ELContextCleaner.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.servlet.listener;

import java.lang.reflect.Field;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

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

/**
 * ELContextCleaner
 *
 * Clean up BeanELResolver when the context is going out
 * of service:
 *
 * See http://java.net/jira/browse/GLASSFISH-1649
 * See https://bugs.eclipse.org/bugs/show_bug.cgi?id=353095
 */
public class ELContextCleaner implements ServletContextListener
{
    private static final Logger LOG = Log.getLogger(ELContextCleaner.class);


    public void contextInitialized(ServletContextEvent sce)
    {
    }

    public void contextDestroyed(ServletContextEvent sce)
    {
        try
        {
            //Check that the BeanELResolver class is on the classpath
            Class<?> beanELResolver = Loader.loadClass("javax.el.BeanELResolver");

            //Get a reference via reflection to the properties field which is holding class references
            Field field = getField(beanELResolver);

            //Get rid of references
            purgeEntries(field);

            if (LOG.isDebugEnabled())
                LOG.debug("javax.el.BeanELResolver purged");
        }

        catch (ClassNotFoundException e)
        {
            //BeanELResolver not on classpath, ignore
        }
        catch (SecurityException | IllegalArgumentException | IllegalAccessException e)
        {
            LOG.warn("Cannot purge classes from javax.el.BeanELResolver", e);
        }
        catch (NoSuchFieldException e)
        {
            LOG.debug("Not cleaning cached beans: no such field javax.el.BeanELResolver.properties");
        }

    }


    protected Field getField (Class<?> beanELResolver)
    throws SecurityException, NoSuchFieldException
    {
        if (beanELResolver == null)
            return  null;

        return beanELResolver.getDeclaredField("properties");
    }

    protected void purgeEntries (Field properties)
    throws IllegalArgumentException, IllegalAccessException
    {
        if (properties == null)
            return;

        if (!properties.isAccessible())
            properties.setAccessible(true);

        Map map = (Map) properties.get(null);
        if (map == null)
            return;

        Iterator<Class<?>> itor = map.keySet().iterator();
        while (itor.hasNext())
        {
            Class<?> clazz = itor.next();
            if (LOG.isDebugEnabled())
                LOG.debug("Clazz: "+clazz+" loaded by "+clazz.getClassLoader());
            if (Thread.currentThread().getContextClassLoader().equals(clazz.getClassLoader()))
            {
                itor.remove();
                if (LOG.isDebugEnabled())
                    LOG.debug("removed");
            }
            else
            {
                if (LOG.isDebugEnabled())
                    LOG.debug("not removed: "+"contextclassloader="+Thread.currentThread().getContextClassLoader()+"clazz's classloader="+clazz.getClassLoader());
            }
        }
    }
}