The RMI protocol

The RMI protocol uses a combination of two other protocols to turn simple method invocations into remote method invocations:

Object Serialization
HTTP

The object serialization protocol is used to marshal data and the HTTP protocol is used to post a remote method invocation.

Overview of RMI Interfaces and Classes

The Remote Interface

The interface java.rmi.Remote is a marker interface that contains no methods:

public interface Remote {}

This interface is used to identify objects that can be referenced remotely. All remote objects must directly or indirectly implement this interface. A single class can implement more than one remote interface. The following is an example that declares one method that can be invoked remotely.

public interface RemoteInterface extends Remote{

public String remoteMethod1()throws RemoteException;

}

The RemoteException Class

The class RemoteException is the superclass for a number of communication-related exceptions that may occur during the execution of a remote method call. Each method of a remote interface must list RemoteException in its throws clause. RemoteException is a checked exception.

The RemoteObject Class

RMI server functions are provided by the java.rmi.server.RemoteObject and its subclasses, java.rmi.server.RemoteServer, java.rmi.server.UnicastRemoteObject. The RemoteObject class implements the java.lang.Object behavior for remote objects. RemoteObject class provides the remote semantics of Object by implementing methods for hashCode(), equals(), and toString(). RemoteObject class is abstract, so it cannot be instantiated.

Methods

• public RemoteRef getRef() - Returns the remote reference for the remote object.

• public static Remote toStub(Remote obj) - Returns the stub for the remote object "obj" passed as a parameter. This operation is only valid after the object has been exported.

The RemoteServer Class

The java.rmi.server.RemoteServer class is the super class of the server implementation classes java.rmi.server.UnicastRemoteObject and java.rmi.activation.Activatable. Subclasses of RemoteServer handle the tasks of exporting the remote object. RemoteServer class is abstract, so it cannot be instantiated.

Methods

• public static String getClientHost() - Returns the hostname of the client calling the method.

• public static void setLog(OutputStream out) - This method enables to set the log output stream. If out is null, call logging is turned off.

• public static PrintStream getLog() - Returns stream for the RMI call log, so that application-specific information can be written to the call log in a synchronized manner.