RMI and CORBA

 Java RMI is a mechanism that allows one to invoke a method on an object that exists in another address space. The other address space could be on the same machine or a different one. The RMI mechanism is basically an object-oriented RPC mechanism. CORBA is another object-oriented RPC mechanism. CORBA differs from Java RMI in a number of ways:

1. CORBA is a language-independent standard.
2. CORBA includes many other mechanisms in its standard (such as a standard for TP monitors) none of which are part of Java RMI.
3. There is also no notion of an "object request broker" in Java RMI.

Java RMI has recently been evolving toward becoming more compatible with CORBA. In particular, there is now a form of RMI called RMI/IIOP ("RMI over IIOP") that uses the Internet Inter-ORB Protocol (IIOP) of CORBA as the underlying protocol for RMI communication.
This tutorial attempts to show the essence of RMI, without discussing any extraneous features. Sun has provided a Guide to RMI, but it includes a lot of material that is not relevant to RMI itself. For example, it discusses how to incorporate RMI into an Applet, how to use packages and how to place compiled classes in a different directory than the source code. All of these are interesting in themselves, but they have nothing at all to do with RMI. As a result, Sun's guide is unnecessarily confusing. Moreover, Sun's guide and examples omit a number of details that are important for RMI.
There are three processes that participate in supporting remote method invocation.

1. The Client is the process that is invoking a method on a remote object.
2. The Server is the process that owns the remote object. The remote object is an ordinary object in the address space of the server process.
3. The Object Registry is a name server that relates objects with names. Objects are registered with the Object Registry. Once an object has been registered, one can use the Object Registry to obtain access to a remote object using the name of the object.