http://patriot.net/~tvalesky/easyrmi.html

a review by Lan Chen

This article gives a very simple and good example of how to make a RMI program in JAVA. It provide the basic structure of a RMI program for beginners , so they can imitate the structure and get started. However, since RMI is one of the complex system i n java. It required a good understanding of RPC in order to understand RMI.

How java’s RMI related to Distributed System
Distributed system required tasks running in different address space and virtual machines. In java, there are two method to do this. First is socket. But sockets require client and server to work at application level protocols and message exchanging, w hich requires much detail work. The other is RMI. RMI is based on RPC. RPC abstracts the details to the level of a procedure call. The difference between two is RMI is for object system.

How RMI works
As introduced in the article, there is an simple client-server example

Client side: Client has at least two class. One is the client’s interface for accessing the server’s method. There is no implementation in the interface, just give out the signature.

The other is client program. It uses “lookup” to find the remote object by name in the server’s registry. Then it can access server object through the interface.

Server side: Server should first have a class to implement the interface. Then server also need a program to create an instance of the implementation.

More comparison for RPC and RMI
The basic structure of RPC is as follows:

In java’s RMI, the client access the interface. The rmic complier will automatic generate the client stub and server skeleton. And programmer does not need to consider the communication details. The main structure is nearly same as the above figure, ex cept for its OOP feature.

To conclude, the article is merely a simple introduction for RMI programming. Because of the close relationship between RPC and RMI, to learn RMI would also give a more down-to-ground understanding on how the RPC can be implemented. So I think it is r eally worth to know a little bit of RMI as a supplement of this course.