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inhibit server shutdown and impact performance. To alleviate this problem, the 

work management contract enables the application server to pool and reuse 

threads, similar to pooling and reusing connections. 

In addition, the work management contract gives resource adapters more flex 

ibility for using threads. The resource adapter can specify the execution con 

text for a thread. The contract allows a requesting thread to block stop its own 

execution until a work thread completes. Or, a requesting thread can block 

while it waits to get a work thread; when the application server provides a work 

thread, both the requesting and work threads execute in parallel. Yet another 

option, a resource adapter can submit the work for the thread to a queue and 

have it execute at some later point; the adapter continues its own execution 

without waiting further. Thus, a resource adapter and a thread may execute in 

conjunction with each other or independently, using a listener mechanism, if 

need be, to notify the resource adapter that the work thread has completed. 

  Lifecycle management contract Enables an application server to manage the 

lifecycle of a resource adapter. With this contract, the application server has a 

mechanism to bootstrap a resource adapter instance at deployment or at server 

startup, and to notify the adapter instance when it is undeployed or when the 

server is shutting down.

6.2.4 Web Service and XML Technologies

Although messaging systems provide many of the same EAI advantages as Web ser 

vices, Web services go a step further. Principally, Web services support multiple

vendors and the ability to go through firewalls using Internet standards. Web ser 

vices also support a flexible XML format. 

The J2EE 1.4 platform provides a rich set of Web service APIs and XML doc 

ument manipulating technologies. The Web service APIs JAX RPC, JAXR,

SAAJ, JAXB, and JAXP provide standard Java APIs for integrating applica 

tions and other systems. A Java application can use these APIs to obtain and use a

Web service. These APIs are particularly useful when an application or system

exposes a Web service layer explicitly for integration purposes.

There are also a number of XML related APIs and facilities in the Java lan 

guage (and the J2EE 1.4 platform) that can be applied to integration problems.

They permit you to define an interface data model, manipulate disparate docu 

ments, and perform transformations between data types. These XML APIs give

you the ability to structure a data model for passing data among different systems.

Chapter 2 discusses these technologies in greater depth.