java WebService

In recent years, web services have emerged as a popular technology for remote method calls. Technically, a web service has two components:
A service that can be accessed with the SOAP transport protocol
A description of the service in the WSDL format
SOAP is an XML protocol for invoking remote methods, similar to the protocol that RMI uses for the communication between clients and servers. Just as you can program RMI applications without knowing anything about the details of the RMI protocol, you don't really need to know any details about SOAP to call a web service.
WSDL is an interface description language. It too is based on XML. A WSDL document describes the interface of a web service: the methods that can be called, and their parameter and return types. In this section, we generate a WSDL document from a service implemented in Java. This document contains all the information that a client program needs to invoke the service, whether it is written in Java or another programming language.