Chapter 3 Service Endpoint Design

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How do these two approaches compare? Starting with Java interfaces and

creating a WSDL document is probably the easier of the two approaches. With

this approach, you need not know any WSDL details because you use vendor 

provided tools to create the WSDL description. While these tools make it easy for

you to generate WSDL files from Java interfaces, you do lose some control over

the WSDL file creation. 

E

With the Java to WSDL approach, keep in mind that the exposed service in 

terface may be too unstable from a service evolution point of view. 

With the Java to WSDL approach, it may be hard to evolve the service inter 

face without forcing a change in the corresponding WSDL document, and chang 

ing the WSDL might require rewriting the service's clients. These changes, and

the accompanying instability, can affect the interoperability of the service itself.

Since achieving interoperability is a prime reason to use Web services, the insta 

bility of the Java to WSDL approach is a major drawback. Also, keep in mind that

different tools may use different interpretations for certain Java types (for exam 

ple, 

java.util.Date

 might be interpreted as 

java.util.Calendar

), resulting in

different representations in the WSDL file. While not common, these representa 

tion variations may result in some semantic surprises.

On the other hand, the WSDL to Java approach gives you a powerful way to

expose a stable service interface that you can evolve with relative ease. Not only

does it give you greater design flexibility, the WSDL to Java approach also pro 

vides an ideal way for you to finalize all service details from method call types

and fault types to the schemas representing exchanged business documents 

before you even start a service or client implementation. Although a good knowl 

edge of WSDL and the WS I Basic Profile is required to properly describe these

Web services details, using available tools helps address these issues.

After you decide on the approach to take, you must still resolve other interface

design details, which are described in the next sections.

3.4.1.1

Choice of the Interface Endpoint Type

In the J2EE platform, you have two choices for implementing the Web service inter 

face you can use a JAX RPC service endpoint (also referred to as a Web tier end 

point) or an EJB service endpoint (also referred to as an EJB tier endpoint). Using

one of these endpoint types makes it possible to embed the endpoint in the same tier

as the service implementation. This simplifies the service implementation, because