Develop CORBA programs using J2SE1.4
The J2SE1.4 version of Java2 introduces many new features and improvements for General Object Request Agent Structure (CORBA). New features and improvements are not only reflected in the modification of the standard CORBA specification, but also in an increase in the performance of existing characteristics. A newly added important feature is a lightweight object adapter (POA).
Corba new features
As early as 1990, CORBA has become the foundation of distributed applications. In the development of more than a decade, many important new features have been gradually added to the Corba 2.2 and updated versions. One of the new supplementary features is a lightweight object adapter (POA), which is defined in the CORBA 2.2 specification.
Lightweight object adapter
Until the CORBA version 2.1, the Same Management Organization (OMG) defined in CORBA has only the base object adapter (BOA), which provides a basic method for creating different types of CORBA objects. But all ORB providers and developers have found that BOA has some blurred in some respects and does not implement some of their desired features. This has developed its own expansion program, so the transplantation between different ORB implementations is difficult. The new standard object adapter is a lightweight object adapter (POA) that enables developers to create objects, and can be easily accepted between different ORB products provided by different developers. Poa is an intermediary program between ORB and server programs, as shown in Figure 1.
Figure 1 Disquest based on PoA
The client calls the target object reference, and then sends a request. After the ORB obtains this request, assign the request to the POA, determine the target object by POA. POA assists the request to the server, the server executes the request and returns the result to the POA, and the POA is sent to the ORB, and finally transmit it to the client. Since a program may have a lot of POA, in order to send the ORB to the correct POA, it needs to use the object keyword, an identifier, and the object keyword is saved in an object reference as part of the request content. Object Keywords contain an important content ie object ID, POA uses it to specify associations between target objects and servers (this association may be saved in the mapping).
