jahiaobject.java

java 写的一个新闻发布系统

// $Id: JahiaObject.java,v 1.2 2002/04/04 08:13:24 pmartin Exp $
//
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//                       __/\ ______|    |__/\.     _______
//            __   .____|    |       \   |    +----+       \
//    _______|  /--|    |    |    -   \  _    |    :    -   \_________
//   \\______: :---|    :    :           |    :    |         \________>
//           |__\---\_____________:______:    :____|____:_____\
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//                 . . . i n   j a h i a   w e   t r u s t . . .
//

package org.jahia.data;

import org.jahia.utils.Semaphore;
import org.jahia.exceptions.JahiaException;

/**
 * The JahiaObject class is the root of all the jahia object. The purpose of
 * this class is to avoid access to any kind of object (pages, containers,
 * fields, users, ....) while they have already been removed from the
 * database.<br/>
 * <br/>
 * Java Virtual Machines do not destroy an object as long as a reference exists
 * on the object. Therefore, for example, when a two users access a page, they
 * get both a reference on the page. Now suppose the first user delete this page,
 * it will be removed from the database permanently. The second user is not
 * aware the page does not exist anymore, and can try to edit this page too.<br/>
 * <br/>
 * On the developper side, the page object still exist, but has no associated
 * entry(ies) in the database anymore. It might leave the database in an
 * unconsistent state if when an object is deleted, all the accesses to the
 * object are denied.<br/>
 * <br/>
 * This class help to avoid this issue. Each object in Jahia should derive
 * from this class and call the {@link #isObjectAlive() isObjectAlive()}
 * method to know if the access can be performed or not. Also when an object
 * is deleted, a call to {@link #killObject() killObject()} should be done
 * in order to block the object for further accesses.
 *
 * @author  Fulco Houkes
 * @version 1.0;
 */
public class JahiaObject
{
    private boolean mObjectIsDEAD;

    //-------------------------------------------------------------------------
    /** Default constructor */
    public JahiaObject ()
    {
        mObjectIsDEAD = false;
    }

    //-------------------------------------------------------------------------
    /** Block the object for all furter accesses. */
    public synchronized void killObject ()
    {
        mObjectIsDEAD = true;
    }

    //-------------------------------------------------------------------------
    /** Test if the object is still alive or has been deleted previously
     *
     * @exception   JahiaException Throws this exception when the object was
     *              previously deleted and is currently unavailable.
     */
    public synchronized void isObjectAlive ()
        throws JahiaException
    {
        if (mObjectIsDEAD) {
            throw new JahiaException ("Access to an unexisting object",
                "An attempt of accessing an in-delete-process-object occured",
                JahiaException.OBJECT_ERROR, JahiaException.ERROR);
        }
    }
}
    // finish class JahiaObject