accessibleobject.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 173 行

/*
 * @(#)AccessibleObject.java	1.22 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.lang.reflect;

/**
 * The AccessibleObject class is the base class for Field, Method and
 * Constructor objects.  It provides the ability to flag a reflected
 * object as suppressing default Java language access control checks
 * when it is used.  The access checks--for public, default (package)
 * access, protected, and private members--are performed when Fields,
 * Methods or Constructors are used to set or get fields, to invoke
 * methods, or to create and initialize new instances of classes,
 * respectively.
 *
 * <p>Setting the <tt>accessible</tt> flag in a reflected object
 * permits sophisticated applications with sufficient privilege, such
 * as Java Object Serialization or other persistence mechanisms, to
 * manipulate objects in a manner that would normally be prohibited.
 *
 * @see Field
 * @see Method
 * @see Constructor
 * @see ReflectPermission
 *
 * @since 1.2
 */
public
class AccessibleObject {

    /**
     * The Permission object that is used to check whether a client
     * has sufficient privilege to defeat Java language access
     * control checks.
     */
    static private java.security.Permission ACCESS_PERMISSION;

    static private void initAccessPermission() {
	ACCESS_PERMISSION = new ReflectPermission("suppressAccessChecks");
    }

    /**
     * Convenience method to set the <tt>accessible</tt> flag for an
     * array of objects with a single security check (for efficiency).
     *
     * <p>First, if there is a security manager, its
     * <code>checkPermission</code> method is called with a
     * <code>ReflectPermission("suppressAccessChecks")</code> permission.
     *
     * <p>A <code>SecurityException</code> is raised if <code>flag</code> is
     * <code>true</code> but accessibility of any of the elements of the input
     * <code>array</code> may not be changed (for example, if the element
     * object is a {@link Constructor} object for the class {@link
     * java.lang.Class}).  In the event of such a SecurityException, the
     * accessiblity of objects is set to <code>flag</code> for array elements
     * upto (and excluding) the element for which the exception occurred; the
     * accessiblity of elements beyond (and including) the element for which
     * the exception occurred is unchanged.
     *
     * @param array the array of AccessibleObjects
     * @param flag  the new value for the <tt>accessible</tt> flag
     *              in each object
     * @throws SecurityException if the request is denied.
     * @see SecurityManager#checkPermission
     * @see java.lang.RuntimePermission
     */
    public static void setAccessible(AccessibleObject[] array, boolean flag)
	throws SecurityException {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	    if (ACCESS_PERMISSION == null) {
		initAccessPermission();
	    }
	    sm.checkPermission(ACCESS_PERMISSION);
	}
	for (int i = 0; i < array.length; i++) {
	    setAccessible0(array[i], flag);
	}
    }

    /**
     * Set the <tt>accessible</tt> flag for this object to
     * the indicated boolean value.  A value of <tt>true</tt> indicates that
     * the reflected object should suppress Java language access
     * checking when it is used.  A value of <tt>false</tt> indicates 
     * that the reflected object should enforce Java language access checks.
     *
     * <p>First, if there is a security manager, its
     * <code>checkPermission</code> method is called with a
     * <code>ReflectPermission("suppressAccessChecks")</code> permission.
     * 
     * <p>A <code>SecurityException</code> is raised if <code>flag</code> is
     * <code>true</code> but accessibility of this object may not be changed
     * (for example, if this element object is a {@link Constructor} object for
     * the class {@link java.lang.Class}).
     *
     * <p>A <code>SecurityException</code> is raised if this object is a {@link
     * java.lang.reflect.Constructor} object for the class
     * <code>java.lang.Class</code>, and <code>flag</code> is true.
     *
     * @param flag the new value for the <tt>accessible</tt> flag
     * @throws SecurityException if the request is denied.
     * @see SecurityManager#checkPermission
     * @see java.lang.RuntimePermission
     */
    public void setAccessible(boolean flag) throws SecurityException {
	SecurityManager sm = System.getSecurityManager();
	if (sm != null) {
	    if (ACCESS_PERMISSION == null) {
		initAccessPermission();
	    }
	    sm.checkPermission(ACCESS_PERMISSION);
	}
	setAccessible0(this, flag);
    }

    /* Check that you aren't exposing java.lang.Class.<init>. */
    private static void setAccessible0(AccessibleObject obj, boolean flag)
	throws SecurityException
    {
	if (obj instanceof Constructor && flag == true) {
	    Constructor c = (Constructor)obj;
	    if (c.getDeclaringClass() == Class.class) {
		throw new SecurityException("Can not make a java.lang.Class" +
					    " constructor accessible");
	    }
	}
	obj.override = flag;
    }

    /**
     * Get the value of the <tt>accessible</tt> flag for this object.
     *
     * @return the value of the object's <tt>accessible</tt> flag
     */
    public boolean isAccessible() {
	return override;
    }

    /**
     * Constructor: only used by the Java Virtual Machine.
     */
    protected AccessibleObject() {}

    // N.B. jvm depends on this field name, and initializes to <tt>false</tt>.
    private boolean override;

}