// ========================================================================
   // Copyright (c) 2008-2009 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.session;
  
  import java.io.ByteArrayInputStream;
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.sql.Connection;
  import java.sql.PreparedStatement;
  import java.sql.ResultSet;
  import java.sql.SQLException;
  import java.util.HashMap;
  import java.util.List;
  import java.util.ListIterator;
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.atomic.AtomicReference;
  
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpSessionEvent;
  import javax.servlet.http.HttpSessionListener;
  
  import org.eclipse.jetty.server.SessionIdManager;
  import org.eclipse.jetty.server.handler.ContextHandler;
  import org.eclipse.jetty.util.log.Log;
  
  /**
   * JDBCSessionManager
   *
   * SessionManager that persists sessions to a database to enable clustering.
   * 
   * Session data is persisted to the JettySessions table:
   * 
   * rowId (unique in cluster: webapp name/path + virtualhost + sessionId)
   * contextPath (of the context owning the session)
   * sessionId (unique in a context)
   * lastNode (name of node last handled session)
   * accessTime (time in milliseconds session was accessed)
   * lastAccessTime (previous time in milliseconds session was accessed)
   * createTime (time in milliseconds session created)
   * cookieTime (time in milliseconds session cookie created)
   * lastSavedTime (last time in milliseconds session access times were saved)
   * expiryTime (time in milliseconds that the session is due to expire)
   * map (attribute map)
   * 
   * As an optimization, to prevent thrashing the database, we do not persist
   * the accessTime and lastAccessTime every time the session is accessed. Rather,
   * we write it out every so often. The frequency is controlled by the saveIntervalSec
   * field.
   */
  public class JDBCSessionManager extends AbstractSessionManager
  {  
      protected  String __insertSession;  
      protected  String __deleteSession; 
      protected  String __selectSession;   
      protected  String __updateSession;  
      protected  String __updateSessionNode; 
      protected  String __updateSessionAccessTime;
      protected  String __sessionTableRowId;
      
      private ConcurrentHashMap<String, AbstractSession> _sessions;
      protected long _saveIntervalSec = 60; //only persist changes to session access times every 60 secs
    
      /**
       * SessionData
       *
       * Persistable data about a session.
       */
      public class SessionData
      {
          private final String _id;
          private String _rowId;
          private long _accessed;
          private long _lastAccessed;
          private long _maxIdleMs=-1;
          private long _cookieSet;
          private long _created;
          private Map<String,Object> _attributes;
          private String _lastNode;
          private String _canonicalContext;
          private long _lastSaved;
          private long _expiryTime;
          private String _virtualHost;
  
         public SessionData (String sessionId)
         {
             _id=sessionId;
             _created=System.currentTimeMillis();
             _accessed = _created;
             _attributes = new HashMap<String,Object>();
             _lastNode = getSessionIdManager().getWorkerName();
         }
         
         public SessionData (String sessionId,Map<String,Object> attributes)
         {
             _id=sessionId;
             _created=System.currentTimeMillis();
             _accessed = _created;
             _attributes = attributes;
             _lastNode = getSessionIdManager().getWorkerName();
         }
 
         public synchronized String getId ()
         {
             return _id;
         }
 
         public synchronized long getCreated ()
         {
             return _created;
         }
         
         protected synchronized void setCreated (long ms)
         {
             _created = ms;
         }
         
         public synchronized long getAccessed ()
         {
             return _accessed;
         }
         
         protected synchronized void setAccessed (long ms)
         {
             _accessed = ms;
         }
         
         
         public synchronized void setMaxIdleMs (long ms)
         {
             _maxIdleMs = ms;
         }
 
         public synchronized long getMaxIdleMs()
         {
             return _maxIdleMs;
         }
 
         public synchronized void setLastAccessed (long ms)
         {
             _lastAccessed = ms;
         }
 
         public synchronized long getLastAccessed()
         {
             return _lastAccessed;
         }
 
         public void setCookieSet (long ms)
         {
             _cookieSet = ms;
         }
 
