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Developing Client Applications to Use a Web Service

5.3.1 Communication Modes for Accessing a Service

To best determine the communication mode for your client application, you need to

know the answers to the following two questions. Is the Web service's full WSDL

document known? Is the endpoint address for the Web service known? 

As indicated, there are three principal modes for a client application's commu 

nication with a Web service: stub, dynamic proxy, and dynamic invocation interface

(DII). By a communication mode, we mean the APIs for programmatically access 

ing a service via the 

javax.xml.rpc.Service

 interface. Clients using either the

stubs or dynamic proxies to access a service require the prior definition of a

service endpoint interface. Note that when we refer to the service endpoint inter 

face, which is the interface between the stub and dynamic proxy clients and the

JAX RPC API and stub, we are referring to the interface that represents the cli 

ent's view of a Web service.

When using stubs, a JAX RPC runtime tool generates during development

static stub classes that enable the service and the client to communicate. The stub,

which sits between the client and the client representation of the service endpoint

interface, is responsible for converting a request from a client to a SOAP message

and sending it to the service. The stub also converts responses from the service

endpoint, which it receives as SOAP messages, to a format understandable by the

client. In a sense, a stub is a local object that acts as a proxy for the service end 

point. 

Dynamic proxies provides the same functionality as the stubs, but do so in a

more dynamic fashion. Stubs and dynamic proxies both provide the developer

access to the 

javax.xml.rpc.Stub

 interface, which represents a service endpoint.

With both models, it is easy for a developer to program against the service endpoint

interface, particularly because the JAX RPC runtime does much of the communica 

tion work behind the scenes. The dynamic proxy model differs from the stub model

principally because the dynamic proxy model does not require code generation

during development. 

DII is a call interface that supports a programmatic invocation of JAX RPC

requests. Using DII, a client can call a service or a remote procedure on a service

without knowing at compile time the exact service name or the procedure's signa 

ture. A DII client can discover this information at runtime and can dynamically

look up the service and its remote procedures.

When using DII, clients can dynamically access a service at runtime. The

stubs rely on a tool that uses the WSDL file to create the service endpoint inter 

face, plus generate stub and other necessary classes. These generated classes elim