Web services are web-based enterprise applications that use open, XML-based standards and transport protocols to exchange data with calling clients. The Java EE platform provides the XML APIs and tools you need to quickly design, develop, test, and deploy web services and clients that fully interoperate with other web services and clients running on Java-based or non-Java-based platforms.
To write web services and clients with the Java EE XML APIs, all you need to do is pass parameter data to the method calls and process the data returned; for document-oriented web services, you send documents containing the service data back and forth. No low-level programming is needed because the XML API implementations do the work of translating the application data to and from an XML-based data stream that is sent over the standardized XML-based transport protocols. These XML-based standards and protocols are introduced in the following sections.
The translation of data to a standardized XML-based data stream is what makes web services and clients written with the Java EE XML APIs fully interoperable. This does not necessarily mean that the data being transported includes XML tags, because the transported data can itself be plain text, XML data, or any kind of binary data, such as audio, video, maps, program files, computer-aided design (CAD) documents, and the like. The next section introduces XML and explains how parties doing business can use XML tags and schemas to exchange data in a meaningful way.
Extensible Markup Language (XML) is a cross-platform, extensible, text-based standard for representing data. Parties that exchange XML data can create their own tags to describe the data, set up schemas to specify which tags can be used in a particular kind of XML document, and use XML style sheets to manage the display and handling of the data.
For example, a web service can use XML and a schema to produce price lists, and companies that receive the price lists and schema can have their own style sheets to handle the data in a way that best suits their needs. Here are examples.
One company might put XML pricing information through a program to translate the XML into HTML so that it can post the price lists to its intranet.
A partner company might put the XML pricing information through a tool to create a marketing presentation.
Another company might read the XML pricing information into an application for processing.
Client requests and web service responses are transmitted as Simple Object Access Protocol (SOAP) messages over HTTP to enable a completely interoperable exchange between clients and web services, all running on different platforms and at various locations on the Internet. HTTP is a familiar request-and-response standard for sending messages over the Internet, and SOAP is an XML-based protocol that follows the HTTP request-and-response model.
The SOAP portion of a transported message does the following:
Defines an XML-based envelope to describe what is in the message and explain how to process the message
Includes XML-based encoding rules to express instances of application-defined data types within the message
Defines an XML-based convention for representing the request to the remote service and the resulting response
The Web Services Description Language (WSDL) is a standardized XML format for describing network services. The description includes the name of the service, the location of the service, and ways to communicate with the service. WSDL service descriptions can be published on the Web. GlassFish Server provides a tool for generating the WSDL specification of a web service that uses remote procedure calls to communicate with clients.