1 /*
   2  * Copyright (c) 1996, 2003, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.rmi.server;
  27 
  28 import java.rmi.Remote;
  29 import java.rmi.NoSuchObjectException;
  30 import java.lang.reflect.Proxy;
  31 import sun.rmi.server.Util;
  32 
  33 /**
  34  * The <code>RemoteObject</code> class implements the
  35  * <code>java.lang.Object</code> behavior for remote objects.
  36  * <code>RemoteObject</code> provides the remote semantics of Object by
  37  * implementing methods for hashCode, equals, and toString.
  38  *
  39  * @author      Ann Wollrath
  40  * @author      Laird Dornin
  41  * @author      Peter Jones
  42  * @since       JDK1.1
  43  */
  44 public abstract class RemoteObject implements Remote, java.io.Serializable {
  45 
  46     /** The object's remote reference. */
  47     transient protected RemoteRef ref;
  48 
  49     /** indicate compatibility with JDK 1.1.x version of class */
  50     private static final long serialVersionUID = -3215090123894869218L;
  51 
  52     /**
  53      * Creates a remote object.
  54      */
  55     protected RemoteObject() {
  56         ref = null;
  57     }
  58 
  59     /**
  60      * Creates a remote object, initialized with the specified remote
  61      * reference.
  62      * @param newref remote reference
  63      */
  64     protected RemoteObject(RemoteRef newref) {
  65         ref = newref;
  66     }
  67 
  68     /**
  69      * Returns the remote reference for the remote object.
  70      *
  71      * <p>Note: The object returned from this method may be an instance of
  72      * an implementation-specific class.  The <code>RemoteObject</code>
  73      * class ensures serialization portability of its instances' remote
  74      * references through the behavior of its custom
  75      * <code>writeObject</code> and <code>readObject</code> methods.  An
  76      * instance of <code>RemoteRef</code> should not be serialized outside
  77      * of its <code>RemoteObject</code> wrapper instance or the result may
  78      * be unportable.
  79      *
  80      * @return remote reference for the remote object
  81      * @since 1.2
  82      */
  83     public RemoteRef getRef() {
  84         return ref;
  85     }
  86 
  87     /**
  88      * Returns the stub for the remote object <code>obj</code> passed
  89      * as a parameter. This operation is only valid <i>after</i>
  90      * the object has been exported.
  91      * @param obj the remote object whose stub is needed
  92      * @return the stub for the remote object, <code>obj</code>.
  93      * @exception NoSuchObjectException if the stub for the
  94      * remote object could not be found.
  95      * @since 1.2
  96      */
  97     public static Remote toStub(Remote obj) throws NoSuchObjectException {
  98         if (obj instanceof RemoteStub ||
  99             (obj != null &&
 100              Proxy.isProxyClass(obj.getClass()) &&
 101              Proxy.getInvocationHandler(obj) instanceof
 102              RemoteObjectInvocationHandler))
 103         {
 104             return obj;
 105         } else {
 106             return sun.rmi.transport.ObjectTable.getStub(obj);
 107         }
 108     }
 109 
 110     /**
 111      * Returns a hashcode for a remote object.  Two remote object stubs
 112      * that refer to the same remote object will have the same hash code
 113      * (in order to support remote objects as keys in hash tables).
 114      *
 115      * @see             java.util.Hashtable
 116      */
 117     public int hashCode() {
 118         return (ref == null) ? super.hashCode() : ref.remoteHashCode();
 119     }
 120 
 121     /**
 122      * Compares two remote objects for equality.
 123      * Returns a boolean that indicates whether this remote object is
 124      * equivalent to the specified Object. This method is used when a
 125      * remote object is stored in a hashtable.
 126      * If the specified Object is not itself an instance of RemoteObject,
 127      * then this method delegates by returning the result of invoking the
 128      * <code>equals</code> method of its parameter with this remote object
 129      * as the argument.
 130      * @param   obj     the Object to compare with
 131      * @return  true if these Objects are equal; false otherwise.
 132      * @see             java.util.Hashtable
 133      */
 134     public boolean equals(Object obj) {
 135         if (obj instanceof RemoteObject) {
 136             if (ref == null) {
 137                 return obj == this;
 138             } else {
 139                 return ref.remoteEquals(((RemoteObject)obj).ref);
 140             }
 141         } else if (obj != null) {
 142             /*
 143              * Fix for 4099660: if object is not an instance of RemoteObject,
 144              * use the result of its equals method, to support symmetry is a
 145              * remote object implementation class that does not extend
 146              * RemoteObject wishes to support equality with its stub objects.