         public synchronized long getCookieSet ()
         {
             return _cookieSet;
         }
         
         public synchronized void setRowId (String rowId)
         {
             _rowId=rowId;
         }
         
         protected synchronized String getRowId()
         {
             return _rowId;
         }
         
         protected synchronized Map<String,Object> getAttributeMap ()
         {
             return _attributes;
         }
         
         protected synchronized void setAttributeMap (Map<String,Object> map)
         {
             _attributes = map;
         } 
         
         public synchronized void setLastNode (String node)
         {
             _lastNode=node;
         }
         
         public synchronized String getLastNode ()
         {
             return _lastNode;
         }
         
         public synchronized void setCanonicalContext(String str)
         {
             _canonicalContext=str;
         }
         
         public synchronized String getCanonicalContext ()
         {
             return _canonicalContext;
         }
         
         public synchronized long getLastSaved ()
         {
             return _lastSaved;
         }
         
         public synchronized void setLastSaved (long time)
         {
             _lastSaved=time;
         }
         
         public synchronized void setExpiryTime (long time)
         {
             _expiryTime=time;      
         }
         
         public synchronized long getExpiryTime ()
         {
             return _expiryTime;
         }
         
         public synchronized void setVirtualHost (String vhost)
         {
             _virtualHost=vhost;
         }
         
         public synchronized String getVirtualHost ()
         {
             return _virtualHost;
         }
         
         @Override
         public String toString ()
         {
             return "Session rowId="+_rowId+",id="+_id+",lastNode="+_lastNode+
                             ",created="+_created+",accessed="+_accessed+
                             ",lastAccessed="+_lastAccessed+",cookieSet="+_cookieSet+
                             "lastSaved="+_lastSaved;
         }
     }
 
     
     
     /**
      * Session
      *
      * Session instance in memory of this node.
      */
     public class Session extends AbstractSession
     {
         private static final long serialVersionUID = 5208464051134226143L;
         private final SessionData _data;
         private boolean _dirty=false;
 
         /**
          * Session from a request.
          * 
          * @param request
          */
         protected Session (HttpServletRequest request)
         {
             super(JDBCSessionManager.this,request);   
             _data = new SessionData(getClusterId(),_jdbcAttributes);
             if (_dftMaxIdleSecs>0)
                 _data.setMaxIdleMs(_dftMaxIdleSecs*1000);
             _data.setCanonicalContext(canonicalize(_context.getContextPath()));
             _data.setVirtualHost(getVirtualHost(_context));
             int maxInterval=getMaxInactiveInterval();
             _data.setExpiryTime(maxInterval <= 0 ? 0 : (System.currentTimeMillis() + maxInterval*1000));
         }
 
         /**
           * Session restored in database.
           * @param data
           */
          protected Session (long accessed, SessionData data)
          {
              super(JDBCSessionManager.this,data.getCreated(), accessed, data.getId());
              _data=data;
              if (_dftMaxIdleSecs>0)
                  _data.setMaxIdleMs(_dftMaxIdleSecs*1000);
              _jdbcAttributes.putAll(_data.getAttributeMap());
              _data.setAttributeMap(_jdbcAttributes);
          }
          
          @Override
         public void setAttribute (String name, Object value)
          {
              super.setAttribute(name, value);
              _dirty=true;
          }
 
          @Override
         public void removeAttribute (String name)
          {
              super.removeAttribute(name); 
              _dirty=true;
          }
          
          @Override
         protected void cookieSet()
          {
              _data.setCookieSet(_data.getAccessed());
          }
 
         /** 
          * Entry to session.
          * Called by SessionHandler on inbound request and the session already exists in this node's memory.
          * 
          * @see org.eclipse.jetty.server.session.AbstractSession#access(long)
          */
         @Override
         protected boolean access(long time)
         {
             if (super.access(time))
             {
                 _data.setLastAccessed(_data.getAccessed());
                 _data.setAccessed(time);
 
                 int maxInterval=getMaxInactiveInterval();
                 _data.setExpiryTime(maxInterval <= 0 ? 0 : (time + maxInterval*1000));
                 return true;
             }
             return false;
         }
 
