3.1 Overview

The RMI system consists of three layers: the stub/skeleton layer, the remote reference layer, and the transport layer. The boundary at each layer is defined by a specific interface and protocol; each layer, therefore, is independent of the next and can be replaced by an alternate implementation without affecting the other layers in the system. For example, the current transport implementation is TCP-based (using Java sockets), but a transport based on UDP could be substituted.

To accomplish transparent transmission of objects from one address space to another, the technique of object serialization (designed specifically for the Java language) is used. Object serialization is described in this chapter only with regard to its use for marshaling primitives and objects. For complete details, see the Object Serialization Specification.

Another technique, called dynamic stub loading, is used to support client-side stubs which implement the same set of remote interfaces as a remote object itself. This technique, used when a stub of the exact type is not already available to the client, allows a client to use the Java language's built-in operators for casting and type-checking.