 147              */
 148             return obj.equals(this);
 149         } else {
 150             return false;
 151         }
 152     }
 153 
 154     /**
 155      * Returns a String that represents the value of this remote object.
 156      */
 157     public String toString() {
 158         String classname = Util.getUnqualifiedName(getClass());
 159         return (ref == null) ? classname :
 160             classname + "[" + ref.remoteToString() + "]";
 161     }
 162 
 163     /**
 164      * <code>writeObject</code> for custom serialization.
 165      *
 166      * <p>This method writes this object's serialized form for this class
 167      * as follows:
 168      *
 169      * <p>The {@link RemoteRef#getRefClass(java.io.ObjectOutput) getRefClass}
 170      * method is invoked on this object's <code>ref</code> field
 171      * to obtain its external ref type name.
 172      * If the value returned by <code>getRefClass</code> was
 173      * a non-<code>null</code> string of length greater than zero,
 174      * the <code>writeUTF</code> method is invoked on <code>out</code>
 175      * with the value returned by <code>getRefClass</code>, and then
 176      * the <code>writeExternal</code> method is invoked on
 177      * this object's <code>ref</code> field passing <code>out</code>
 178      * as the argument; otherwise,
 179      * the <code>writeUTF</code> method is invoked on <code>out</code>
 180      * with a zero-length string (<code>""</code>), and then
 181      * the <code>writeObject</code> method is invoked on <code>out</code>
 182      * passing this object's <code>ref</code> field as the argument.
 183      *
 184      * @serialData
 185      *
 186      * The serialized data for this class comprises a string (written with
 187      * <code>ObjectOutput.writeUTF</code>) that is either the external
 188      * ref type name of the contained <code>RemoteRef</code> instance
 189      * (the <code>ref</code> field) or a zero-length string, followed by
 190      * either the external form of the <code>ref</code> field as written by
 191      * its <code>writeExternal</code> method if the string was of non-zero
 192      * length, or the serialized form of the <code>ref</code> field as
 193      * written by passing it to the serialization stream's
 194      * <code>writeObject</code> if the string was of zero length.
 195      *
 196      * <p>If this object is an instance of
 197      * {@link RemoteStub} or {@link RemoteObjectInvocationHandler}
 198      * that was returned from any of
 199      * the <code>UnicastRemoteObject.exportObject</code> methods
 200      * and custom socket factories are not used,
 201      * the external ref type name is <code>"UnicastRef"</code>.
 202      *
 203      * If this object is an instance of
 204      * <code>RemoteStub</code> or <code>RemoteObjectInvocationHandler</code>
 205      * that was returned from any of
 206      * the <code>UnicastRemoteObject.exportObject</code> methods
 207      * and custom socket factories are used,
 208      * the external ref type name is <code>"UnicastRef2"</code>.
 209      *
 210      * If this object is an instance of
 211      * <code>RemoteStub</code> or <code>RemoteObjectInvocationHandler</code>
 212      * that was returned from any of
 213      * the <code>java.rmi.activation.Activatable.exportObject</code> methods,
 214      * the external ref type name is <code>"ActivatableRef"</code>.
 215      *
 216      * If this object is an instance of
 217      * <code>RemoteStub</code> or <code>RemoteObjectInvocationHandler</code>
 218      * that was returned from
 219      * the <code>RemoteObject.toStub</code> method (and the argument passed
 220      * to <code>toStub</code> was not itself a <code>RemoteStub</code>),
 221      * the external ref type name is a function of how the remote object
 222      * passed to <code>toStub</code> was exported, as described above.
 223      *
 224      * If this object is an instance of
 225      * <code>RemoteStub</code> or <code>RemoteObjectInvocationHandler</code>
 226      * that was originally created via deserialization,
 227      * the external ref type name is the same as that which was read
 228      * when this object was deserialized.
 229      *
 230      * <p>If this object is an instance of
 231      * <code>java.rmi.server.UnicastRemoteObject</code> that does not
 232      * use custom socket factories,
 233      * the external ref type name is <code>"UnicastServerRef"</code>.
 234      *
 235      * If this object is an instance of
 236      * <code>UnicastRemoteObject</code> that does
 237      * use custom socket factories,
 238      * the external ref type name is <code>"UnicastServerRef2"</code>.
