GuardedObject.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * accompanied this code).
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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}
 * method, which invokes the
 * {@code checkGuard} method on the Guard object that is
 * guarding access. If access is not allowed,
 * an exception is thrown.
 *
 * @see Guard
 * @see Permission
 *
 * @author Roland Schemers
 * @author Li Gong
 */

public class GuardedObject implements java.io.Serializable {

    private static final long serialVersionUID = -5240450096227834308L;

    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 void writeObject(java.io.ObjectOutputStream oos)
        throws java.io.IOException
    {
        if (guard != null)
            guard.checkGuard(object);

        oos.defaultWriteObject();
    }
}