ManagedAttributeListener.java

//
//  ========================================================================
//  Copyright (c) 1995-2017 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.server.handler;

import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;

/* ------------------------------------------------------------ */
/** Enable Jetty style JMX MBeans from within a Context 
 */
public class ManagedAttributeListener implements  ServletContextListener, ServletContextAttributeListener
{
    private static final Logger LOG = Log.getLogger(ManagedAttributeListener.class);

    final Set<String> _managedAttributes=new HashSet<>();
    final ContextHandler _context;
    
    public ManagedAttributeListener(ContextHandler context,String... managedAttributes)
    {
        _context=context;

        for (String attr:managedAttributes)
            _managedAttributes.add(attr);
        
        if (LOG.isDebugEnabled())
            LOG.debug("managedAttributes {}",_managedAttributes);
    }

    @Override
    public void attributeReplaced(ServletContextAttributeEvent event)
    {
        if (_managedAttributes.contains(event.getName()))
            updateBean(event.getName(),event.getValue(),event.getServletContext().getAttribute(event.getName()));
    }
    
    @Override
    public void attributeRemoved(ServletContextAttributeEvent event)
    {
        if (_managedAttributes.contains(event.getName()))
            updateBean(event.getName(),event.getValue(),null);                    
    }
    
    @Override
    public void attributeAdded(ServletContextAttributeEvent event)
    {
        if (_managedAttributes.contains(event.getName()))
            updateBean(event.getName(),null,event.getValue());    
    }

    @Override
    public void contextInitialized(ServletContextEvent event)
    {                 
        // Update existing attributes
        Enumeration<String> e = event.getServletContext().getAttributeNames();
        while (e.hasMoreElements())
        {
            String name = e.nextElement();
            if (_managedAttributes.contains(name))
                updateBean(name,null,event.getServletContext().getAttribute(name));
        }
    }
    
    @Override
    public void contextDestroyed(ServletContextEvent event)
    {
        Enumeration<String> e = _context.getServletContext().getAttributeNames();
        while (e.hasMoreElements())
        {
            String name = e.nextElement();
            if (_managedAttributes.contains(name))
                updateBean(name,event.getServletContext().getAttribute(name),null);
        }
    }
    
    protected void updateBean(String name,Object oldBean,Object newBean)
    {
        LOG.info("update {} {}->{} on {}",name,oldBean,newBean,_context);
        if (LOG.isDebugEnabled())
            LOG.debug("update {} {}->{} on {}",name,oldBean,newBean,_context);
        _context.updateBean(oldBean,newBean,false);
    }
}