 239      *
 240      * <p>Following is the data that must be written by the
 241      * <code>writeExternal</code> method and read by the
 242      * <code>readExternal</code> method of <code>RemoteRef</code>
 243      * implementation classes that correspond to the each of the
 244      * defined external ref type names:
 245      *
 246      * <p>For <code>"UnicastRef"</code>:
 247      *
 248      * <ul>
 249      *
 250      * <li>the hostname of the referenced remote object,
 251      * written by {@link java.io.ObjectOutput#writeUTF(String)}
 252      *
 253      * <li>the port of the referenced remote object,
 254      * written by {@link java.io.ObjectOutput#writeInt(int)}
 255      *
 256      * <li>the data written as a result of calling
 257      * {link java.rmi.server.ObjID#write(java.io.ObjectOutput)}
 258      * on the <code>ObjID</code> instance contained in the reference
 259      *
 260      * <li>the boolean value <code>false</code>,
 261      * written by {@link java.io.ObjectOutput#writeBoolean(boolean)}
 262      *
 263      * </ul>
 264      *
 265      * <p>For <code>"UnicastRef2"</code> with a
 266      * <code>null</code> client socket factory:
 267      *
 268      * <ul>
 269      *
 270      * <li>the byte value <code>0x00</code>
 271      * (indicating <code>null</code> client socket factory),
 272      * written by {@link java.io.ObjectOutput#writeByte(int)}
 273      *
 274      * <li>the hostname of the referenced remote object,
 275      * written by {@link java.io.ObjectOutput#writeUTF(String)}
 276      *
 277      * <li>the port of the referenced remote object,
 278      * written by {@link java.io.ObjectOutput#writeInt(int)}
 279      *
 280      * <li>the data written as a result of calling
 281      * {link java.rmi.server.ObjID#write(java.io.ObjectOutput)}
 282      * on the <code>ObjID</code> instance contained in the reference
 283      *
 284      * <li>the boolean value <code>false</code>,
 285      * written by {@link java.io.ObjectOutput#writeBoolean(boolean)}
 286      *
 287      * </ul>
 288      *
 289      * <p>For <code>"UnicastRef2"</code> with a
 290      * non-<code>null</code> client socket factory:
 291      *
 292      * <ul>
 293      *
 294      * <li>the byte value <code>0x01</code>
 295      * (indicating non-<code>null</code> client socket factory),
 296      * written by {@link java.io.ObjectOutput#writeByte(int)}
 297      *
 298      * <li>the hostname of the referenced remote object,
 299      * written by {@link java.io.ObjectOutput#writeUTF(String)}
 300      *
 301      * <li>the port of the referenced remote object,
 302      * written by {@link java.io.ObjectOutput#writeInt(int)}
 303      *
 304      * <li>a client socket factory (object of type
 305      * <code>java.rmi.server.RMIClientSocketFactory</code>),
 306      * written by passing it to an invocation of
 307      * <code>writeObject</code> on the stream instance
 308      *
 309      * <li>the data written as a result of calling
 310      * {link java.rmi.server.ObjID#write(java.io.ObjectOutput)}
 311      * on the <code>ObjID</code> instance contained in the reference
 312      *
 313      * <li>the boolean value <code>false</code>,
 314      * written by {@link java.io.ObjectOutput#writeBoolean(boolean)}
 315      *
 316      * </ul>
 317      *
 318      * <p>For <code>"ActivatableRef"</code> with a
 319      * <code>null</code> nested remote reference:
 320      *
 321      * <ul>
 322      *
 323      * <li>an instance of
 324      * <code>java.rmi.activation.ActivationID</code>,
 325      * written by passing it to an invocation of
 326      * <code>writeObject</code> on the stream instance
 327      *
 328      * <li>a zero-length string (<code>""</code>),
 329      * written by {@link java.io.ObjectOutput#writeUTF(String)}
 330      *
 331      * </ul>
 332      *
 333      * <p>For <code>"ActivatableRef"</code> with a
 334      * non-<code>null</code> nested remote reference:
 335      *
 336      * <ul>
 337      *
 338      * <li>an instance of
 339      * <code>java.rmi.activation.ActivationID</code>,
 340      * written by passing it to an invocation of
 341      * <code>writeObject</code> on the stream instance
 342      *
 343      * <li>the external ref type name of the nested remote reference,
 344      * which must be <code>"UnicastRef2"</code>,
 345      * written by {@link java.io.ObjectOutput#writeUTF(String)}
 346      *
 347      * <li>the external form of the nested remote reference,
 348      * written by invoking its <code>writeExternal</code> method
 349      * with the stream instance
 350      * (see the description of the external form for
 351      * <code>"UnicastRef2"</code> above)
 352      *
 353      * </ul>
 354      *
 355      * <p>For <code>"UnicastServerRef"</code> and
 356      * <code>"UnicastServerRef2"</code>, no data is written by the
 357      * <code>writeExternal</code> method or read by the
 358      * <code>readExternal</code> method.
