Rmi

Remote Method Invocation (RMI) is a Java API that enables an object in one Java Virtual Machine (JVM) to invoke methods on an object located in another JVM as if the remote object were local. Remote methods must be declared in interfaces that extend java.rmi.Remote, and their declared remote methods throw java.rmi.RemoteException or its subclasses. The RMI framework handles remote communication, parameter marshaling, and result unmarshalling.

Core components include remote interfaces, remote objects, the RMI registry, and client stubs. A server exports a remote object, for example by extending UnicastRemoteObject or by calling exportObject. Clients obtain a remote reference by looking up the object’s name in the RMI registry, which acts as a simple naming service. Historically, skeleton classes accompanied stubs to dispatch calls, but modern RMI uses dynamic proxies and generates skeletons as needed.

Communication uses the Java Remote Method Protocol (JRMP) by default, over TCP. When a client invokes a method on the remote stub, the call is serialized, transmitted to the server, executed on the remote object, and the result or exception is returned to the client. The process is synchronous and designed to be transparent to the programmer, aside from handling RemoteException and potential network errors.

Security and portability considerations include the reliability of Java serialization and the need for appropriate security manager configuration to restrict access. RMI provides Java-to-Java interoperability, but cross-language compatibility is limited unless using variants such as RMI-IIOP (RMI over IIOP) to interface with CORBA.

RMI has been a staple of Java distributed applications since the early platform. While newer frameworks have emerged, RMI remains in use for legacy systems and Java-only distributed object communication.