J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1996-2006 Sun Microsystems, Inc. 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. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | package java.rmi.server; |
| 26 | |
| 27 | import java.io.DataInput; |
| 28 | import java.io.DataOutput; |
| 29 | import java.io.IOException; |
| 30 | import java.io.ObjectInput; |
| 31 | import java.io.ObjectOutput; |
| 32 | import java.io.Serializable; |
| 33 | import java.security.AccessController; |
| 34 | import java.security.SecureRandom; |
| 35 | import java.util.concurrent.atomic.AtomicLong; |
| 36 | import sun.security.action.GetPropertyAction; |
| 37 | |
| 38 | /** |
| 39 | * An <code>ObjID</code> is used to identify a remote object exported |
| 40 | * to an RMI runtime. When a remote object is exported, it is assigned |
| 41 | * an object identifier either implicitly or explicitly, depending on |
| 42 | * the API used to export. |
| 43 | * |
| 44 | * <p>The {@link #ObjID()} constructor can be used to generate a unique |
| 45 | * object identifier. Such an <code>ObjID</code> is unique over time |
| 46 | * with respect to the host it is generated on. |
| 47 | * |
| 48 | * The {@link #ObjID(int)} constructor can be used to create a |
| 49 | * "well-known" object identifier. The scope of a well-known |
| 50 | * <code>ObjID</code> depends on the RMI runtime it is exported to. |
| 51 | * |
| 52 | * <p>An <code>ObjID</code> instance contains an object number (of type |
| 53 | * <code>long</code>) and an address space identifier (of type |
| 54 | * {@link UID}). In a unique <code>ObjID</code>, the address space |
| 55 | * identifier is unique with respect to a given host over time. In a |
| 56 | * well-known <code>ObjID</code>, the address space identifier is |
| 57 | * equivalent to one returned by invoking the {@link UID#UID(short)} |
| 58 | * constructor with the value zero. |
| 59 | * |
| 60 | * <p>If the system property <code>java.rmi.server.randomIDs</code> |
| 61 | * is defined to equal the string <code>"true"</code> (case insensitive), |
| 62 | * then the {@link #ObjID()} constructor will use a cryptographically |
| 63 | * strong random number generator to choose the object number of the |
| 64 | * returned <code>ObjID</code>. |
| 65 | * |
| 66 | * @author Ann Wollrath |
| 67 | * @author Peter Jones |
| 68 | * @since JDK1.1 |
| 69 | */ |
| 70 | public final class ObjID implements Serializable { |
| 71 | |
| 72 | /** Object number for well-known <code>ObjID</code> of the registry. */ |
| 73 | public static final int REGISTRY_ID = 0; |
| 74 | |
| 75 | /** Object number for well-known <code>ObjID</code> of the activator. */ |
| 76 | public static final int ACTIVATOR_ID = 1; |
| 77 | |
| 78 | /** |
| 79 | * Object number for well-known <code>ObjID</code> of |
| 80 | * the distributed garbage collector. |
| 81 | */ |
| 82 | public static final int DGC_ID = 2; |
| 83 | |
| 84 | /** indicate compatibility with JDK 1.1.x version of class */ |
| 85 | private static final long serialVersionUID = -6386392263968365220L; |
| 86 | |
| 87 | private static final AtomicLong nextObjNum = new AtomicLong(0); |
| 88 | private static final UID mySpace = new UID(); |
| 89 | private static final SecureRandom secureRandom = new SecureRandom(); |
| 90 | |
| 91 | /** |
| 92 | * @serial object number |
| 93 | * @see #hashCode |
| 94 | */ |
| 95 | private final long objNum; |
| 96 | |
| 97 | /** |
| 98 | * @serial address space identifier (unique to host over time) |
| 99 | */ |
| 100 | private final UID space; |
| 101 | |
| 102 | /** |
| 103 | * Generates a unique object identifier. |
| 104 | * |
| 105 | * <p>If the system property <code>java.rmi.server.randomIDs</code> |
| 106 | * is defined to equal the string <code>"true"</code> (case insensitive), |
| 107 | * then this constructor will use a cryptographically |
| 108 | * strong random number generator to choose the object number of the |
| 109 | * returned <code>ObjID</code>. |
| 110 | */ |
| 111 | public ObjID() { |
| 112 | /* |
| 113 | * If generating random object numbers, create a new UID to |
| 114 | * ensure uniqueness; otherwise, use a shared UID because |
| 115 | * sequential object numbers already ensure uniqueness. |
| 116 | */ |
| 117 | if (useRandomIDs()) { |
| 118 | space = new UID(); |
| 119 | objNum = secureRandom.nextLong(); |
| 120 | } else { |
| 121 | space = mySpace; |
| 122 | objNum = nextObjNum.getAndIncrement(); |
| 123 | } |
| 124 | } |
| 125 | |
| 126 | /** |
| 127 | * Creates a "well-known" object identifier. |
| 128 | * |
| 129 | * <p>An <code>ObjID</code> created via this constructor will not |
