Java Reference
In-Depth Information
• A language used to define the interfaces provided by a web service in a
manner that is not dependent on the platform on which it is running or the
programming language used to implement it
• A common standard format for exchanging messages between web ser-
vice
providers
and web service
consumers
• A registry within which service definitions can be placed
The
Web Service Description Language
, also known as WSDL, (
ht-
tp://www.w3.org/TR/wsdl
) is the de facto standard for providing a description of a
web service contract exposed to clients. In particular, a WSDL document describes a
web service in terms of the operations that it provides, and the data types that each
operation requires as inputs and can return in the form of results.
Communication between the service provider and service consumer happens by
means of XML messages that rely on the
SOAP
specification.
A basic SOAP message consists of an envelope that may contain any number of
headers and a body. These parts are delimited by XML elements called
envelope
,
header
, and
body
that belong to a namespace defined by the SOAP specification.
The following figure depicts the basic structure of a SOAP message:
Strategies for building SOAP web services
As we have just learned, the service description is provided by a commonly-used
document interface named
WSDL
that exposes the services as a collection of net-
works, endpoints, and ports, using the XML format.
You may logically be inclined to think that it is necessary to state the corresponding
programming interfaces at the beginning of the contract of the service and then pro-
duce them.
Actually, you can follow two approaches for developing your SOAP web services:
