable. Roy Miller's "XML-RPC in Java Programming" (developerWorks, January 2004) explains a useful example.

In this article, we use the Apache implementation of XML-RPC (Apache XML-RPC) to set up our framework. You do not need to know XML-RPC, nor do you need to understand the Apache XML-RPC framework, even though a basic understanding will help you appreciate what follows. This article focuses on the framework's precise inner workings, but does not make use of the protocol's details.

 

Improve efficiency with Visual Studio(r) 2010 Beta 2. - Microsoft

About Us | Advertise | Contact Us | Terms of Service/Privacy

Copyright, 2006-2008 Network World, Inc. All rights reserved.