//
   //  ========================================================================
   //  Copyright (c) 1995-2015 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.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(this.getClass(), "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);
 
         ConcurrentHashMap<Class<?>, Object> map = (ConcurrentHashMap<Class<?>, Object>) 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());
             }
         }
     }
 }