Session监听器

Session 内置对象的监听器

Demo: 监听 session 的状态
1.定义 session 内置对象的状态监听器

 1 public class SessionListener implements HttpSessionListener {  2  @Override  3     public void sessionCreated(HttpSessionEvent event) {  4         System.out.println("建立 session 内置对象:" + event.getSession().getId());  5  }  6  @Override  7     public void sessionDestroyed(HttpSessionEvent event) {  8         System.out.println("销毁了 session 内置对象:" + event.getSession().getId());  9  } 10 }

2.配置 session 内置对象的状态监听器

<listener>
      <listener-class>com.sxt.mvcpro.listener.SessionListener</listener-class>
  </listener>

3.获取 session 内置对象

1 @SuppressWarnings("serial") 2 public class EmpServlet extends HttpServlet{ 3  @Override 4     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 5  req.getSession(); 6         System.out.println("访问了 servlet 方法"); 7  } 8 }

4.销毁 session 内置对象

1 @SuppressWarnings("serial") 2 public class EmpServlet extends HttpServlet{ 3  @Override 4     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 5  req.getSession().invalidate(); 6  } 7 }

Demo: 监听 session 的属性
1.定义 session 内置对象的属性监听器

 1 1.定义 session 内置对象的属性监听器  2 public class SessionAttributeListener implements HttpSessionAttributeListener {  3  @Override  4     public void attributeAdded(HttpSessionBindingEvent event) {  5         System.out.println("增长属性时候触发: " + event.getName() + ":" + event.getValue());  6  }  7  @Override  8     public void attributeRemoved(HttpSessionBindingEvent event) {  9         System.out.println("删除属性时候触发: " + event.getName() + ":" + event.getValue()); 10  } 11  @Override 12     public void attributeReplaced(HttpSessionBindingEvent event) { 13         System.out.println("替换属性时候触发: " + event.getName() + ":" + event.getValue()); 14  } 15 }

2.配置 session 内置对象的属性监听器

1   <listener>
2       <listener-class>com.sxt.mvcpro.listener.SessionAttributeListener</listener-class>
3   </listener>

3.测试监听器

 1 @SuppressWarnings("serial")  2 public class EmpServlet extends HttpServlet{  3  @Override  4     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {  5         HttpSession session = req.getSession();  6         //增长属性
 7         session.setAttribute("name", "李四");  8         //替换属性
 9         session.setAttribute("name", "张三"); 10         //删除属性
11         session.removeAttribute("name"); 12  } 13 }

Demo: 访问 jsp 页面的时候为何会触发 sessionCreated 方法?
　　访问 jsp 页面的时候容器会将 jsp 页面转换成一个特殊的 Servlet,
　　先将其转换为对应的*.java 源码(源码会调用sessionCreated ), 以后再将源码编译成对应的*.class,
　　以后发那会给浏览器以前会被解析为 html 代码给到浏览器解析时