Chapter 3 Service Endpoint Design

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Discussions of Web service design issues in this chapter include references to

these examples and scenarios. However, the discussions use only appropriate

characteristics of these scenarios as they pertain to a particular design issue, and

they are not meant to represent a complete design of a scenario.

3.2

Flow of a Web Service Call

In a Web service scenario, a client makes a request to a particular Web service, such

as asking for the weather at a certain location, and the service, after processing the

request, sends a response to the client to fulfill the request. When both the client and

the Web service are implemented in a Java environment, the client makes the call to

the service by invoking a Java method, along with setting up and passing the

required parameters, and receives as the response the result of the method

invocation. 

To help you understand the context within which you design Web services,

let's first take a high level view at what happens beneath the hood in a typical

Web services implementation in a Java environment. Figure 3.1 shows how a Java

client communicates with a Java Web service on the J2EE 1.4 platform. 

Note:

 Figure 3.1 changes when a non Java client interacts with a Java Web

service. In such a case, the right side of the figure, which reflects the actions of the

Web service, stays the same as depicted here, but the left side of the figure would

reflect the actions of the client platform. When a Java client invokes a Web service

that is on a non Java platform, the right side of the figure changes to reflect the

Web service platform and the left side, which reflects the actions of the client,

remains as shown in the figure. 

Once the client knows how to access the service, the client makes a request to

the service by invoking a Java method, which is passed with its parameters to the

client side JAX RPC runtime. With the method call, the client is actually invoking

an operation on the service. These operations represent the different services of

interest to clients. The JAX RPC runtime maps the Java types to standard XML

types and forms a SOAP message that encapsulates the method call and parame 

ters. The runtime then passes the SOAP message through the SOAP handlers, if

there are any, and then to the server side service port. 

The client's request reaches the service through a port, since a port provides

access over a specific protocol and data format at a network endpoint consisting of

a host name and port number.