100

Processing Layer Design

E

The issues and considerations for designing an application's processing or 

business logic layer, such as whether to perform this logic in the Web or EJB 

tier, are the same whether or not you use a Web service.

We do not address these business logic design issues here, since much of this

discussion has already been covered in the book 

Designing Enterprise Applica 

tions with the J2EE

TM

 Platform, Second Edition

, and you can refer to that book for

general guidelines and recommendations. You should also refer to the BluePrints

Web site at 

http://java.sun.com/blueprints

 for recommendations on designing

an application's business processing logic. 

In addition to these general guidelines, there are some specific issues to keep

in mind when designing the processing layer of a Web service.

Keep the processing layer independent of the interaction layer

. By keeping 

the layers independent and loosely coupled, the processing layer remains ge 

neric and can support different types of clients, such as Web service clients, 

classic Web clients, and so forth. To achieve loose coupling between the lay 

ers, consider using delegate classes that encapsulate the access to business 

components. 

Bind XML documents to Java objects in the interaction layer

. There are 

times when your Web service expects to receive from a client an XML docu 

ment containing a complete request, but the service's business logic has no 

need to operate on the document. On these occasions, it is recommended that 

the interaction layer bind the XML document contents to Java objects before 

passing the request to the processing layer. Since the processing logic does not 

have to perform the XML to Java conversion, a single processing layer can 

support XML documents that rely on different schemas. This also makes it 

easy to support multiple versions of an XML schema.

Keep in mind that your processing logic can operate on the contents of an

XML document received from a client. Refer to  Handling XML Documents in a

Web Service  on page 105, which highlights issues to consider when you pass

XML documents to your business processing logic.

Depending on your application scenario, your processing layer may be

required to work with other Web service peers to complete a client's request. If so,

your processing layer effectively becomes a client of another Web service. Refer

to Chapter 5 for guidelines on Web service clients. In other circumstances, your