         /** 
          * Exit from session
          * @see org.eclipse.jetty.server.session.AbstractSession#complete()
          */
         @Override
         protected void complete()
         {
             super.complete();
             try
             {
                 if (_dirty)
                 { 
                     //The session attributes have changed, write to the db, ensuring
                     //http passivation/activation listeners called
                     willPassivate();
                     updateSession(_data);
                     didActivate();
                 }
                 else if ((_data._accessed - _data._lastSaved) >= (getSaveInterval() * 1000))
                 {  
                     updateSessionAccessTime(_data);
                 }
             }
             catch (Exception e)
             {
                 Log.warn("Problem persisting changed session data id="+getId(), e);
             }
             finally
             {
                 _dirty=false;
             }
         }
         
         @Override
         protected void timeout() throws IllegalStateException
         {
             if (Log.isDebugEnabled()) Log.debug("Timing out session id="+getClusterId());
             super.timeout();
         }
     }
     
     
     
     
     /**
      * ClassLoadingObjectInputStream
      *
      *
      */
     protected class ClassLoadingObjectInputStream extends ObjectInputStream
     {
         public ClassLoadingObjectInputStream(java.io.InputStream in) throws IOException
         {
             super(in);
         }
 
         public ClassLoadingObjectInputStream () throws IOException
         {
             super();
         }
 
         @Override
         public Class<?> resolveClass (java.io.ObjectStreamClass cl) throws IOException, ClassNotFoundException
         {
             try
             {
                 return Class.forName(cl.getName(), false, Thread.currentThread().getContextClassLoader());
             }
             catch (ClassNotFoundException e)
             {
                 return super.resolveClass(cl);
             }
         }
     }
     
     
 
 
     /**
      * Set the time in seconds which is the interval between
      * saving the session access time to the database.
      * 
      * This is an optimization that prevents the database from
      * being overloaded when a session is accessed very frequently.
      * 
      * On session exit, if the session attributes have NOT changed,
      * the time at which we last saved the accessed
      * time is compared to the current accessed time. If the interval
      * is at least saveIntervalSecs, then the access time will be
      * persisted to the database.
      * 
      * If any session attribute does change, then the attributes and
      * the accessed time are persisted.
      * 
      * @param sec
      */
     public void setSaveInterval (long sec)
     {
         _saveIntervalSec=sec;
     }
   
     public long getSaveInterval ()
     {
         return _saveIntervalSec;
     }
 
    
     
     /**
      * A method that can be implemented in subclasses to support
      * distributed caching of sessions. This method will be
      * called whenever the session is written to the database
      * because the session data has changed.
      * 
      * This could be used eg with a JMS backplane to notify nodes
      * that the session has changed and to delete the session from
      * the node's cache, and re-read it from the database.
      * @param session
      */
     public void cacheInvalidate (Session session)
     {
         
     }
     
     
     /** 
      * A session has been requested by it's id on this node.
      * 
      * Load the session by id AND context path from the database.
      * Multiple contexts may share the same session id (due to dispatching)
      * but they CANNOT share the same contents.
      * 
      * Check if last node id is my node id, if so, then the session we have
      * in memory cannot be stale. If another node used the session last, then
      * we need to refresh from the db.
      * 
      * NOTE: this method will go to the database, so if you only want to check 
      * for the existence of a Session in memory, use _sessions.get(id) instead.
      * 
      * @see org.eclipse.jetty.server.session.AbstractSessionManager#getSession(java.lang.String)
      */
     @Override
     public Session getSession(String idInCluster)
     {
         Session session = (Session)_sessions.get(idInCluster);
         
