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/* * @(#)ObjID.java 1.31 06/02/23 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.rmi.server; import java.io.DataInput; import java.io.DataOutput; import java.io.IOException; import java.io.ObjectInput; import java.io.ObjectOutput; import java.io.Serializable; import java.security.AccessController; import java.security.SecureRandom; import java.util.concurrent.atomic.AtomicLong; import sun.security.action.GetPropertyAction; /** * An <code>ObjID</code> is used to identify a remote object exported * to an RMI runtime. When a remote object is exported, it is assigned * an object identifier either implicitly or explicitly, depending on * the API used to export. * * <p>The {@link #ObjID()} constructor can be used to generate a unique * object identifier. Such an <code>ObjID</code> is unique over time * with respect to the host it is generated on. * * The {@link #ObjID(int)} constructor can be used to create a * "well-known" object identifier. The scope of a well-known * <code>ObjID</code> depends on the RMI runtime it is exported to. * * <p>An <code>ObjID</code> instance contains an object number (of type * <code>long</code>) and an address space identifier (of type * {@link UID}). In a unique <code>ObjID</code>, the address space * identifier is unique with respect to a given host over time. In a * well-known <code>ObjID</code>, the address space identifier is * equivalent to one returned by invoking the {@link UID#UID(short)} * constructor with the value zero. * * <p>If the system property <code>java.rmi.server.randomIDs</code> * is defined to equal the string <code>"true"</code> (case insensitive), * then the {@link #ObjID()} constructor will use a cryptographically * strong random number generator to choose the object number of the * returned <code>ObjID</code>. * * @author Ann Wollrath * @author Peter Jones * @version 1.31, 06/02/23 * @since JDK1.1 */ public final class ObjID implements Serializable { /** Object number for well-known <code>ObjID</code> of the registry. */ public static final int REGISTRY_ID = 0; /** Object number for well-known <code>ObjID</code> of the activator. */ public static final int ACTIVATOR_ID = 1; /** * Object number for well-known <code>ObjID</code> of * the distributed garbage collector. */ public static final int DGC_ID = 2; /** indicate compatibility with JDK 1.1.x version of class */ private static final long serialVersionUID = -6386392263968365220L; private static final AtomicLong nextObjNum = new AtomicLong(0); private static final UID mySpace = new UID(); private static final SecureRandom secureRandom = new SecureRandom(); /** * @serial object number * @see #hashCode */ private final long objNum; /** * @serial address space identifier (unique to host over time) */ private final UID space; /** * Generates a unique object identifier. * * <p>If the system property <code>java.rmi.server.randomIDs</code> * is defined to equal the string <code>"true"</code> (case insensitive), * then this constructor will use a cryptographically * strong random number generator to choose the object number of the * returned <code>ObjID</code>. */ public ObjID() { /* * If generating random object numbers, create a new UID to * ensure uniqueness; otherwise, use a shared UID because * sequential object numbers already ensure uniqueness. */ if (useRandomIDs()) { space = new UID(); objNum = secureRandom.nextLong(); } else { space = mySpace; objNum = nextObjNum.getAndIncrement(); } } /** * Creates a "well-known" object identifier. * * <p>An <code>ObjID</code> created via this constructor will not * clash with any <code>ObjID</code>s generated via the no-arg * constructor. * * @param objNum object number for well-known object identifier */ public ObjID(int objNum) { space = new UID((short) 0); this.objNum = objNum; } /** * Constructs an object identifier given data read from a stream. */ private ObjID(long objNum, UID space) { this.objNum = objNum; this.space = space; } /** * Marshals a binary representation of this <code>ObjID</code> to * an <code>ObjectOutput</code> instance. * * <p>Specifically, this method first invokes the given stream's * {@link ObjectOutput#writeLong(long)} method with this object * identifier's object number, and then it writes its address * space identifier by invoking its {@link UID#write(DataOutput)} * method with the stream. * * @param out the <code>ObjectOutput</code> instance to write * this <code>ObjID</code> to * * @throws IOException if an I/O error occurs while performing * this operation */ public void write(ObjectOutput out) throws IOException { out.writeLong(objNum); space.write(out); } /** * Constructs and returns a new <code>ObjID</code> instance by * unmarshalling a binary representation from an * <code>ObjectInput</code> instance. * * <p>Specifically, this method first invokes the given stream's * {@link ObjectInput#readLong()} method to read an object number, * then it invokes {@link UID#read(DataInput)} with the * stream to read an address space identifier, and then it * creates and returns a new <code>ObjID</code> instance that * contains the object number and address space identifier that * were read from the stream. * * @param in the <code>ObjectInput</code> instance to read * <code>ObjID</code> from * * @return unmarshalled <code>ObjID</code> instance * * @throws IOException if an I/O error occurs while performing * this operation */ public static ObjID read(ObjectInput in) throws IOException { long num = in.readLong(); UID space = UID.read(in); return new ObjID(num, space); } /** * Returns the hash code value for this object identifier, the * object number. * * @return the hash code value for this object identifier */ public int hashCode() { return (int) objNum; } /** * Compares the specified object with this <code>ObjID</code> for * equality. * * This method returns <code>true</code> if and only if the * specified object is an <code>ObjID</code> instance with the same * object number and address space identifier as this one. * * @param obj the object to compare this <code>ObjID</code> to * * @return <code>true</code> if the given object is equivalent to * this one, and <code>false</code> otherwise */ public boolean equals(Object obj) { if (obj instanceof ObjID) { ObjID id = (ObjID) obj; return objNum == id.objNum && space.equals(id.space); } else { return false; } } /** * Returns a string representation of this object identifier. * * @return a string representation of this object identifier */ /* * The address space identifier is only included in the string * representation if it does not denote the local address space * (or if the randomIDs property was set). */ public String toString() { return "[" + (space.equals(mySpace) ? "" : space + ", ") + objNum + "]"; } private static boolean useRandomIDs() { String value = AccessController.doPrivileged( new GetPropertyAction("java.rmi.server.randomIDs")); return value == null ? true : Boolean.parseBoolean(value); } }