This document was not updated for this
J2SETM release.
When updated, topics in this section will include:
For a client to invoke a CORBA object operation, both the client and the server (the object implementation) must use a CORBA software component called an ORB (object request broker). ORBs are the common denominators that bridge the differences in location, platform, and programming language that can separate a client and a server. ORBs can contact each other across the network, can create and interpret object references (CORBA object handles), and can marshal parameters into and out of the format used by IIOP. In addition to enabling client/server communication, ORBs provide other services, but they are not described here.
The two ways to invoke an operation on a CORBA object are:
To make a static invocation on a CORBA object, a Java client needs an object reference to the servant that performs the operation. The object reference has two important functions:
OMG IDL is the language in which CORBA object interfaces are
defined. For each OMG IDL module, the idlj compiler
generates a Java package. For each interface Foo defined
in an OMG IDL module, the generated package contains the following
items of interest to the client programmer:
Foo, which extends
org.omg.portable.IDLEntity, org.omg.CORBA.Object, and the
operations interface. The signature interface is used as the signature type in
method declarations when interfaces of the specified type are used in other
interfaces. From the client's point
of view, an object reference for a CORBA Foo object
implements this interface.
Note: The Stub implements the Foo interface, where it
generates code for each method to marshall the arguments,
invoke the method, and then unmarshall the arguments.
FooOperations, which is used
in the server-side mapping and as a mechanism for providing optimized calls for
co-located clients and server. The server developer provides implementation for the
methods indicated by the operations interface.
Note: The server writer usually extends FooPOA and provides
implementation for the methods provided by the operations interface.
FooHelper, that defines auxiliary
methods, notably narrow(), which is the CORBA
counterpart of Java casting.
CORBA dynamic invocation uses an object called a request to
hold everything pertinent to an invocation: the object reference, the
name of the operation, its parameters, and space for the result. The
client builds a request object describing an operation, then calls
the request's invoke method, which dispatches the
request just as a stub would. When the invoke method returns, the
result is available in the request object.
The key to dynamic invocation is the ability of requests to hold
self-describing data. This facility enables a request object to
represent any invocation of any operation, regardless of its
parameters. Each self-describing data element has a special type
known in OMG IDL as Any. An Any consists of
a typecode (whose values are defined by OMG IDL) and a value; the
typecode specifies the type of the value.
Clients | Servers | Exceptions | Initialization | Naming
Home |
Fundamentals |
Programming |
References |
Tutorial |