         synchronized (this)
         {        
             try
             {                
                 //check if we need to reload the session - 
                 //as an optimization, don't reload on every access
                 //to reduce the load on the database. This introduces a window of 
                 //possibility that the node may decide that the session is local to it,
                 //when the session has actually been live on another node, and then
                 //re-migrated to this node. This should be an extremely rare occurrence,
                 //as load-balancers are generally well-behaved and consistently send 
                 //sessions to the same node, changing only iff that node fails. 
                 SessionData data = null;
                 long now = System.currentTimeMillis();
                 if (Log.isDebugEnabled()) 
                 {
                     if (session==null)
                         Log.debug("getSession("+idInCluster+"): not in session map,"+
                                 " now="+now+
                                 " lastSaved="+(session==null?0:session._data._lastSaved)+
                                 " interval="+(_saveIntervalSec * 1000));
                     else
                         Log.debug("getSession("+idInCluster+"): in session map, "+
                                 " now="+now+
                                 " lastSaved="+(session==null?0:session._data._lastSaved)+
                                 " interval="+(_saveIntervalSec * 1000)+
                                 " lastNode="+session._data.getLastNode()+
                                 " thisNode="+getSessionIdManager().getWorkerName()+
                                 " difference="+(now - session._data._lastSaved));
                 }
                 
                 if (session==null || ((now - session._data._lastSaved) >= (_saveIntervalSec * 1000)))
                 {       
                     Log.debug("getSession("+idInCluster+"): no session in session map or stale session. Reloading session data from db.");
                     data = loadSession(idInCluster, canonicalize(_context.getContextPath()), getVirtualHost(_context));
                 }
                 else if ((now - session._data._lastSaved) >= (_saveIntervalSec * 1000))
                 {
                     Log.debug("getSession("+idInCluster+"): stale session. Reloading session data from db.");
                     data = loadSession(idInCluster, canonicalize(_context.getContextPath()), getVirtualHost(_context));
                 }
                 else
                 {
                     Log.debug("getSession("+idInCluster+"): session in session map"); 
                     data = session._data;
                 }
                 
                 if (data != null)
                 {
                     if (!data.getLastNode().equals(getSessionIdManager().getWorkerName()) || session==null)
                     {
                         //if the session has no expiry, or it is not already expired
                         if (data._expiryTime <= 0 || data._expiryTime > now)
                         {
                             Log.debug("getSession("+idInCluster+"): lastNode="+data.getLastNode()+" thisNode="+getSessionIdManager().getWorkerName());
                             data.setLastNode(getSessionIdManager().getWorkerName());
                             //session last used on a different node, or we don't have it in memory
                             session = new Session(now,data);
                             _sessions.put(idInCluster, session);
                             session.didActivate();
                             //TODO is this the best way to do this? Or do this on the way out using
                             //the _dirty flag?
                             updateSessionNode(data);
                         }
                         else
                             if (Log.isDebugEnabled()) Log.debug("getSession("+idInCluster+"): Session has expired");
                         
                     }
                     else
                         if (Log.isDebugEnabled()) Log.debug("getSession("+idInCluster+"): Session not stale "+session._data);
                     //session in db shares same id, but is not for this context
                 }
                 else
                 {
                     //No session in db with matching id and context path.
                     session=null;
                     if (Log.isDebugEnabled()) Log.debug("getSession("+idInCluster+"): No session in database matching id="+idInCluster);
                 }
                 
                 return session;
             }
             catch (Exception e)
             {
                 Log.warn("Unable to load session from database", e);
                 return null;
             }
         }
     }
     
     /** 
      * Get the number of sessions.
      * 
      * @see org.eclipse.jetty.server.session.AbstractSessionManager#getSessions()
      */
     @Override
     public int getSessions()
     {
         int size = 0;
         synchronized (this)
         {
             size = _sessions.size();
         }
         return size;
     }
 
 
     /** 
      * Start the session manager.
      * 
      * @see org.eclipse.jetty.server.session.AbstractSessionManager#doStart()
      */
     @Override
     public void doStart() throws Exception
     {
         if (_sessionIdManager==null)
             throw new IllegalStateException("No session id manager defined");
         
         prepareTables();
      
         _sessions = new ConcurrentHashMap<String, AbstractSession>();
         super.doStart();
     }
     
