[Web Service]-淺談Web Service

Introduction to Web Services
                                                                      from NetBeans Web Service tutorials
Web services are distributed application components that are externally available. You can use them to integrate computer applications that are written in different languages and run on different platforms. Web services are language and platform independent because vendors have agreed on common web service standards.
Several programing models are available to web service developers. These models fall into two categories, both supported by the IDE:

• REST-based. REpresentational State Transfer is a new way to create and communicate with web services. In REST, resources have URIs and are manipulated through HTTP header operations.
• SOAP/WSDL-based. In traditional web service models, web service interfaces are exposed through WSDL documents (a type of XML), which have URLs. Subsequent message exchange is in SOAP, another type of XML document.

RESTful Web Services
REST-based ("RESTful") web services are collections of web resources identified by URIs. Every document and every process is modeled as a web resource with a unique URI. These web resources are manipulated by the actions that can be specified in an HTTP header. Neither SOAP, nor WSDL, nor WS-* standards are used. Instead, message exchange can be conducted in any format—XML, JSON, HTML, etc. In many cases a web browser can serve as the client.

HTTP is the protocol in REST. Only four methods are available: GET, PUT, POST, and DELETE. Requests can be bookmarked and responses can be cached. A network administrator can easily follow what is going on with a RESTful service just by looking at the HTTP headers.

REST is a suitable technology for applications that do not require security beyond what is available in the HTTP infrastructure and where HTTP is the appropriate protocol. REST services can still deliver sophisticated functionality. Flickr, Google Maps and Amazon all provide RESTful web services. NetBeans IDE Software as a Service (SaaS) functionality lets you use Facebook, Zillow, and other third-party-provided services in your own applications.

SOAP-based Web Services
In SOAP-based web services, Java utilites create a WSDL file based on the Java code in the web service. The WSDL is exposed on the net. Parties interested in using the web service create a Java client based on the WSDL. Messages are exchanged in SOAP format. The range of operations that can be passed in SOAP is much broader than what is available in REST, especially in security.

SOAP-based web services are suitable for heavyweight applications using complicated operations and for applications requiring sophisticated security, reliability or other WS-* standards-supported features. They are also suitable when a transport protocol other than HTTP has to be used. Many of Amazon's web services, particularly those involving commercial transactions, and the web services used by banks and government agencies are SOAP-based.

The Java API for XML Web Services (JAX-WS) is the current model for SOAP-based web services in Metro. JAX-WS is built on the earlier JAX-RPC model but uses specific Java EE 5 features, such as annotations, to simplify the task of developing web services. Because it uses SOAP for messaging, JAX-WS is transport neutral. It also supports a wide range of modular WS-* specifications, such as WS-Security and WS-ReliableMessaging.