Java Examples in a Nutshell, 3rd Edition

Advanced RMI

There are several advanced features of RMI that are beyond the scope of this book but are important to know about. I’m only going to describe these features briefly here; you should consult Java Enterprise in a Nutshell for details.

Remote Class Loading

Ideally, a client of a remote object should need only direct access to the remote interface; it should not need to know anything about the implementation of that interface. In the examples we’ve seen in this chapter, however, the client requires access to the implementation stub class as well. (And in practice, you’ve probably run the client and the server on the same machine with the same class path, so they shared all classes.)

Having to distribute implementation stubs with RMI client programs can be a burden, especially when the server implementation changes. Fortunately, RMI provides a mechanism that allows a client to remotely load the stub classes it needs from a network server. Unfortunately, making this work takes a fair bit of effort. First, you must have a web server running and make the stub classes available for download from that server. Second, you must install a security manager in all your clients to protect against malicious code in the downloaded stub classes (and remember that an RMI server that uses other remote objects is itself an RMI client). Third, since you’ve installed a security manager, you must explicitly specify a security policy that allows your RMI clients to make the network connections ...