     
     /** 
      * Stop the session manager.
      * 
      * @see org.eclipse.jetty.server.session.AbstractSessionManager#doStop()
      */
     @Override
     public void doStop() throws Exception
     {
         _sessions.clear();
         _sessions = null;
         
         super.doStop();
     } 
     
     @Override
     protected void invalidateSessions()
     {
         //Do nothing - we don't want to remove and
         //invalidate all the sessions because this
         //method is called from doStop(), and just
         //because this context is stopping does not
         //mean that we should remove the session from
         //any other nodes
     }
 
     
     /**
      * Invalidate a session.
      * 
      * @param idInCluster
      */
     protected void invalidateSession (String idInCluster)
     {
         Session session = null;
         synchronized (this)
         {
             session = (Session)_sessions.get(idInCluster);
         }
         
         if (session != null)
         {
             session.invalidate();
         }
     }
    
     /** 
      * Delete an existing session, both from the in-memory map and
      * the database.
      * 
      * @see org.eclipse.jetty.server.session.AbstractSessionManager#removeSession(java.lang.String)
      */
     @Override
     protected boolean removeSession(String idInCluster)
     {
         synchronized (this)
         {       
             Session session = (Session)_sessions.remove(idInCluster);
             try
             {
                 if (session != null)
                     deleteSession(session._data);
             }
             catch (Exception e)
             {
                 Log.warn("Problem deleting session id="+idInCluster, e);
             }
             return session!=null;
         }
     }
 
 
     /** 
      * Add a newly created session to our in-memory list for this node and persist it.
      * 
      * @see org.eclipse.jetty.server.session.AbstractSessionManager#addSession(org.eclipse.jetty.server.session.AbstractSession)
      */
     @Override
     protected void addSession(AbstractSession session)
     {
         if (session==null)
             return;
 
         synchronized (this)
         {
             _sessions.put(session.getClusterId(), session);
         }
         
         //TODO or delay the store until exit out of session? If we crash before we store it
         //then session data will be lost.
         try
         {
             session.willPassivate();
             storeSession(((JDBCSessionManager.Session)session)._data);
             session.didActivate();
         }
         catch (Exception e)
         {
             Log.warn("Unable to store new session id="+session.getId() , e);
         }
     }
 
 
     /** 
      * Make a new Session.
      * 
      * @see org.eclipse.jetty.server.session.AbstractSessionManager#newSession(javax.servlet.http.HttpServletRequest)
      */
     @Override
     protected AbstractSession newSession(HttpServletRequest request)
     {
         return new Session(request);
     }
     
     /* ------------------------------------------------------------ */
     /** Remove session from manager 
      * @param session The session to remove
      * @param invalidate True if {@link HttpSessionListener#sessionDestroyed(HttpSessionEvent)} and
      * {@link SessionIdManager#invalidateAll(String)} should be called.
      */
     @Override
     public void removeSession(AbstractSession session, boolean invalidate)
     {
         // Remove session from context and global maps
         boolean removed = false;
         
         synchronized (this)
         {
             //take this session out of the map of sessions for this context
             if (getSession(session.getClusterId()) != null)
             {
                 removed = true;
                 removeSession(session.getClusterId());
             }
         }
 
         if (removed)
         {
             // Remove session from all context and global id maps
             _sessionIdManager.removeSession(session);
             
             if (invalidate)
                 _sessionIdManager.invalidateAll(session.getClusterId());
             
             if (invalidate && !_sessionListeners.isEmpty())
             {
                 HttpSessionEvent event=new HttpSessionEvent(session);
                 for (HttpSessionListener l : _sessionListeners)
                     l.sessionDestroyed(event);
             }
             if (!invalidate)
             {
                 session.willPassivate();
             }
         }
     }
     
     
     /**
      * Expire any Sessions we have in memory matching the list of
      * expired Session ids.
      * 
      * @param sessionIds
      */
     protected void expire (List<?> sessionIds)
     { 
         //don't attempt to scavenge if we are shutting down
         if (isStopping() || isStopped())
             return;
 
