PortableRemoteObject.java

/* PortableRemoteObject.java --
   Copyright (C) 2004, 2004, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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02110-1301 USA.

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permission to link this library with independent modules to produce an
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package javax.rmi;

import gnu.javax.rmi.CORBA.DelegateFactory;

import org.omg.CORBA.BAD_PARAM;
import org.omg.CORBA.ORB;
import org.omg.CORBA.portable.ObjectImpl;
import org.omg.PortableServer.POA;
import org.omg.PortableServer.Servant;

import java.rmi.NoSuchObjectException;
import java.rmi.Remote;
import java.rmi.RemoteException;

import javax.rmi.CORBA.PortableRemoteObjectDelegate;
import javax.rmi.CORBA.Stub;
import javax.rmi.CORBA.Tie;
import javax.rmi.CORBA.Util;

/**
 * <p>
 * An utility class for RMI/IDL server side object implementations. Server side
 * implementation objects may inherit from this class, but this is not
 * mandatory, as the needed methds are static. Server side implementations may
 * choose to inherit from {@link ObjectImpl} or {@link Servant} instead.
 * </p>
 * <p>
 * The functionality of methods in this class is forwarded to the enclosed
 * PortableRemoteObjectDelegate. This delegate can be altered by setting the
 * system property "javax.rmi.CORBA.PortableRemoteObjectClass" to the name of
 * the alternative class that must implement
 * {@link PortableRemoteObjectDelegate}.
 * </p>
 *
 * @author Audrius Meskauskas (AudriusA@Bioinformatics.org)
 */
public class PortableRemoteObject
{
  /**
   * A delegate where the functionality is forwarded.
   */
  static PortableRemoteObjectDelegate delegate = (PortableRemoteObjectDelegate) DelegateFactory.getInstance(DelegateFactory.PORTABLE_REMOTE_OBJECT);

  /**
   * The protected constructor calls {@link exportObject} (this).
   *
   * @throws RemoteException if the exportObject(this) throws one.
   */
  protected PortableRemoteObject()
    throws RemoteException
  {
    exportObject((Remote) this);
  }

  /**
   * <p>
   * Makes the remote object <code>a_target</code> ready for remote
   * communication using the same communications runtime as for the passed
   * <code>a_source</code> parameter. The a_target is connected to the same
   * ORB (and, if applicable, to the same {@link POA}) as the a_source.
   *
   * @param target the target to connect to ORB, must be an instance of either
   * {@link ObjectImpl} (Stubs and old-style ties) or {@link Tie}.
   *
   * @param source the object, providing the connection information, must be
   * an instance of either {@link ObjectImpl} (Stubs and old-style ties) or
   * {@link Servant} (the next-generation Ties supporting {@link POA}).
   *
   * @throws RemoteException if the target is already connected to another ORB.
   */
  public static void connect(Remote target, Remote source)
    throws RemoteException
  {
    delegate.connect(target, source);
  }

  /**
   * <p>
   * Makes a server object ready for remote calls. The subclasses of
   * PortableRemoteObject do not need to call this method, as it is called by
   * the constructor.
   * </p>
   * <p>
   * This method only creates a tie object and caches it for future usage. The
   * created tie does not have a delegate or an ORB associated.
   * </p>
   *
   * @param object the object to export.
   *
   * @throws RemoteException if export fails due any reason.
   */
  public static void exportObject(Remote object)
    throws RemoteException
  {
    delegate.exportObject(object);
  }

  /**
   * Narrows the passed object to conform to the given interface or IDL type. In
   * RMI-IIOP, this method replaces the narrow(org.omg.CORBA.Object) method that
   * was present in the CORBA Helpers. This method frequently returns different
   * instance and cannot be replaced by the direct cast. The typical narrowing
   * cases (all supported by GNU Classpath) are:
   * <ul>
   * <li>A CORBA object (for instance, returned by the
   * {@link ORB#string_to_object} or from the naming service) can be narrowed
   * into interface, derived from Remote. The method will try to locate an
   * appropriate {@link Stub} by the name pattern (_*_Stub). If the object being
   * narrowed is connected to an ORB, the returned instance will inherit that
   * connection, representing the same remote (or local) object, but now with
   * the possibility to invoke remote methods. </li>
   * <li>A CORBA object may be directly narrowed into the appropriate
   * {@link Stub} class, if it is and passed as a second parameter. This allows
   * to use non-standard stubs without parameterless constructors.</li>
   * <li>Any two classes, derived from the {@link ObjectImpl} (may be Stub's)
   * can be narrowed one into another (a delegate is transferred). </li>
   * <li>An implementation of Remote can be narrowed into {@link Tie} that can
   * later connected to an ORB, making the methods accessible remotely. The
   * Remote being narrowed normally provides a local implementation, but you can
   * also narrow remote Stub, creating "forwarding Tie".</li>
   * <li>null is narrowed into null regardless of the second parameter.</li>
   * <li>A {@link Tie} can be narrowed into Remote, representing the
   * implementation for this Tie (if one is set).</li>
   * </ul>
   *
   * @param object the object like CORBA Object, Stub or Remote that must be
   * narrowed to the given interface.
   *
   * @param narrowToInstaceOf the class of the interface to that the object must
   * be narrowed.
   *
   * @return On success, an object of type narrowTo or null, if narrowFrom =
   * null.
   *
   * @throws ClassCastException if no narrowing is possible.
   */
  public static Object narrow(Object object, Class narrowToInstaceOf)
    throws ClassCastException
  {
    return delegate.narrow(object, narrowToInstaceOf);
  }

  /**
   * <p>
   * Takes a server implementation object (name pattern *imp) and returns a stub
   * object that can be used to access that server object (target), name
   * (pattern _*_Stub).
   *
   * The returned stub is not connected to any ORB and must be explicitly
   * connected using {@link #connect}.
   * </p>
   * <p>
   * The method signature prevents it from returning stubs that does not
   * implement Remote (ClassCastException will be thrown).
   * </p>
   *
   * @param target a server side object implementation.
   * @return a stub object that can be used to access that server object.
   *
   * @throws NoSuchObjectException if a stub class cannot be located by supposed
   * name pattern, or an instance of stub fails to be instantiated.
   *
   * @throws ClassCastException if the stub class can be located, but it does
   * not inherit from Remote.
   *
   * @throws BAD_PARAM if the name of the passed class does not match the
   * implementation name pattern (does not end by 'Impl').
   */
  public static Remote toStub(Remote targetImpl)
    throws NoSuchObjectException
  {
    return delegate.toStub(targetImpl);
  }

  /**
   * Deregister a currently exported server object from the ORB runtimes. The
   * object to becomes available for garbage collection. This is usually
   * impemented via {@link Util#unexportObject}
   *
   * @param object the object to unexport.
   *
   * @throws NoSuchObjectException if the passed object is not currently
   * exported.
   */
  public static void unexportObject(Remote object)
    throws NoSuchObjectException
  {
    delegate.unexportObject(object);
  }
}