guardedobject.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 104 行

/*
 * @(#)GuardedObject.java	1.17 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package java.security;

/**
 * A GuardedObject is an object that is used to protect access to
 * another object.
 *
 * <p>A GuardedObject encapsulates a target object and a Guard object,
 * such that access to the target object is possible
 * only if the Guard object allows it.
 * Once an object is encapsulated by a GuardedObject,
 * access to that object is controlled by the <code>getObject</code>
 * method, which invokes the
 * <code>checkGuard</code> method on the Guard object that is
 * guarding access. If access is not allowed,
 * an exception is thrown.
 *
 * @see Guard
 * @see Permission
 *
 * @version 1.11 00/02/02
 * @author Roland Schemers
 * @author Li Gong
 */

public class GuardedObject implements java.io.Serializable {

    private Object object; // the object we are guarding
    private Guard guard;   // the guard

    /**
     * Constructs a GuardedObject using the specified object and guard.
     * If the Guard object is null, then no restrictions will
     * be placed on who can access the object.
     *
     * @param object the object to be guarded.
     *
     * @param guard the Guard object that guards access to the object.
     */

    public GuardedObject(Object object, Guard guard)
    {
        this.guard = guard;
        this.object = object;
    }

    /**
     * Retrieves the guarded object, or throws an exception if access
     * to the guarded object is denied by the guard.
     *
     * @return the guarded object.
     *
     * @exception SecurityException if access to the guarded object is
     * denied.
     */
    public Object getObject()
        throws SecurityException
    {
        if (guard != null)
            guard.checkGuard(object);

        return object;
    }

    /**
     * Writes this object out to a stream (i.e., serializes it).
     * We check the guard if there is one.
     */
    private synchronized void writeObject(java.io.ObjectOutputStream oos)
        throws java.io.IOException
    {
        if (guard != null)
            guard.checkGuard(object);
	
	oos.defaultWriteObject();
    }
}