| 130 | * clash with any <code>ObjID</code>s generated via the no-arg |
| 131 | * constructor. |
| 132 | * |
| 133 | * @param objNum object number for well-known object identifier |
| 134 | */ |
| 135 | public ObjID(int objNum) { |
| 136 | space = new UID((short) 0); |
| 137 | this.objNum = objNum; |
| 138 | } |
| 139 | |
| 140 | /** |
| 141 | * Constructs an object identifier given data read from a stream. |
| 142 | */ |
| 143 | private ObjID(long objNum, UID space) { |
| 144 | this.objNum = objNum; |
| 145 | this.space = space; |
| 146 | } |
| 147 | |
| 148 | /** |
| 149 | * Marshals a binary representation of this <code>ObjID</code> to |
| 150 | * an <code>ObjectOutput</code> instance. |
| 151 | * |
| 152 | * <p>Specifically, this method first invokes the given stream's |
| 153 | * {@link ObjectOutput#writeLong(long)} method with this object |
| 154 | * identifier's object number, and then it writes its address |
| 155 | * space identifier by invoking its {@link UID#write(DataOutput)} |
| 156 | * method with the stream. |
| 157 | * |
| 158 | * @param out the <code>ObjectOutput</code> instance to write |
| 159 | * this <code>ObjID</code> to |
| 160 | * |
| 161 | * @throws IOException if an I/O error occurs while performing |
| 162 | * this operation |
| 163 | */ |
| 164 | public void write(ObjectOutput out) throws IOException { |
| 165 | out.writeLong(objNum); |
| 166 | space.write(out); |
| 167 | } |
| 168 | |
| 169 | /** |
| 170 | * Constructs and returns a new <code>ObjID</code> instance by |
| 171 | * unmarshalling a binary representation from an |
| 172 | * <code>ObjectInput</code> instance. |
| 173 | * |
| 174 | * <p>Specifically, this method first invokes the given stream's |
| 175 | * {@link ObjectInput#readLong()} method to read an object number, |
| 176 | * then it invokes {@link UID#read(DataInput)} with the |
| 177 | * stream to read an address space identifier, and then it |
| 178 | * creates and returns a new <code>ObjID</code> instance that |
| 179 | * contains the object number and address space identifier that |
| 180 | * were read from the stream. |
| 181 | * |
| 182 | * @param in the <code>ObjectInput</code> instance to read |
| 183 | * <code>ObjID</code> from |
| 184 | * |
| 185 | * @return unmarshalled <code>ObjID</code> instance |
| 186 | * |
| 187 | * @throws IOException if an I/O error occurs while performing |
| 188 | * this operation |
| 189 | */ |
| 190 | public static ObjID read(ObjectInput in) throws IOException { |
| 191 | long num = in.readLong(); |
| 192 | UID space = UID.read(in); |
| 193 | return new ObjID(num, space); |
| 194 | } |
| 195 | |
| 196 | /** |
| 197 | * Returns the hash code value for this object identifier, the |
| 198 | * object number. |
| 199 | * |
| 200 | * @return the hash code value for this object identifier |
| 201 | */ |
| 202 | public int hashCode() { |
| 203 | return (int) objNum; |
| 204 | } |
| 205 | |
| 206 | /** |
| 207 | * Compares the specified object with this <code>ObjID</code> for |
| 208 | * equality. |
| 209 | * |
| 210 | * This method returns <code>true</code> if and only if the |
| 211 | * specified object is an <code>ObjID</code> instance with the same |
| 212 | * object number and address space identifier as this one. |
| 213 | * |
| 214 | * @param obj the object to compare this <code>ObjID</code> to |
| 215 | * |
| 216 | * @return <code>true</code> if the given object is equivalent to |
| 217 | * this one, and <code>false</code> otherwise |
| 218 | */ |
| 219 | public boolean equals(Object obj) { |
| 220 | if (obj instanceof ObjID) { |
| 221 | ObjID id = (ObjID) obj; |
| 222 | return objNum == id.objNum && space.equals(id.space); |
| 223 | } else { |
| 224 | return false; |
| 225 | } |
| 226 | } |
| 227 | |
| 228 | /** |
| 229 | * Returns a string representation of this object identifier. |
| 230 | * |
| 231 | * @return a string representation of this object identifier |
| 232 | */ |
| 233 | /* |
| 234 | * The address space identifier is only included in the string |
| 235 | * representation if it does not denote the local address space |
| 236 | * (or if the randomIDs property was set). |
| 237 | */ |
| 238 | public String toString() { |
| 239 | return "[" + (space.equals(mySpace) ? "" : space + ", ") + |
| 240 | objNum + "]"; |
| 241 | } |
| 242 | |
| 243 | private static boolean useRandomIDs() { |
| 244 | String value = AccessController.doPrivileged( |
| 245 | new GetPropertyAction("java.rmi.server.randomIDs")); |
| 246 | return value == null ? true : Boolean.parseBoolean(value); |
| 247 | } |
| 248 | } |