Using Adapter Activators

When creating a new POA, the application developer may declare specific policy choices for the new POA and provide a different adapter activator and servant manager (these are callback objects used by the POA to activate POAs on demand and activate servants). Creating new POAs also allows the application developer to partition the name space of objects, as Object Ids are interpreted relative to a POA. Finally, by creating new POAs, the developer can independently control request processing for multiple sets of objects.

An adapter activator is optional. You would use an adapter activator if POAs need to be created during request processing. If all needed POAs are created when the application is initialized, an adapter activator is not required.

An adapter activator supplies a POA with the ability to create child POAs on demand, as a side-effect of receiving a request that names the child POA (or one of its children), or when the find_POA method is called with an activate parameter value of TRUE. The ORB will invoke an operation on an adapter activator when a request is received for a child POA that does not currently exist. The adapter activator can then create the required POA on demand.

A request must be capable of conveying the Object Id of the target object as well as the identification of the POA that created the target object reference. When a client issues a request, the ORB first locates an appropriate server (perhaps starting one if needed) and then it locates the appropriate POA within that server.

If the POA does not exist in the server process, the application has the opportunity to re-create the required POA by using an adapter activator. An adapter activator is a user-implemented object that can be associated with a POA. It is invoked by the ORB when a request is received for a nonexistent child POA. The adapter activator has the opportunity to create the required POA. If it does not, the client receives the ADAPTER_NONEXISTENT exception.

Once the ORB has located the appropriate POA, it delivers the request to that POA. The further processing of that request depends both upon the policies associated with that POA as well as the object's current state of activation.

An Example Using Adapter Activators

The following example code shows an application that uses Adapter Activators to enable the POA to be created during request processing. This application builds on the "Hello World" example. The following files are included in this example:

For instructions on running this example, see Running the Example Adapter Activator Application.

The code for the example client initializes the ORB, resolves HelloServant, and invokes the sayHello() method.

The code for the server does the following:


This Interface Definition Language (IDL) file is used in all of the "Hello World" example variations on this site. This IDL file describes a CORBA object whose sayHello() operation returns a string.

The servant is the implementation of the Hello IDL interface; each Hello instance is implemented by a HelloServant instance. The servant is a subclass of HelloPOA, which is generated by the idlj compiler from the example IDL. The servant contains one method for each IDL operation, in this example, the sayHello() method. Servant methods are just like ordinary Java methods; the extra code to deal with the ORB, with marshaling arguments and results, and so on, is provided by the skeleton.


The make program generates a sequence of commands for execution by the Unix shell.


The bat utility generates a sequence of commands for execution by the Microsoft Windows command shell.

Running the Example Adapter Activator Application

To run this example,

You will see output generated to the terminal window similar to that below when you run the Makefile:

Shut down ORBD when you have completed this example.

Further Information

For more information on Adapter Activators, please refer to section 11.3.3 of the CORBA 2.3.1 Specification or the AdapterActivatorOperations API documentation.

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