Java Cookbook

Chapter 22. Distributed Java: RMI

Introduction

A distributed system is a program or set of programs that runs using more than one computing resource. Distributed computing covers a wide spectrum, from intra-process distributed applications (which Java calls threaded applications, discussed in Chapter 24), through intra-system applications (such as a network client and server on the same machine), to applications where a client program and a server program run on machines far apart (such as a web application).

Distributed computing was around for a long time before Java. Some traditional distributed mechanisms include RPC (remote procedure call) and CORBA. Java adds RMI (Remote Method Invocation), its own CORBA support, and EJB (Enterprise JavaBeans) to the mix. This chapter covers only RMI in detail, but these other technologies are discussed briefly.

At its simplest level, remote procedure call is the ability to run code on another machine and have it behave as much as possible like a local method call. Most versions of Unix use remote procedure calls extensively: Sun’s NFS, YP/NIS, and NIS+ are all built on top of Sun’s RPC. Windows NT implements large parts of the Unix DCE Remote Procedure Call and can interoperate with it. Each of these defines its own slightly ad hoc method of specifying the interface to the remote call. Sun’s RPC uses a program called rpcgen, which reads a protocol specification and writes both the client and server network code. These are both Unix-specific; ...