         //Remove any sessions we already have in memory that match the ids
         Thread thread=Thread.currentThread();
         ClassLoader old_loader=thread.getContextClassLoader();
         ListIterator<?> itor = sessionIds.listIterator();
 
         try
         {
             while (itor.hasNext())
             {
                 String sessionId = (String)itor.next();
                 if (Log.isDebugEnabled()) Log.debug("Expiring session id "+sessionId);
                 
                 Session session = (Session)_sessions.get(sessionId);
                 if (session != null)
                 {
                     session.timeout();
                     itor.remove();
                 }
                 else
                 {
                     if (Log.isDebugEnabled()) Log.debug("Unrecognized session id="+sessionId);
                 }
             }
         }
         catch (Throwable t)
         {
             if (t instanceof ThreadDeath)
                 throw ((ThreadDeath)t);
             else
                 Log.warn("Problem expiring sessions", t);
         }
         finally
         {
             thread.setContextClassLoader(old_loader);
         }
     }
     
  
     protected void prepareTables ()
     {
         __sessionTableRowId = ((JDBCSessionIdManager)_sessionIdManager)._sessionTableRowId;
         
         __insertSession = "insert into "+((JDBCSessionIdManager)_sessionIdManager)._sessionTable+
                           " ("+__sessionTableRowId+", sessionId, contextPath, virtualHost, lastNode, accessTime, lastAccessTime, createTime, cookieTime, lastSavedTime, expiryTime, map) "+
                           " values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)";
 
         __deleteSession = "delete from "+((JDBCSessionIdManager)_sessionIdManager)._sessionTable+
                           " where "+__sessionTableRowId+" = ?";
 
         __selectSession = "select * from "+((JDBCSessionIdManager)_sessionIdManager)._sessionTable+
                           " where sessionId = ? and contextPath = ? and virtualHost = ?";
 
         __updateSession = "update "+((JDBCSessionIdManager)_sessionIdManager)._sessionTable+
                           " set lastNode = ?, accessTime = ?, lastAccessTime = ?, lastSavedTime = ?, expiryTime = ?, map = ? where "+__sessionTableRowId+" = ?";
 
         __updateSessionNode = "update "+((JDBCSessionIdManager)_sessionIdManager)._sessionTable+
                               " set lastNode = ? where "+__sessionTableRowId+" = ?";
 
         __updateSessionAccessTime = "update "+((JDBCSessionIdManager)_sessionIdManager)._sessionTable+
                                     " set lastNode = ?, accessTime = ?, lastAccessTime = ?, lastSavedTime = ?, expiryTime = ? where "+__sessionTableRowId+" = ?";
     }
     
     /**
      * Load a session from the database
      * @param id
      * @return the session data that was loaded
      * @throws Exception
      */
     protected SessionData loadSession (final String id, final String canonicalContextPath, final String vhost)
     throws Exception
     {
         final AtomicReference<SessionData> _reference = new AtomicReference<SessionData>();
         final AtomicReference<Exception> _exception = new AtomicReference<Exception>();
         Runnable load = new Runnable()
         {
             @SuppressWarnings("unchecked")
             public void run()
             {
                 SessionData data = null;
                 Connection connection=null;
                 PreparedStatement statement = null;
                 try
                 {   
                     connection = getConnection();
                     statement = connection.prepareStatement(__selectSession);
                     statement.setString(1, id);
                     statement.setString(2, canonicalContextPath);
                     statement.setString(3, vhost);
                     ResultSet result = statement.executeQuery();
                     if (result.next())
                     {
                         data = new SessionData(id);
                         data.setRowId(result.getString(__sessionTableRowId));
                         data.setCookieSet(result.getLong("cookieTime"));
                         data.setLastAccessed(result.getLong("lastAccessTime"));
                         data.setAccessed (result.getLong("accessTime"));
                         data.setCreated(result.getLong("createTime"));
                         data.setLastNode(result.getString("lastNode"));
                         data.setLastSaved(result.getLong("lastSavedTime"));
                         data.setExpiryTime(result.getLong("expiryTime"));
                         data.setCanonicalContext(result.getString("contextPath"));
                         data.setVirtualHost(result.getString("virtualHost"));
 
