68

Designing a Service's Interaction Layer

it obviates the need to place the endpoint in its own tier where the presence of the

endpoint is solely to act as a proxy directing requests to other tiers that contain the

service's business logic.

When you develop a new Web service that does 

not

 use existing business

logic, choosing the endpoint type to use for the Web service interface is straight 

forward. The endpoint type choice depends on the nature of your business logic 

whether the business logic of the service is completely contained within either the

Web tier or the EJB tier:

E

Use a JAX RPC service endpoint when the processing layer is within the Web 

tier.

E

Use an EJB service endpoint when the processing layer is only on the EJB tier.

When you add a Web service interface to an existing application or service,

you must consider whether the existing application or service preprocesses

requests before delegating them to the business logic. If so, then keep the follow 

ing guideline in mind:

E

When you add a Web service interface for an existing application, choose an 

endpoint type suited for the tier on which the preprocessing logic occurs in the 

existing application. Use a JAX RPC service endpoint when the preprocessing 

occurs on the Web tier of the existing application and an EJB service endpoint 

when preprocessing occurs on the EJB tier.

If the existing application or service does not require preprocessing of the

incoming request, choose the appropriate endpoint that is present in the same tier

as the existing business logic. Besides these major considerations for choosing an

endpoint type, there are other, more subtle differences between an EJB service

endpoint and a JAX RPC service endpoint. You may find it helpful to keep in

mind these additional points when choosing a Web service endpoint type:

Multi threaded access considerations

 An EJB service endpoint, because it 

is implemented as a stateless session bean, need not worry about multi 

threaded access since the EJB container is required to serialize requests to any 

particular instance of a stateless session bean. For a JAX RPC service