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2.2.1 Application Objects

 

An application object encapsulates all application-specific logic for initialization and for handling incoming requests. Since application objects are stateless, the number of available application objects for processing client requests can be restricted to a predefined maximum number.

 
Figure 2

Figure 2: Initialization process of application objects  
 

An application object can be configured by attribute values which can be defined in a special property file called ApplicationObjects.properties. In the upper part of Figure 2, an extract of the file with two application objects is depicted. In the lower part of Figure 2, the hierarchical structure of the property file is illustrated. Basically there are attribute values related to RESPONDEO and to application objects in general. The second parameter (class name) is the class name of an application object which is loaded dynamically into RESPONDEO during the process of initialization. The rest of the parameters are application-specific name-value pairs which are passed through to the specified application object as a black-box. This strategy can be applied iteratively as shown for the application object Pool. A pool is a special application object managing a set of application objects of the same type. It has to have two parameters called member and poolsize, which respectively specify the type of the application object and the number of application objects in the pool.

Each parameter is accessed by a general function which provides a stable and unique interface to all application objects. The actual management of application-specific parameters is left up to the application object's implementation. In addition, the ability to obtain parameter information via a general function enables the development of flexible collections of application objects that can be changed and adapted even at run-time by applying the initialization mechanism as described above.

RESPONDEO provides a naming service that maps a symbolic name to a set of application objects. The symbolic name, shown in Figure 2 as the first property value (DebisCerberus1, RandomProgressAlgorithms) of each application object, provides independent ways to bind to an application object, i.e. for availability, improved performance and for reusing existing application objects in various application contexts. The symbolic name can change over time and is accessed via the general function mentioned above. In Section 4 examples of application objects are illustrated.


next up previous
Next: 2.2.2 Application Management Functionalities Up: RESPONDEO - A Lightweight Previous: RESPONDEO - A Lightweight

Ralf-Dieter Schimkat
Thu Dec 9 14:08:00 GMT+1 1999