Class UnicastRemoteObject

public class UnicastRemoteObject
extends RemoteServer

Used for exporting a remote object with JRMP and obtaining a stub that communicates to the remote object. Stubs are either generated at runtime using dynamic proxy objects, or they are generated statically at build time, typically using the rmic tool.

Deprecated: Static Stubs. Support for statically generated stubs is deprecated. This includes the API in this class that requires the use of static stubs, as well as the runtime support for loading static stubs. Generating stubs dynamically is preferred, using one of the five non-deprecated ways of exporting objects as listed below. Do not run rmic to generate static stub classes. It is unnecessary, and it is also deprecated.

There are six ways to export remote objects:

1. Subclassing UnicastRemoteObject and calling the UnicastRemoteObject() constructor.
2. Subclassing UnicastRemoteObject and calling the UnicastRemoteObject(port) constructor.
3. Subclassing UnicastRemoteObject and calling the UnicastRemoteObject(port, csf, ssf) constructor.
4. Calling the exportObject(Remote) method. Deprecated.
5. Calling the exportObject(Remote, port) method.
6. Calling the exportObject(Remote, port, csf, ssf) method.

The fourth technique, exportObject(Remote), always uses statically generated stubs and is deprecated.

The other five techniques all use the following approach: if the java.rmi.server.ignoreStubClasses property is true (case insensitive) or if a static stub cannot be found, stubs are generated dynamically using Proxy objects. Otherwise, static stubs are used.

The default value of the java.rmi.server.ignoreStubClasses property is false.

Statically generated stubs are typically pregenerated from the remote object's class using the rmic tool. A static stub is loaded and an instance of that stub class is constructed as described below.

• A "root class" is determined as follows: if the remote object's class directly implements an interface that extends Remote, then the remote object's class is the root class; otherwise, the root class is the most derived superclass of the remote object's class that directly implements an interface that extends Remote.
• The name of the stub class to load is determined by concatenating the binary name of the root class with the suffix _Stub.
• The stub class is loaded by name using the class loader of the root class. The stub class must extend RemoteStub and must have a public constructor that has one parameter of type RemoteRef.
• Finally, an instance of the stub class is constructed with a RemoteRef.
• If the appropriate stub class could not be found, or if the stub class could not be loaded, or if a problem occurs creating the stub instance, a StubNotFoundException is thrown.

Stubs are dynamically generated by constructing an instance of a Proxy with the following characteristics:

• The proxy's class is defined by the class loader of the remote object's class.
• The proxy implements all the remote interfaces implemented by the remote object's class.
• The proxy's invocation handler is a RemoteObjectInvocationHandler instance constructed with a RemoteRef.
• If the proxy could not be created, a StubNotFoundException will be thrown.

Constructors

UnicastRemoteObject

protected UnicastRemoteObject()
                       throws RemoteException

Throws:

RemoteException - if failed to export object

Since:

JDK1.1

UnicastRemoteObject

protected UnicastRemoteObject(int port)
                       throws RemoteException

Parameters:

port - the port number on which the remote object receives calls (if port is zero, an anonymous port is chosen)

Throws:

RemoteException - if failed to export object

Since:

1.2

UnicastRemoteObject

protected UnicastRemoteObject(int port,
                              RMIClientSocketFactory csf,
                              RMIServerSocketFactory ssf)
                       throws RemoteException

Parameters:

port - the port number on which the remote object receives calls (if port is zero, an anonymous port is chosen)

csf - the client-side socket factory for making calls to the remote object

ssf - the server-side socket factory for receiving remote calls

Throws:

RemoteException - if failed to export object

Since:

1.2

Methods

clone

public Object clone()
             throws CloneNotSupportedException

Returns a clone of the remote object that is distinct from the original.

Overrides:

clone in class Object

Returns:

the new remote object

Throws:

CloneNotSupportedException - if clone failed due to a RemoteException.

Since:

JDK1.1

See Also:

Cloneable

exportObject

@Deprecated
public static RemoteStub exportObject(Remote obj)
                                           throws RemoteException

Deprecated. This method is deprecated because it supports only static stubs. Use exportObject(Remote, port) or exportObject(Remote, port, csf, ssf) instead.

Parameters:

obj - the remote object to be exported

Returns:

remote object stub

Throws:

RemoteException - if export fails

Since:

JDK1.1

exportObject

public static Remote exportObject(Remote obj,
                                  int port)
                           throws RemoteException

Parameters:

obj - the remote object to be exported

port - the port to export the object on

Returns:

remote object stub

Throws:

RemoteException - if export fails

Since:

1.2

exportObject

public static Remote exportObject(Remote obj,
                                  int port,
                                  RMIClientSocketFactory csf,
                                  RMIServerSocketFactory ssf)
                           throws RemoteException

Parameters:

obj - the remote object to be exported

port - the port to export the object on

csf - the client-side socket factory for making calls to the remote object

ssf - the server-side socket factory for receiving remote calls

Returns:

remote object stub

Throws:

RemoteException - if export fails

Since:

1.2

unexportObject

public static boolean unexportObject(Remote obj,
                                     boolean force)
                              throws NoSuchObjectException

Removes the remote object, obj, from the RMI runtime. If successful, the object can no longer accept incoming RMI calls. If the force parameter is true, the object is forcibly unexported even if there are pending calls to the remote object or the remote object still has calls in progress. If the force parameter is false, the object is only unexported if there are no pending or in progress calls to the object.

Parameters:

obj - the remote object to be unexported

force - if true, unexports the object even if there are pending or in-progress calls; if false, only unexports the object if there are no pending or in-progress calls

Returns:

true if operation is successful, false otherwise

Throws:

NoSuchObjectException - if the remote object is not currently exported

Since:

1.2