Chapter 3 Service Endpoint Design

107

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It is important to consider the processing time for a request and whether the cli 

ent waits for the response. When a service expects an XML document as input 

and starts a lengthy business process based on the document contents, then cli 

ents typically do not want to wait for the response. Good design when process 

ing time may be extensive is to delegate a request to a JMS queue or topic and 

return a correlation identifier for the client's future reference. (Recall Figure 

3.7 on page 96 and its discussion.) 

The following sections discuss other considerations.

3.7.1 Exchanging XML Documents

As noted earlier, there are times when you may have to exchange XML documents

as part of your Web service and such documents are received as parameters of a

method call. The J2EE platform provides three ways to exchange XML documents. 

The first option is to use the Java MIME mappings provided by the J2EE plat 

form. See Table 3.1 on page 75. With this option, the Web service endpoint

receives documents as 

javax.xml.transform.Source

 objects. (See Code Example

3.3 on page 75.) Along with the document, the service endpoint can also expect to

receive other JAX RPC arguments containing metadata, processing requirements,

security information, and so forth. When an XML document is passed as a 

Source

object, the container automatically handles the document as an attachment 

effectively, the container implementation handles the document passing details

for you. This frees you from the intricacies of sending and retrieving documents

as part of the endpoint's request/response handling.

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Passing XML documents as 

Source

 objects is the most effective option in a 

completely Java based environment (one in which all Web service clients are 

based on Java). However, sending documents as 

Source

 objects may not be in 

teroperable with non Java clients. (As already noted in the section  Interoper 

ability  on page 86, standard ways to exchange attachments are currently being 

formulated. Future versions of the J2EE platform will incorporate these stan 

dards once they are final.)

The second option is to design your service endpoint such that it receives doc 

uments as 

String

 types. Code Example 3.17 shows the WSDL description for a

service that receives documents as String types, illustrating how the WSDL maps

the XML document.