                         InputStream is = ((JDBCSessionIdManager)getSessionIdManager())._dbAdaptor.getBlobInputStream(result, "map");
                         ClassLoadingObjectInputStream ois = new ClassLoadingObjectInputStream (is);
                         Object o = ois.readObject();
                         data.setAttributeMap((Map<String,Object>)o);
                         ois.close();
 
                         if (Log.isDebugEnabled())
                             Log.debug("LOADED session "+data);
                     }
                     _reference.set(data);
                 }
                 catch (Exception e)
                 {
                     _exception.set(e);
                 }
                 finally
                 {
                     if (connection!=null)
                     {
                         try { connection.close();}
                         catch(Exception e) { Log.warn(e); }
                     }
                 }  
             }
         };
         
         if (_context==null)
             load.run();
         else
             _context.getContextHandler().handle(load);
         
         if (_exception.get()!=null)
             throw _exception.get();
         
         return _reference.get();
     }
     
     /**
      * Insert a session into the database.
      * 
      * @param data
      * @throws Exception
      */
     protected void storeSession (SessionData data)
     throws Exception
     {
         if (data==null)
             return;
         
         //put into the database      
         Connection connection = getConnection();
         PreparedStatement statement = null;
         try
         {   
             String rowId = calculateRowId(data);
             
             long now = System.currentTimeMillis();
             connection.setAutoCommit(true);
             statement = connection.prepareStatement(__insertSession);
             statement.setString(1, rowId); //rowId
             statement.setString(2, data.getId()); //session id
             statement.setString(3, data.getCanonicalContext()); //context path
             statement.setString(4, data.getVirtualHost()); //first vhost
             statement.setString(5, getSessionIdManager().getWorkerName());//my node id
             statement.setLong(6, data.getAccessed());//accessTime
             statement.setLong(7, data.getLastAccessed()); //lastAccessTime
             statement.setLong(8, data.getCreated()); //time created
             statement.setLong(9, data.getCookieSet());//time cookie was set
             statement.setLong(10, now); //last saved time
             statement.setLong(11, data.getExpiryTime());
             
             ByteArrayOutputStream baos = new ByteArrayOutputStream();
             ObjectOutputStream oos = new ObjectOutputStream(baos);
             oos.writeObject(data.getAttributeMap());
             byte[] bytes = baos.toByteArray();
             
             ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
             statement.setBinaryStream(12, bais, bytes.length);//attribute map as blob
             
             statement.executeUpdate();
             data.setRowId(rowId); //set it on the in-memory data as well as in db
             data.setLastSaved(now);
 
             
             if (Log.isDebugEnabled())
                 Log.debug("Stored session "+data);
         }   
         finally
         {
             if (connection!=null)
                 connection.close();
         }
     }
     
     
     /**
      * Update data on an existing persisted session.
      * 
      * @param data
      * @throws Exception
      */
     protected void updateSession (SessionData data)
     throws Exception
     {
         if (data==null)
             return;
         
         Connection connection = getConnection();
         PreparedStatement statement = null;
         try
         {              
             long now = System.currentTimeMillis();
             connection.setAutoCommit(true);
             statement = connection.prepareStatement(__updateSession);     
             statement.setString(1, getSessionIdManager().getWorkerName());//my node id
             statement.setLong(2, data.getAccessed());//accessTime
             statement.setLong(3, data.getLastAccessed()); //lastAccessTime
             statement.setLong(4, now); //last saved time
             statement.setLong(5, data.getExpiryTime());
             
             ByteArrayOutputStream baos = new ByteArrayOutputStream();
             ObjectOutputStream oos = new ObjectOutputStream(baos);
             oos.writeObject(data.getAttributeMap());
             byte[] bytes = baos.toByteArray();
             ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
             
             statement.setBinaryStream(6, bais, bytes.length);//attribute map as blob 
             statement.setString(7, data.getRowId()); //rowId
             statement.executeUpdate();
             
             data.setLastSaved(now);
             if (Log.isDebugEnabled())
                 Log.debug("Updated session "+data);
         }
         finally
         {
             if (connection!=null)
                 connection.close();
         }
     }
     
