Learning Java, 4th Edition

Web Services

Web services is a big, fast-moving topic and the subject of many other fine O’Reilly books. However, because we have already covered so many of the basic networking concepts (and we’ll cover XML in detail in Chapter 24), we would be shirking our duties if we didn’t provide an introduction to this important area of application development. We conclude this chapter on client-side web communications with a small example of invoking a web service.

In contrast to regular web applications intended to be visited by web browsers, web services are application-level APIs intended to be invoked by other application components. The primary distinction from other types of interapplication communications mechanisms is that they use web standards and XML to maximize cross-platform interoperability. We will leave the analysis of when exactly this is important and the cost versus benefits tradeoffs out of our discussion here. But the value in this idea should be evident from the explosion of web-based business applications in the past few years. Web services allow web-based applications to provide well-defined, cross-platform interfaces for other web-based applications.

XML-RPC

The term web services means different things to different people and has spawned many (too many) new standards in recent years. In fact, there are so many web service standards named with the prefix “WS” now that they are collectively known as “WS-*” (affectionately referred to as WS “splat” or WS “death star”). ...