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Designing a Service's Interaction Layer

sion bean. A JAX RPC service endpoint, on the other hand, does not have a 

facility for declaring method level access constraints, requiring you to do this 

programmatically. See Chapter 7 for more information.

HTTP session access considerations

 A JAX RPC service endpoint, 

because it runs in the Web container, has complete access to an 

HttpSession

object. Access to an 

HttpSession

 object, which can be used to embed cookies 

and store client state, may help you build session aware clients. An EJB 

service endpoint, which runs in the EJB container, has no such access to Web 

container state. However, generally HTTP session support is appropriate for 

short duration conversational interactions, whereas Web services often 

represent business processes with longer durations and hence need additional 

mechanisms. See  Correlating Messages  on page 359 for one such strategy.

3.4.1.2

Granularity of Service

Much of the design of a Web service interface involves designing the service's oper 

ations, or its methods. You first determine the service's operations, then define the

method signature for each operation. That is, you define each operation's parame 

ters, its return values, and any errors or exceptions it may generate. 

E

It is important to consider the granularity of the service's operations when de 

signing your Web service interface.

For those Web services that implement a business process, the nature of the

business process itself often dictates the service's granularity. Business processes

that exchange documents, such as purchase orders and invoices, by their nature

result in a Web service interface that is coarse grained. With more interactive Web

services, you need to carefully choose the granularity of these operations.

You should keep the same considerations in mind when designing the

methods for a Web service as when designing the methods of a remote enterprise

bean. This is particularly true not only regarding the impact of remote access on

performance but also with Web services; it is important with Web services

because there is an underlying XML representation requiring parsing and taking

bandwidth. Thus, a good rule is to define the Web service's interface for optimal

granularity of its operations; that is, find the right balance between coarse grained

and fine grained granularity.