JFinal Druid DataSourceClosedException?报错

JFinal 1.8, druid 1.0.4

我有一个TimerTask每隔30分从数据库清除过期的session数据，结果报错

Exception in thread "ExpiresSessionService" com.jfinal.plugin.activerecord.ActiveRecordException: com.alibaba.druid.pool.DataSourceClosedException: dataSource already closed at Wed Jun 04 13:22:05 CST 2014
	at com.jfinal.plugin.activerecord.DbPro.update(DbPro.java:279)
	at com.jfinal.plugin.activerecord.DbPro.update(DbPro.java:290)
	at com.jfinal.plugin.activerecord.Db.update(Db.java:214)
	at com.power.oj.core.model.SessionModel.expiresSession(SessionModel.java:48)
	at com.power.oj.core.service.SessionService.expiresSession(SessionService.java:139)
	at com.power.oj.service.ExpiresSessionService.run(ExpiresSessionService.java:22)
	at java.util.TimerThread.mainLoop(Timer.java:555)
	at java.util.TimerThread.run(Timer.java:505)
Caused by: com.alibaba.druid.pool.DataSourceClosedException: dataSource already closed at Wed Jun 04 13:22:05 CST 2014
	at com.alibaba.druid.pool.DruidDataSource.getConnectionInternal(DruidDataSource.java:990)
	at com.alibaba.druid.pool.DruidDataSource.getConnectionDirect(DruidDataSource.java:898)
	at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4544)
	at com.alibaba.druid.filter.FilterAdapter.dataSource_getConnection(FilterAdapter.java:2724)
	at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4540)
	at com.alibaba.druid.filter.stat.StatFilter.dataSource_getConnection(StatFilter.java:661)
	at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4540)
	at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:880)
	at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:872)
	at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:97)
	at com.jfinal.plugin.activerecord.Config.getConnection(Config.java:185)
	at com.jfinal.plugin.activerecord.DbPro.update(DbPro.java:276)
	... 7 more 

代码：

public class ExpiresSessionService extends TimerTask
{

  private final static Logger log = Logger.getLogger(ExpiresSessionService.class);
  private static boolean start = false;
  private static ExpiresSessionService daemon;
  private static Timer click_timer;
  private final static long INTERVAL = 30 * 60 * 1000;

  @Override
  public void run()
  {
    int numOfExpiresSession = SessionService.me().expiresSession();
    log.info(new StringBuilder(3).append("ExpiresSessionService executed: ").append(numOfExpiresSession).append(" sessions deleted.").toString());
  }

  public static void start()
  {
    if (!start)
    {
      daemon = new ExpiresSessionService();
      click_timer = new Timer("ExpiresSessionService", true);
      click_timer.schedule(daemon, INTERVAL, INTERVAL);
      start = true;
      log.info("ExpiresSessionService started.");
    }
  }

}

public int expiresSession()
  {
    return Db.update("DELETE FROM session WHERE sessionExpires <= UNIX_TIMESTAMP()");
  }