Working with Web Services - Beginning Java 7 - page 1030

Figure 11-4. A SOAP-based web service involves a service requester, a service provider, and a
service broker (UDDI, for example).
Theservicerequester,typicallyaclientapplication(e.g.,awebbrowser),orperhaps
anotherwebservice,firstlocatestheserviceproviderinsomemanner.Forexample,the
service requester might send a WSDL document to a service broker, which responds
with another WSDL document identifying the service provider's location. The service
requester then communicates with the service provider via SOAP messages.
Service providers need to be published so that others can locate and use them. In
August 2000, an open industry initiative known as Universal Description, Discovery,
and Integration (UDDI)waslaunchedtoletbusinessespublishservicelistings,discover
eachother,anddefinehowtheservicesorsoftwareapplicationsinteractovertheInter-
net. However, this platform-independent, XML-based registry was not widely adopted
and currently isn't used. Many developers found UDDI to be overly complicated and
lacking in functionality, and opted for alternatives such as publishing the information
onawebsite. Forexample, Googlemakes itspublic webservices (e.g.,GoogleMaps)
available through its http://code.google.com/more/ website.
The SOAP messages that flow between service requesters and service providers
are often unseen, being passed as requests and responses between the SOAP libraries
of their web service protocol stacks (see http://en.wikipedia.org/wiki/
Web_services_protocol_stack ). However, it's possible to access these mes-
sages directly, as you will discover later in this chapter.