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

public class SessionListener implements HttpSessionListener {
    @Override
    public void sessionCreated(HttpSessionEvent event) {
        System.out.println("创建 session 内置对象:" + event.getSession().getId());
    }
    @Override
    public void sessionDestroyed(HttpSessionEvent event) {
        System.out.println("销毁了 session 内置对象:" + event.getSession().getId());
    }
}

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

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

4.销毁 session 内置对象

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

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

1.定义 session 内置对象的属性监听器
public class SessionAttributeListener implements HttpSessionAttributeListener {
    @Override
    public void attributeAdded(HttpSessionBindingEvent event) {
        System.out.println("增加属性时候触发: " + event.getName() + ":" + event.getValue());
    }
    @Override
    public void attributeRemoved(HttpSessionBindingEvent event) {
        System.out.println("删除属性时候触发: " + event.getName() + ":" + event.getValue());
    }
    @Override
    public void attributeReplaced(HttpSessionBindingEvent event) {
        System.out.println("替换属性时候触发: " + event.getName() + ":" + event.getValue());
    }
}

2.配置 session 内置对象的属性监听器

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

3.测试监听器

@SuppressWarnings("serial")
public class EmpServlet extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        //增加属性
        session.setAttribute("name", "李四");
        //替换属性
        session.setAttribute("name", "张三");
        //删除属性
        session.removeAttribute("name");
    }
}

Demo: 访问 jsp 页面的时候为什么会触发 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 ), 之后再将源码编译成对应的*.class,
　　之后发那会给浏览器之前会被解析为 html 代码给到浏览器解析时