214

Developing Client Applications to Use a Web Service

The J2ME environment differs somewhat. Applications in J2ME environ 

ments can use only stubs to access Web services, and stubs are portable for J2ME

devices. The JAX RPC profile for J2ME environments does not support dynamic

proxies and DII. 

Although at this time stubs are not portable across J2EE implementations, the

next version of JAX RPC is expected to address this portability issue.

E

Using stubs, especially in a Java environment, is often the easiest because the 

developer can work with generated class files representing the service method 

call parameters and return values. However, the greater dependencies between 

the client and the Web service may lead to problems if the service interface 

changes frequently. This mode also requires that stub classes be generated be 

fore compiling the application.

5.3.1.2

Using Dynamic Proxy Communication

The dynamic proxies are similar in many ways to the stubs previously described.

However, unlike stubs, the client developer needs only the client side interface that

matches the service endpoint interface. That is, clients using dynamic proxies

program to an interface that ensures the client application is portable across other

JAX RPC runtime implementations. Developers using dynamic proxies must

create Java classes to serve as JAX RPC value types these classes have an

empty constructor and set methods for each field, similar to JavaBeans classes.

The dynamic proxy is based on the service endpoint interface, its WSDL doc 

ument, and a JAX RPC mapping file (similar to the stubs model). (See Figure

5.6.) Client applications can access the Web service ports using the

javax.xml.rpc.Service

 method 

getPort

.

Client

Service Endpoint Interface

WSDL

JAX RPC

(client side representation)

Mappings

JAX RPC Runtime

Web Service

Figure 5.6

Accessing a Service Using a Dynamic Proxy