 359      */
 360     private void writeObject(java.io.ObjectOutputStream out)
 361         throws java.io.IOException, java.lang.ClassNotFoundException
 362     {
 363         if (ref == null) {
 364             throw new java.rmi.MarshalException("Invalid remote object");
 365         } else {
 366             String refClassName = ref.getRefClass(out);
 367             if (refClassName == null || refClassName.length() == 0) {
 368                 /*
 369                  * No reference class name specified, so serialize
 370                  * remote reference.
 371                  */
 372                 out.writeUTF("");
 373                 out.writeObject(ref);
 374             } else {
 375                 /*
 376                  * Built-in reference class specified, so delegate
 377                  * to reference to write out its external form.
 378                  */
 379                 out.writeUTF(refClassName);
 380                 ref.writeExternal(out);
 381             }
 382         }
 383     }
 384 
 385     /**
 386      * <code>readObject</code> for custom serialization.
 387      *
 388      * <p>This method reads this object's serialized form for this class
 389      * as follows:
 390      *
 391      * <p>The <code>readUTF</code> method is invoked on <code>in</code>
 392      * to read the external ref type name for the <code>RemoteRef</code>
 393      * instance to be filled in to this object's <code>ref</code> field.
 394      * If the string returned by <code>readUTF</code> has length zero,
 395      * the <code>readObject</code> method is invoked on <code>in</code>,
 396      * and than the value returned by <code>readObject</code> is cast to
 397      * <code>RemoteRef</code> and this object's <code>ref</code> field is
 398      * set to that value.
 399      * Otherwise, this object's <code>ref</code> field is set to a
 400      * <code>RemoteRef</code> instance that is created of an
 401      * implementation-specific class corresponding to the external ref
 402      * type name returned by <code>readUTF</code>, and then
 403      * the <code>readExternal</code> method is invoked on
 404      * this object's <code>ref</code> field.
 405      *
 406      * <p>If the external ref type name is
 407      * <code>"UnicastRef"</code>, <code>"UnicastServerRef"</code>,
 408      * <code>"UnicastRef2"</code>, <code>"UnicastServerRef2"</code>,
 409      * or <code>"ActivatableRef"</code>, a corresponding
 410      * implementation-specific class must be found, and its
 411      * <code>readExternal</code> method must read the serial data
 412      * for that external ref type name as specified to be written
 413      * in the <b>serialData</b> documentation for this class.
 414      * If the external ref type name is any other string (of non-zero
 415      * length), a <code>ClassNotFoundException</code> will be thrown,
 416      * unless the implementation provides an implementation-specific
 417      * class corresponding to that external ref type name, in which
 418      * case this object's <code>ref</code> field will be set to an
 419      * instance of that implementation-specific class.
 420      */
 421     private void readObject(java.io.ObjectInputStream in)
 422         throws java.io.IOException, java.lang.ClassNotFoundException
 423     {
 424         String refClassName = in.readUTF();
 425         if (refClassName == null || refClassName.length() == 0) {
 426             /*
 427              * No reference class name specified, so construct
 428              * remote reference from its serialized form.
 429              */
 430             ref = (RemoteRef) in.readObject();
 431         } else {
 432             /*
 433              * Built-in reference class specified, so delegate to
 434              * internal reference class to initialize its fields from
 435              * its external form.
 436              */
 437             String internalRefClassName =
 438                 RemoteRef.packagePrefix + "." + refClassName;
 439             Class<?> refClass = Class.forName(internalRefClassName);
 440             try {
 441                 ref = (RemoteRef) refClass.newInstance();
 442 
 443                 /*
 444                  * If this step fails, assume we found an internal
 445                  * class that is not meant to be a serializable ref
 446                  * type.
 447                  */
 448             } catch (InstantiationException e) {
 449                 throw new ClassNotFoundException(internalRefClassName, e);
 450             } catch (IllegalAccessException e) {
 451                 throw new ClassNotFoundException(internalRefClassName, e);
 452             } catch (ClassCastException e) {
 453                 throw new ClassNotFoundException(internalRefClassName, e);
 454             }
 455             ref.readExternal(in);
 456         }
 457     }
 458 }