001/* RemoteObjectInvocationHandler.java -- RMI stub replacement.
002 Copyright (C) 2005 Free Software Foundation, Inc.
003
004 This file is part of GNU Classpath.
005
006 GNU Classpath is free software; you can redistribute it and/or modify
007 it under the terms of the GNU General Public License as published by
008 the Free Software Foundation; either version 2, or (at your option)
009 any later version.
010
011 GNU Classpath is distributed in the hope that it will be useful, but
012 WITHOUT ANY WARRANTY; without even the implied warranty of
013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014 General Public License for more details.
015
016 You should have received a copy of the GNU General Public License
017 along with GNU Classpath; see the file COPYING.  If not, write to the
018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019 02110-1301 USA.
020
021 Linking this library statically or dynamically with other modules is
022 making a combined work based on this library.  Thus, the terms and
023 conditions of the GNU General Public License cover the whole
024 combination.
025
026 As a special exception, the copyright holders of this library give you
027 permission to link this library with independent modules to produce an
028 executable, regardless of the license terms of these independent
029 modules, and to copy and distribute the resulting executable under
030 terms of your choice, provided that you also meet, for each linked
031 independent module, the terms and conditions of the license of that
032 module.  An independent module is a module which is not derived from
033 or based on this library.  If you modify this library, you may extend
034 this exception to your version of the library, but you are not
035 obligated to do so.  If you do not wish to do so, delete this
036 exception statement from your version. */
037
038
039package java.rmi.server;
040
041import gnu.java.rmi.server.RMIHashes;
042
043import java.io.Serializable;
044import java.lang.reflect.InvocationHandler;
045import java.lang.reflect.Method;
046import java.lang.reflect.Proxy;
047import java.rmi.Remote;
048import java.rmi.RemoteException;
049import java.rmi.UnexpectedException;
050import java.rmi.registry.Registry;
051import java.rmi.server.RemoteObject;
052import java.rmi.server.RemoteRef;
053import java.rmi.server.UnicastRemoteObject;
054import java.util.Hashtable;
055
056/**
057 * Together with dynamic proxy instance, this class replaces the generated RMI
058 * stub (*_Stub) classes that (following 1.5 specification) should be no longer
059 * required. It is unusual to use the instances of this class directly in the
060 * user program. Such instances are automatically created and returned by
061 * {@link Registry} or {@link UnicastRemoteObject} methods if the remote
062 * reference is known but the corresponding stub class is not accessible.
063 * 
064 * @see Registry#lookup
065 *
066 * @author Audrius Meskauskas (AudriusA@Bioinformatics.org)
067 */
068public class RemoteObjectInvocationHandler extends RemoteObject implements
069    InvocationHandler, Remote, Serializable
070{
071  /**
072   * Use the jdk 1.5 SUID for interoperability.
073   */
074  static final long serialVersionUID = 2L;
075  
076  /**
077   * The RMI method hash codes, computed once as described in the section 8.3
078   * of the Java Remote Method Invocation (RMI) Specification.
079   */
080  static Hashtable methodHashCodes = new Hashtable();
081  
082  /**
083   * The empty class array to define parameters of .hashCode and .toString.
084   */
085  static final Class[] noArgsC = new Class[0];
086  
087  /**
088   * The class array to define parameters of .equals
089   */
090  static final Class[] anObjectC = new Class[] { Object.class };
091  
092  /**
093   * The empty object array to replace null when no args are passed.
094   */
095  static final Object[] noArgs = new Object[0];
096  
097  /**
098   * Construct the remote invocation handler that forwards calls to the given
099   * remote object.
100   * 
101   * @param reference the reference to the remote object where the method
102   * calls should be forwarded.
103   */
104  public RemoteObjectInvocationHandler(RemoteRef reference)
105  {
106    super(reference);
107  }
108
109  /**
110   * Invoke the remote method. When the known method is invoked on a created RMI
111   * stub proxy class, the call is delivered to this method and then transferred
112   * to the {@link RemoteRef#invoke(Remote, Method, Object[], long)} of the
113   * remote reference that was passed in constructor. The methods are handled as
114   * following:
115   * <ul>
116   * <li> The toString() method is delegated to the passed proxy instance.</li>
117   * <li>The .equals method only returns true if the passed object is an
118   * instance of proxy class and its invocation handler is equal to this
119   * invocation handles.</li>
120   * <li>The .hashCode returns the hashCode of this invocation handler (if the.</li>
121   * <li>All other methods are converted to remote calls and forwarded to the
122   * remote reference. </li>
123   * </ul>
124   * 
125   * @param proxyInstance
126   *          the instance of the proxy stub
127   * @param method
128   *          the method being invoked
129   * @param parameters
130   *          the method parameters
131   * @return the method return value, returned by RemoteRef.invoke
132   * @throws IllegalAccessException
133   *           if the passed proxy instance does not implement Remote interface.
134   * @throws UnexpectedException
135   *           if remote call throws some exception, not listed in the
136   *           <code>throws</code> clause of the method being called.
137   * @throws Throwable
138   *           that is thrown by remote call, if that exception is listend in
139   *           the <code>throws</code> clause of the method being called.
140   */
141  public Object invoke(Object proxyInstance, Method method, Object[] parameters)
142      throws Throwable
143  {
144    if (!(proxyInstance instanceof Remote))
145      {
146        String name = proxyInstance == null ? "null"
147                                           : proxyInstance.getClass().getName();
148        throw new IllegalAccessException(name + " does not implement "
149                                         + Remote.class.getName());
150      }
151    
152    if (parameters == null)
153      parameters = noArgs;
154
155    String name = method.getName();
156    switch (name.charAt(0))
157      {
158      case 'e':
159        if (parameters.length == 1 && name.equals("equals")
160            && method.getParameterTypes()[0].equals(Object.class))
161          {
162            if (parameters[0] instanceof Proxy)
163              {
164                Object handler = Proxy.getInvocationHandler(parameters[0]);
165                if (handler == null)
166                  return Boolean.FALSE;
167                else
168                  return handler.equals(this) ? Boolean.TRUE : Boolean.FALSE;
169              }
170            else
171              return Boolean.FALSE;
172          }
173        break;
174      case 'h':
175        if (parameters.length == 0 && name.equals("hashCode"))
176          {
177            int hashC = Proxy.getInvocationHandler(proxyInstance).hashCode();
178            return new Integer(hashC);
179          }
180        break;
181      case 't':
182        if (parameters.length == 0 && name.equals("toString"))
183          return "Proxy stub:"+ref.remoteToString();
184        break;
185      default:
186        break;
187      }
188
189    Long hash = (Long) methodHashCodes.get(method);
190    if (hash == null)
191      {
192        hash = new Long(RMIHashes.getMethodHash(method));
193        methodHashCodes.put(method, hash);
194      }
195
196    try
197      {
198        return getRef().invoke((Remote) proxyInstance, method, parameters,
199                               hash.longValue());
200      }
201    catch (RuntimeException exception)
202      {
203        // RuntimeException is always supported.
204        throw exception;
205      }
206    catch (RemoteException exception)
207      {
208        // All remote methods can throw RemoteException.
209        throw exception;
210      }
211    catch (Error exception)
212      {
213        throw exception;
214      }
215    catch (Exception exception)
216      {
217        Class[] exceptions = method.getExceptionTypes();
218        Class exceptionClass = exception.getClass();
219
220        for (int i = 0; i < exceptions.length; i++)
221          {
222            if (exceptions[i].equals(exceptionClass))
223              throw exception;
224          }
225        throw new UnexpectedException(method.getName(), exception);
226      }
227  }
228
229}