servlet listener

http://sakyone.iteye.com/blog/471093

Listener的作用类似于load-on-startup的Servlet,在Web应用启动时被加载,在Web应用关闭时被销毁，Listener用来作为Web应用的后台服务，比load-on-startup的Servlet更早被加载到Servlet容器中。自定义的Listener类必须实现ServletContextListener接口，并实现该接口的两个方法：contextInitialized(ServletContextEvent)和contextDestroyed(ServletContextEvent)，例如：

public class GetConnListener implements ServletContextListener{
 public void contextInitialized(ServletContextEvent sce){
  try{
   ServletContext application=sce.getServletContext();
   String driver=application.getInitParameter("driver");
   String url=application.getInitParameter("url");
   String user=application.getInitParameter("user");
   String password=application.getInitParameter("password");
   Class.forName(driver);
   Connection conn=DriverManager.getConnection(url, user, password);
   application.setAttribute("conn", conn);
  }catch(Exception e){
   System.out.println("Listener中获取数据库连接出现异常:"+e.getMessage());
  }
 }
 public void contextDestroyed(ServletContextEvent sce){
  ServletContext application=sce.getServletContext();
  Connection conn=(Connection)application.getAtrribute("conn");
  if(conn!=null){
   try{
    conn.close();
    conn=null;
   }catch(Exception e){}
  }
 }
}

Listener配置：

<listener>

  <listener-class>lee.GetConnListener</listener-class>

</listener>