Java Remote Method Invocation: 3 - RMI System Overview - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

Java Remote Method Invocation

3.1 Stubs and Skeletons

RMI uses a standard mechanism (employed in RPC systems) for communicating with remote objects: stubs and skeletons. A stub for a remote object acts as a client's local representative or proxy for the remote object. The caller invokes a method on the local stub which is reponsible for carrying out the method call on the remote object. In RMI, a stub for a remote object implements the same set of remote interfaces that a remote object implements.
When a stub's method is invoked, it does the following:

initiates a connection with the remote VM containing the remote object.

marshals (writes and transmits) the parameters to the remote VM

waits for the result of the method invocation

unmarshals (reads) the return value or exception returned

returns the value to the caller

The stub hides the serialization of parameters and the network-level communication in order to present a simple invocation mechanism to the caller.
In the remote VM, each remote object may have a corresponding skeleton (in JDK1.2-only environments, skeletons are not required). The skeleton is responsible for dispatching the call to the actual remote object implementation. When a skeleton receives an incoming method invocation it does the following:

unmarshals (reads) the parameters for the remote method

invokes the method on the actual remote object implementation

marshals (writes and transmits) the result (return value or exception) to the caller

In JDK1.2 and additional stub protocol was introduced that eliminates the need for skeletons in JDK1.2-only environments. Instead, generic code is used to carry out the duties performed by skeletons in JDK1.1. Stubs and skeletons are generated by the rmic compiler.

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