• Web Service - SOAP
  • What is Web Service
  • Web Services Example
  • What is SOAP
    • SOAP Structure
    • SOAP Message
    • WSDL
    • UDDI
  • Code Example
  • Links

Web Service - SOAP

What is Web Service

“A Web service is a method of communication between two electronic devices over a network.”

Common Type: SOAP web service, RESTful web service

Web Service is used primarily as a means for businesses to communicate with each other and with clients, Web services allow organizations to communicate data without intimate knowledge of each other’s IT systems behind the firewall.

总结来说，就是公司内的部门A和部门B，或者公司X和公司Y，为了某一些数据互通，开发的一个数据通信模块。

Web Services Example

Register/Ordering

Consider a simple account-management and order processing system. The accounting personnel use a client application built with Visual Basic or JSP to create new accounts and enter new customer orders.

The processing logic for this system is written in Java and resides on a Solaris machine, which also interacts with a database to store information.

Client(VB) -> account registration
	-> SOAP ->
DB Command -> Server & DB(Java)

The steps to perform this operation are as follows:

• The client program bundles the account registration information into a SOAP message.
• This SOAP message is sent to the web service as the body of an HTTP POST request.
• The web service unpacks the SOAP request and converts it into a command that the application can understand.
• The application processes the information as required and responds with a new unique account number for that customer.
• Next, the web service packages the response into another SOAP message, which it sends back to the client program in response to its HTTP request.
• The client program unpacks the SOAP message to obtain the results of the account registration process.

http://www.tutorialspoint.com/webservices/what_are_web_services.htm

What is SOAP

Simple Object Access Protocol

• based on XML
• a communication protocol between applications
• a format for sending messages
• platform independent, language independent

SOAP Structure

In the example of SOAP web service

• Data type: SOAP in XML
• Transmit protocol: HTTP
• Interface packages: WSDL
• Lookup Directory: UDDI

SOAP是比较早期的Web Service解决方案，后来慢慢就淘汰了，主要原因是“重”，开发起来复杂，学习成本高。

这个“重”主要体现在几个方面：

• SOAP有自己的一套XML格式的SOAP message，需要额外parse；而RESTful就是直接JSON/XML/CSV，使用起来方便很多。
• SOAP需要定义一套接口WSDL暴露给外部；而RESTful直接使用HTTP verbs(GET, PUT, POST, DELETE)，进而提出 Resource-based 这个概念，更容易开发。
• SOAP需要定义一套资源中心UDDI暴露给外部，用来查询WSDL；而RESTful没有这些，它的请求可以通过文档直接暴露给外部。

总结来看，SOAP参考了很多Java API的编程思想，比如RMI/RPC，以及JNDI等等。它想成为一个非常规范的web service框架，但是有点over design了，开发起来比较麻烦，是一个技术发展的中间产物。现在，RESTful基本已经替代它了。

个人认为，REST能战胜SOAP的很大一个原因是，它没有重复造轮子，而是使用了现有的轮子，以一种新的方式组合起来，且足够简洁，直接描述出了web service的本质。

SOAP Message

A SOAP message is an ordinary XML document containing the following elements:

• An Envelope element that identifies the XML document as a SOAP message
• A Header element that contains header information
• A Body element that contains call and response information
• A Fault element containing errors and status information

<?xml version="1.0"?>
<soap:Envelope
xmlns:soap="http://www.w3.org/2001/12/soap-envelope"
soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">

<soap:Header>
  ...
</soap:Header>

<soap:Body>
  ...
  <soap:Fault>
  ...
  </soap:Fault>
</soap:Body>

</soap:Envelope>

WSDL

Web Services Description Language It is just a simple XML document. The description includes the name of the service, the location of the service, and ways to communicate with the service.

Document Structure

<definitions>

<types>
  data type definitions........
</types>

<message>
  definition of the data being communicated....
</message>

<portType>
  set of operations......
</portType>

<binding>
  protocol and data format specification....
</binding>

</definitions>

UDDI

Universal Description, Discovery and Integration

a directory service where businesses can register and search for Web services

Code Example

Create a Web Service with Server & Client

JAX-WS

• JAX-WS Five Minute Tutorial
• Create JAXWS Web Services - see src

Steps:

• Server Side:
  • Create Endpoint Interface using @WebService and @WebMethod ->
  • Create Endpoint Implementation class ->
  • Create Endpoint Publisher using Endpoint.publish("url",new impl());
• Client Side:
  • Generate the client stubs using wsimport -s . url
  • Call the web service -> new Impl() -> getImplPort()

Eclipse

• Create SOAP Web Services using eclipse
• How to Create Sample WSDL in Eclipse and Generate Client

Spring

• Consume Spring SOAP W.S - Local: WSWeatherDemo
• Build Spring SOAP W.S

Links

• Web Service Tutorial
• Where to use Web Services