This chapter includes the following sections:
A Web service is a self-contained application that can be described, published, and invoked over a network, such as a corporate intranet or the Internet. Because you access Web services using standard Web protocols such as Extensible Markup Language (XML) and HTTP, the diverse and heterogeneous applications on the Web (which typically already understand XML and HTTP) can access Web services and communicate with each other automatically.
Major benefits of Web services include:
Interoperability among distributed applications that span diverse hardware and software platforms
Easy, widespread access to applications through firewalls using Web protocols
A cross-platform, cross-language data model (XML) that facilitates developing heterogeneous distributed applications
Web services are characterized by three factors:
What they do (the business functionality they expose)
How they can be accessed (the set of published interfaces necessary to use the exposed functionality)
Where they are (the Web site which exposes that functionality)
What the Web service can do (that is, the functionality it implements) is described in a standard XML vocabulary called Web Services Description Language (WSDL). For example, a banking Web service may implement functions to check an account, print a statement, and deposit and withdraw funds. These functions are described in a WSDL file that any consumer can invoke to access the banking Web service. As a result, a consumer does not have to know anything more about a Web service than the WSDL file that describes what it can do.
A Web service client (or consumer)--such as, a desktop application or a Java Platform, Enterprise Edition portlet-- invokes a Web service by submitting a request in the form of an XML document to the Web service. The Web service processes the request and returns the result to the Web service client in an XML document.
The Web service client can send a request in the form of a Simple Object Access Protocol (SOAP) message. SOAP is an XML messaging framework designed to allow heterogeneous applications to exchange structured information in a distributed environment. In turn, the Web service processes the request and returns the response in a SOAP message.
You can also develop Representational State Transfer (REST) Web services, or "RESTful" Web services. REST describes any simple interface that transmits data over a standardized interface (such as HTTP) without an additional messaging layer, such as SOAP. REST provides a set of design rules for creating stateless services that are viewed as resources, or sources of specific information, and can be identified by their unique URIs. A client accesses the resource using the URI, a standardized fixed set of methods, and a representation of the resource is returned. The client is said to transfer state with each new resource representation.
To secure the message exchange, the Web service may require credentials to access the service, for example a username and a password, or encrypt the response.
Web services rely on a set of XML-based industry standards, including the following:
XML, a data format that allows uniform communication between Web services consumers and Web services providers
XML Schema, a framework that describes XML vocabularies used in business transactions
SOAP, a protocol for exchanging structured information in the implementation of Web services
WSDL, an XML-based language providing a model for describing Web services
WS-Policy, a framework that provides a flexible and extensible grammar for describing the capabilities, requirements, and general characteristics of Web services using policies
Table 11-1 Roadmap for Web Services
| Major Task | Subtasks and Additional Information |
|---|---|
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Learning more about WebLogic Web Services |
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Using the samples (for WebLogic Web service developers) |
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Developing Web services using JAX-WS |
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Developing RESTful Web services |
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Developing Web services using JAX-RPC |
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Deploying and administering WebLogic Web services |
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Securing WebLogic Web services |
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Interoperability with WebLogic Web services |