You need to create a distributed object(via CORBA) in the C++ application that exposes the data that you're interested in. On the Java side, you need to connect to this distributed object using a client stub.
You write one idl that defines the interface for accessing the C++ application. You use a idl-to-java compiler to generate the client stubs for Java and a idl-to-C++ compiler to generate the server skeletons for C++. I've used the idl-to-java compiler, but I've never used to idl-to-C++ compiler.
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