监听器Listener使用&Session

使用配置 xml配置

1.编写一个监听ServletContext生命周期的Listener;实现Listener接口在当前 2.项目中注册（在web.xml）使用;

public class MyServletContextListener implements ServletContextListener {
  @Override
  public void contextInitialized(ServletContextEvent sce) {
    System.out.println("this is contextInitialized");
  }

  @Override
  public void contextDestroyed(ServletContextEvent sce) {
    System.out.println("this is contextDestroyed");
  }
}

<listener>
    <listener-class>com.it.MyServletContextListener</listener-class>
</listener>

使用配置 SpringBoot 注解

1.在implements类上@WebListener Listener改为实现ServletContextListener，还要在类上加@WebListener注解。其余可以不动： 2.SpringBoot启动类配置 只需要在SpringBoot 启动类中加上@ServletComponentScan注解即可

@WebListener
public class MyServletContextListener implements ServletContextListener {
  @Override
  public void contextInitialized(ServletContextEvent sce) {
    ServletContext servletContext = sce.getServletContext();
    System.out.println("this is contextInitialized" + servletContext);
  }

  @Override
  public void contextDestroyed(ServletContextEvent sce) {
    ServletContext servletContext = sce.getServletContext();
    System.out.println("this is contextDestroyed" + servletContext);
  }
}


@ServletComponentScan
@SpringBootApplication
public class IntervienoteApplication {}

session生命周期

• 由于客户端与服务器之间的会话是无状态的机制，Session则可用于关联访问，因此多用与用户登录等功能上。

//引号中的"xxx"为页面中name标签里的值，逗号后面的是Servlet中的变量名。
request.getSession().setAttribute("xxx",xxx);//储存到session中

request.getSession().getAttribute("xxx",xxx);//读取session中的值

• 若要移除Session中特定的值，可以调用removeAttribute方法，但request中的SessionID仍不变，只是其中的值发生了改变，Session还是原来的Session

request.getSession().removeAttribute("xxx");

Attribute演示 HttpSessionAttributeListener

session.setAttribute( "user", "admin" );Thread.sleep( 3eee);
session. setAttribute( "user", "zhangsan");Thread.sleep( 3eee);
session.removeAttribute( "user");

@WebListener
public class MySession implements HttpSessionAttributeListener {
  @Override
  public void attributeAdded(HttpSessionBindingEvent se) {
	  String name = se.getName();//获取属性
	  Object value = se.getValue();//获取属性数值
	  System.out.println("session添加属性");
  }

  @Override
  public void attributeRemoved(HttpSessionBindingEvent se) {
	  System.out.println("session移除属性");
  }

  @Override
  public void attributeReplaced(HttpSessionBindingEvent se) {
	  System.out.println("session修改属性");
  }
}

Session 钝化 活化 HttpSessionActivationListener

User user = new User();
httpSession.setAttribute("loginUser", user);
@Override
public void sessionDidActivate(HttpSessionEvent se) {
	HttpSession session = se.getSession();//要钝化的session
	System.out.println("user和session一起钝化了");
}

@Override
public void sessionWillPassivate(HttpSessionEvent se) {
	System.out.println("user和session 活化来");
}

Session 綁定 解绑 HttpSessionBindingListener

@Override
User user = new User();
httpSession.setAttribute("loginUser", user);
httpSession.removeAttribute("loginUser");

// 检测user对象绑定 添加就是绑定
@Override
public void valueBound(HttpSessionBindingEvent event) {
HttpSession session = event.getSession();
Object value = event.getValue(); // 获取的绑定的数值
}

// 检测user解绑了 移除就是解绑
public void valueUnbound(HttpSessionBindingEvent event) {}

使用场景

ServletContextListener:监听服务器启动停止; HttpsessionBindingListener:监听某个对象绑定到session域中;