Servlet的监听器-编程知识

Servlet常用的监听器
ServletContextAttributeListener 用来感知ServlerContext对象属性变化，比如添加或删除属性变化
ServletContextListener 用来感知ServlerContext对象的创建和销毁的
ServletRequestListener 可以用来监听感知ServletRequest对象的创建和销毁的
ServletRequestAttributeListener 用来感知ServletRequest属性变化，如何添加或删除属性还是替换
HttpSessionListener监听session的变化，常用于统计在线人数
HttpSessionAttributeListener用来监听Session属性变化
HttpSessionBindingListener 用来监听把一个数据绑定到Session对象感知监听器
HttpSessionActivationListener用来监听session绑定的对象钝化(把对象持久化磁盘)
常用的有前6个

package com.sparrow.listener;import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;/*** @Author: 诉衷情の麻雀* @Description: 当一个类实现了ServletContextListener 是一个监听器，该类可以监听的事件* 由该类实现的监听接口决定 该类可以监听ServletContext的创建和销毁* 当web应用启动时，就会产生ServletContextEvent事件,会调用监听器的对应事件处理方法contextInitialized，同时会传递事件对象* 我们可以通过ServletContextEvent事件对象，来获取需要的信息，然后再进行业务处理* 需要在web.xml配置监听器这样才能使tomcat知道，底层使用反射机制* @DateTime: 2023/7/5 9:57**/
public class SparrowServletContextListener implements ServletContextListener {@Overridepublic void contextInitialized(ServletContextEvent sce) {ServletContext servletContext = sce.getServletContext();System.out.println("SparrowServletContextListener监听到" + servletContext+ " 被创建...");//如果我们获取到ServletContext对象进行业务处理}@Overridepublic void contextDestroyed(ServletContextEvent sce) {ServletContext servletContext = sce.getServletContext();System.out.println("SparrowServletContextListener监听到" + servletContext+ " 被销毁...");//比如可以对servletContext数据进行处理 或者日志的管理System.out.println("进行处理");}
}

/*** @Author: 诉衷情の麻雀* @Description: TODO* @DateTime: 2023/7/5 10:10**/
public class SparrowServletContextAttributeListener implements ServletContextAttributeListener {@Overridepublic void attributeAdded(ServletContextAttributeEvent scae) {System.out.println("SparrowServletContextAttributeListener监听到"+ scae.getName());}@Overridepublic void attributeRemoved(ServletContextAttributeEvent scae) {System.out.println("SparrowServletContextAttributeListener监听到:" + scae.getValue());}@Overridepublic void attributeReplaced(ServletContextAttributeEvent scae) {}
}

ServletContextAttributeListener属性监听器

package com.sparrow.listener;import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;/*** @Author: 诉衷情の麻雀* @Description: TODO* @DateTime: 2023/7/5 10:10**/
public class SparrowServletContextAttributeListener implements ServletContextAttributeListener {@Overridepublic void attributeAdded(ServletContextAttributeEvent scae) {System.out.println("SparrowServletContextAttributeListener监听到添加属性:"+ scae.getName()+"=" + scae.getValue());}@Overridepublic void attributeRemoved(ServletContextAttributeEvent scae) {System.out.println("SparrowServletContextAttributeListener监听到删除属性:" + scae.getName() + "="+ scae.getValue());}@Overridepublic void attributeReplaced(ServletContextAttributeEvent scae) {System.out.println("SparrowServletContextAttributeListener监听到修改/替换属性:" + scae.getName() + "="+ scae.getValue());}
}

配置一个HelloServlet

/*** @Author: 诉衷情の麻雀* @Description: TODO* @DateTime: 2023/7/18 19:59**/
public class HelloServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doPost(req,resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("helloServlet被调用了");ServletContext servletContext = req.getServletContext();servletContext.setAttribute("name", "诉衷情の麻雀");servletContext.setAttribute("name", "诉衷情の麻雀");servletContext.removeAttribute("name");}
}

   <servlet><servlet-name>HelloServlet</servlet-name><servlet-class>com.sparrow.servlet.HelloServlet</servlet-class></servlet><servlet-mapping><servlet-name>HelloServlet</servlet-name><url-pattern>/helloServlet</url-pattern></servlet-mapping>

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HttpSessionListener

/*** @Author: 诉衷情の麻雀* @Description: TODO* @DateTime: 2023/7/5 10:25**/
public class SparrowHttpSessionListener implements HttpSessionListener {@Overridepublic void sessionCreated(HttpSessionEvent se) {HttpSession session = se.getSession();//当session创建时设置一个生命周期session.setMaxInactiveInterval(30);System.out.println("SparrowHttpSessionListener监听到session创建= " + session.getId());}@Overridepublic void sessionDestroyed(HttpSessionEvent se) {HttpSession session = se.getSession();System.out.println("SparrowHttpSessionListener监听到session销毁= " + session.getId());}
}

 @Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//获取sessionHttpSession session = req.getSession(); //如果没有就创建}

配置监听器

 <!--配置监听器--><listener><listener-class>com.sparrow.listener.SparrowHttpSessionListener</listener-class></listener><listener><listener-class>com.sparrow.listener.SparrowServletContextListener</listener-class></listener><listener><listener-class>com.sparrow.listener.SparrowServletContextAttributeListener</listener-class></listener><listener><listener-class>com.sparrow.listener.SparrowRequestListener</listener-class></listener>

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HttpSessionAttributeListener

package com.sparrow.listener;import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;/**
* @Author: 诉衷情の麻雀
* @Description: TODO
* @DateTime: 2023/7/18 20:26
**/
public class SparrowHttpSessionAttributeListener implements HttpSessionAttributeListener {@Overridepublic void attributeAdded(HttpSessionBindingEvent se) {System.out.println("SparrowHttpSessionAttributeListener 监听到session添加属性了" + se.getName() + "=" + se.getValue() );}@Overridepublic void attributeRemoved(HttpSessionBindingEvent se) {System.out.println("SparrowHttpSessionAttributeListener 监听到session删除属性了" + se.getName());}@Overridepublic void attributeReplaced(HttpSessionBindingEvent se) {System.out.println("SparrowHttpSessionAttributeListener 监听到session修改属性了" + se.getName() + "=" + se.getValue() );}
}

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ServletRequestListener监听器

作用：监听Request对象的创建和销毁
常用于监控某个IP访问网站频率/用户访问的页面、资源(日志)

public class SparrowRequestListener implements ServletRequestListener {@Overridepublic void requestInitialized(ServletRequestEvent sre) {System.out.println("监听到request对象创建");ServletRequest servletRequest = sre.getServletRequest();System.out.println("访问IP=" + servletRequest.getRemoteAddr());System.out.println("访问的资源=" + ((HttpServletRequest) servletRequest).getRequestURL());}@Overridepublic void requestDestroyed(ServletRequestEvent sre) {System.out.println("监听到request对象被销毁");}
}

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ServletRequestAttributeListener监听器

作用：监听Request属性变化

public class SparrowRequestAttributeListener implements ServletRequestAttributeListener {@Overridepublic void attributeAdded(ServletRequestAttributeEvent srae) {}@Overridepublic void attributeRemoved(ServletRequestAttributeEvent srae) {ServletRequestAttributeListener.super.attributeRemoved(srae);}@Overridepublic void attributeReplaced(ServletRequestAttributeEvent srae) {ServletRequestAttributeListener.super.attributeReplaced(srae);}
}