Chapter 5 Client Design

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Note in Figure 5.6 that a client accesses a Web service via the client side rep 

resentation of the service endpoint interface, while the JAX RPC runtime handles

the work of communicating with the respective service. A developer programs

against an interface, which provides a flexible way to access a service in a porta 

ble fashion.

E

Consider using the dynamic proxy approach if portability is important to your 

application, since this approach uses the service's endpoint interface to com 

municate with a service at runtime. Dynamic proxy communication is the most 

portable mode across JAX RPC implementations. 

E

Because of how they access a service at runtime, dynamic proxies may have 

additional overhead when calls are made. 

5.3.1.3

Using DII Call Interface

A client application may also dynamically access a Web service by locating the

service at runtime from a registry. The client does not know about the service when

it is compiled; instead, the client discovers the service's name from a JAXR registry

at runtime. Along with the name, the client discovers the required parameters and

return values for making a call to the service. Using a dynamic invocation interface,

the client locates the service and calls it at runtime. 

Generally, using DII is more difficult for a developer. A developer must work

with a more complex interface than with stubs or dynamic proxies. Not only does

this interface require more work on the part of the developer, it is more prone to

class cast exceptions. In addition, the DII approach may have slower access. A

developer may choose to use the DII approach when a complete WSDL document

is not available or provided, particularly when the WSDL document does not

specify ports. The DII approach is more suitable when used within a framework,

since from within a framework, client applications can generically and dynami 

cally access services with no changes to core application code.

Figure 5.7 shows how a client uses the JAXR API to look up the endpoint

WSDL for a service in a registry. The client uses the information from the registry

to construct a j

avax.xml.rpc.Call

, which it uses to access the Web service.