     
     /**
      * Update the node on which the session was last seen to be my node.
      * 
      * @param data
      * @throws Exception
      */
     protected void updateSessionNode (SessionData data)
     throws Exception
     {
         String nodeId = getSessionIdManager().getWorkerName();
         Connection connection = getConnection();
         PreparedStatement statement = null;
         try
         {            
             connection.setAutoCommit(true);
             statement = connection.prepareStatement(__updateSessionNode);
             statement.setString(1, nodeId);
             statement.setString(2, data.getRowId());
             statement.executeUpdate();
             statement.close();
             if (Log.isDebugEnabled())
                 Log.debug("Updated last node for session id="+data.getId()+", lastNode = "+nodeId);
         }
         finally
         {
             if (connection!=null)
                 connection.close();
         }
     }
     
     /**
      * Persist the time the session was last accessed.
      * 
      * @param data
      * @throws Exception
      */
     private void updateSessionAccessTime (SessionData data)
     throws Exception
     {
         Connection connection = getConnection();
         PreparedStatement statement = null;
         try
         {            
             long now = System.currentTimeMillis();
             connection.setAutoCommit(true);
             statement = connection.prepareStatement(__updateSessionAccessTime);
             statement.setString(1, getSessionIdManager().getWorkerName());
             statement.setLong(2, data.getAccessed());
             statement.setLong(3, data.getLastAccessed());
             statement.setLong(4, now);
             statement.setLong(5, data.getExpiryTime());
             statement.setString(6, data.getRowId());
             statement.executeUpdate();
             data.setLastSaved(now);
             statement.close();
             if (Log.isDebugEnabled())
                 Log.debug("Updated access time session id="+data.getId());
         }
         finally
         {
             if (connection!=null)
                 connection.close();
         }
     }
     
     
     
     
     /**
      * Delete a session from the database. Should only be called
      * when the session has been invalidated.
      * 
      * @param data
      * @throws Exception
      */
     protected void deleteSession (SessionData data)
     throws Exception
     {
         Connection connection = getConnection();
         PreparedStatement statement = null;
         try
         {
             connection.setAutoCommit(true);
             statement = connection.prepareStatement(__deleteSession);
             statement.setString(1, data.getRowId());
             statement.executeUpdate();
             if (Log.isDebugEnabled())
                 Log.debug("Deleted Session "+data);
         }
         finally
         {
             if (connection!=null)
                 connection.close();
         } 
     }
     
     
     
     /**
      * Get a connection from the driver.
      * @return
      * @throws SQLException
      */
     private Connection getConnection ()
     throws SQLException
     { 
         return ((JDBCSessionIdManager)getSessionIdManager()).getConnection();
     }
 
     /**
      * Calculate a unique id for this session across the cluster.
      * 
      * Unique id is composed of: contextpath_virtualhost0_sessionid
      * @param data
      * @return
      */
     private String calculateRowId (SessionData data)
     {
         String rowId = canonicalize(_context.getContextPath());
         rowId = rowId + "_" + getVirtualHost(_context);
         rowId = rowId+"_"+data.getId();
         return rowId;
     }
     
     /**
      * Get the first virtual host for the context.
      * 
      * Used to help identify the exact session/contextPath.
      * 
      * @return 0.0.0.0 if no virtual host is defined
      */
     private String getVirtualHost (ContextHandler.Context context)
     {
         String vhost = "0.0.0.0";
         
         if (context==null)
             return vhost;
         
         String [] vhosts = context.getContextHandler().getVirtualHosts();
         if (vhosts==null || vhosts.length==0 || vhosts[0]==null)
             return vhost;
         
         return vhosts[0];
     }
     
     /**
      * Make an acceptable file name from a context path.
      * 
      * @param path
      * @return
      */
     private String canonicalize (String path)
     {
         if (path==null)
             return "";
         
         return path.replace('/', '_').replace('.','_').replace('\\','_');
     }
 }