To call a Web service, several pieces of information are required. In particular, the location (URL) of the service and the schema to pass requests in are critical for a message to be understood by the right remote service.

The simplest means of deriving this information is by hand. You can, for instance, communicate with a fellow programmer or use Web sites such as www.xmethods.com to find out the relevant information. However, the problem with this method is that with the Web being a fluid environment, new services are added and old ones removed continually. Consequently, evaluating the connection protocol for a Web service by hand calls for a lot of maintenance work to ensure the system continues to run smoothly.

To solve this problem, Web services can be published to registries. A registry is a collection of meta-information about Web services such as their location, the protocol used to contact them and so forth. While registries were originally seen as a global mechanism where companies published Web services for anonymous business partners to find more commonly, registries are being used internally by organizations to render service-based architectures more resilient and reliable.

In this chapter, we will explore JAXR, the Web Services Developer Pack component employed for communicating with registries. Additionally, we will introduce WSDL, the standard mechanism for describing the schema with which to call a remote service.