jdk/src/share/classes/java/lang/reflect/AccessibleObject.java

/*
 * Copyright 1997-2006 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code 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.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code 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 in the LICENSE file that
 * accompanied this code).
 *
 * 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,
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 * have any questions.
 */

package java.lang.reflect;

import java.security.AccessController;
import sun.reflect.ReflectionFactory;
import java.lang.annotation.Annotation;

/**
 * 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 {@code accessible} 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 implements AnnotatedElement {

    /**
     * The Permission object that is used to check whether a client
     * has sufficient privilege to defeat Java language access
     * control checks.
     */
    static final private java.security.Permission ACCESS_PERMISSION =
        new ReflectPermission("suppressAccessChecks");

    /**
     * Convenience method to set the {@code accessible} flag for an
     * array of objects with a single security check (for efficiency).
     *
     * <p>First, if there is a security manager, its
     * {@code checkPermission} method is called with a
     * {@code ReflectPermission("suppressAccessChecks")} permission.
     *
     * <p>A {@code SecurityException} is raised if {@code flag} is
     * {@code true} but accessibility of any of the elements of the input
     * {@code array} 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
     * accessibility of objects is set to {@code flag} for array elements
     * upto (and excluding) the element for which the exception occurred; the
     * accessibility 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 {@code accessible} 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) sm.checkPermission(ACCESS_PERMISSION);
        for (int i = 0; i < array.length; i++) {
            setAccessible0(array[i], flag);
        }
    }

    /**
     * Set the {@code accessible} flag for this object to
     * the indicated boolean value.  A value of {@code true} indicates that
     * the reflected object should suppress Java language access
     * checking when it is used.  A value of {@code false} indicates
     * that the reflected object should enforce Java language access checks.
     *
     * <p>First, if there is a security manager, its
     * {@code checkPermission} method is called with a
     * {@code ReflectPermission("suppressAccessChecks")} permission.
     *
     * <p>A {@code SecurityException} is raised if {@code flag} is
     * {@code true} 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} is raised if this object is a {@link
     * java.lang.reflect.Constructor} object for the class
     * {@code java.lang.Class}, and {@code flag} is true.
     *
     * @param flag the new value for the {@code accessible} 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) 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 {@code accessible} flag for this object.
     *
     * @return the value of the object's {@code accessible} flag
     */
    public boolean isAccessible() {
        return override;
    }

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

    // Indicates whether language-level access checks are overridden
    // by this object. Initializes to "false". This field is used by
    // Field, Method, and Constructor.
    //
    // NOTE: for security purposes, this field must not be visible
    // outside this package.
    boolean override;

    // Reflection factory used by subclasses for creating field,
    // method, and constructor accessors. Note that this is called
    // very early in the bootstrapping process.
    static final ReflectionFactory reflectionFactory = (ReflectionFactory)
        AccessController.doPrivileged
            (new sun.reflect.ReflectionFactory.GetReflectionFactoryAction());

    /**
     * @throws NullPointerException {@inheritDoc}
     * @since 1.5
     */
    public <T extends Annotation> T getAnnotation(Class<T> annotationClass) {
        throw new AssertionError("All subclasses should override this method");
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     * @since 1.5
     */
    public boolean isAnnotationPresent(
        Class<? extends Annotation> annotationClass) {
        return getAnnotation(annotationClass) != null;
    }

    /**
     * @since 1.5
     */
    public Annotation[] getAnnotations() {
        return getDeclaredAnnotations();
    }

    /**
     * @since 1.5
     */
    public Annotation[] getDeclaredAnnotations()  {
        throw new AssertionError("All subclasses should override this method");
    }
}