javaweb -- 7、Servlet系列之监听器+案例

今天药忘吃喽~ 2023-03-01 06:07 2阅读 0赞

**目录**

10.3.2 监听：

1、

2、 ServletRequestListener：监听request对象的创建和销毁

3、添加：ServletRequestAttributeListener：监听request作用域属性的添加，删除和更改

4、添加：ServletContextListener监听servletcontext对象的属性的添加和删除和更改

5、添加：ServletContextAttributeListener监听servletcontext对象的属性的添加和删除和更改

6、添加：HttpSessionListener监听session对象的创建和销毁

7、添加：HttpSessionAttributeListener监听session对象的创建和销毁

监听实现网站在线人数案例：

--------------------

## **10.3.2 监听：** ##

**Servlet****监听器用于监听一些重要事件的发生，监听器对象可以在事情发生前、发生后可以设置一些事件**

Servlet2.3提供了对ServletContext和HttpSession对象的状态变化的监听器，Servlet2.4则增加了对ServletRequest对象状态变化的监听器

①、ServletContext对象----监听ServletContext对象，可以使web应用得知web组件的加载和卸载等运行情况

②、HttpSession对象----监听HttpSession对象，可以使web应用了解会话期间的状态并做出反应

③、ServletRequest对象----监听ServletRequest对象，可以使web应用控制web请求的生命周期

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70][]

### **1、** ###

**web.xml文件：**

<servlet>
        <servlet-name>ListenseServlet</servlet-name>
        <servlet-class>com.mashibing.servlet.ListenseServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ListenseServlet</servlet-name>
        <url-pattern>/listense</url-pattern>
    </servlet-mapping>
    <listener>
        <listener-class>com.mashibing.listense.MyListense</listener-class>
    </listener>
    <listener>
        <listener-class>com.mashibing.listense.MyListense2</listener-class>
    </listener>

**java****文件：****ListenseServlet****（监听程序）**

public class ListenseServlet extends HttpServlet {
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            this.doGet(request,response);
        }
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            
            request.setCharacterEncoding("utf-8");
            response.setContentType("text/html;charset=utf-8");
    
            System.out.println("listenseservlet逻辑处理");
            request.setAttribute("listense","listense");
            request.removeAttribute("listense"); //被删除的数据（不显示）
    ========================== 下面对应的5 ===========================
    //向servletcontext中添加属值        
            ServletContext sc = this.getServletContext();
            sc.setAttribute("servletContext","servletContext--value");
    ========================= 对应下面的6、7 =========================
    //向session作用域中添加属性
            HttpSession session = request.getSession();
            session.setAttribute("session","session--value");
            session.invalidate();
    =====================================================================
            response.getWriter().write("listense study");
        }
    }

分为：（通过绿色填充标记）

1、request接口

2、servletcontext接口

3、Session接口

### **2****、**ServletRequestListener：监听request对象的创建和销毁 ###

**java****文件：****MyListense****（监听器）**

public class MyListense implements ServletRequestListener,
    ServletRequestAttributeListener,
    ServletContextListener,
    ServletContextAttributeListener,
    HttpSessionListener,
    HttpSessionAttributeListener
     {
    //请求销毁（request对象销毁时添加的逻辑代码）
        @Override
        public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
            System.out.println("request对象被销毁---" + new Date());
        }
    //请求创建（reques对象创建时添加的逻辑代码）
        @Override
        public void requestInitialized(ServletRequestEvent servletRequestEvent) {
            System.out.println("request对象被创建---"+new Date());
        }

**web.xml****文件：**

<listener>
        <listener-class>com.mashibing.listense.MyListense2</listener-class>
    </listener>

![20200722154224529.png][]![20200722154226479.png][]

### **3、添加：**ServletRequestAttributeListener：监听request作用域属性的添加，删除和更改 ###

**java文件：****MyListense****（监听器）**

![20200722154236678.png][]

//添加属性（属性添加时要做的事情）
        @Override
        public void attributeAdded(ServletRequestAttributeEvent servletRequestAttributeEvent) {
            System.out.println("向request作用域添加数据");
            System.out.println(servletRequestAttributeEvent.getName());
            System.out.println(servletRequestAttributeEvent.getValue());
        }
    //删除属性（属性删除时要做的事情）
        @Override
        public void attributeRemoved(ServletRequestAttributeEvent servletRequestAttributeEvent) {
            System.out.println("request作用域删除数据");
            System.out.println(servletRequestAttributeEvent.getName());
            System.out.println(servletRequestAttributeEvent.getValue());
        }
    //替换属性（属性更改时要做的事情）
        @Override
        public void attributeReplaced(ServletRequestAttributeEvent servletRequestAttributeEvent) {
            System.out.println("request作用域属性替换");
            System.out.println(servletRequestAttributeEvent.getName());
            System.out.println(servletRequestAttributeEvent.getValue());
        }

![20200722154252296.png][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 1][]

### **4****、****添加：**ServletContextListener监听servletcontext对象的属性的添加和删除和更改 ###

![20200722154324338.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 2][]

**java文件：****MyListense****（监听器**

//创建属性（当启动tomcat服务器的时候创建）
        @Override
        public void contextInitialized(ServletContextEvent servletContextEvent) {
            System.out.println("servletContext创建");
        }
    //销毁属性（关闭tomcat服务器的时候销毁）
        @Override
        public void contextDestroyed(ServletContextEvent servletContextEvent) {
            System.out.println("servletContext销毁");
        }

下面都是关闭两个无关的：![20200722154440790.png][]![20200722154442511.png][]

![20200722154445452.png][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 3][]

//关闭之后：![20200722154454142.png][]

### **5、****添加：**ServletContextAttributeListener监听servletcontext对象的属性的添加和删除和更改 ###

**java****文件：****MyListense****（监听器）**

//添加属性
        @Override
        public void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {
            System.out.println("servletContext添加属性");
            System.out.println(servletContextAttributeEvent.getName());
            System.out.println(servletContextAttributeEvent.getValue());
        }
    //删除属性
        @Override
        public void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {
            System.out.println("servletContext删除属性");
            System.out.println(servletContextAttributeEvent.getName());
            System.out.println(servletContextAttributeEvent.getValue());
        }
    //修改属性
        @Override
        public void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {
            System.out.println("servletContext修改属性");
            System.out.println(servletContextAttributeEvent.getName());
            System.out.println(servletContextAttributeEvent.getValue());
        }

![20200722154529700.png][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 4][]

### **6、**添加：HttpSessionListener监听session对象的创建和销毁 ###

**java****文件：****MyListense****（监听器）**

（session对象创建的时候执行）
        @Override
        public void sessionCreated(HttpSessionEvent httpSessionEvent) {
            System.out.println("session对象被创建");
        }
    （session对象销毁的时候执行）
        @Override
        public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
            System.out.println("session对象被销毁");
        }

![20200722154606490.png][]![20200722154608352.png][]

### **7****、** 添加：HttpSessionAttributeListener监听session对象的创建和销毁 ###

**java文件：****MyListense****（监听器）**

（添加属性时被调用）
        @Override
        public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {
            System.out.println("session添加属性");
            System.out.println(httpSessionBindingEvent.getName());
            System.out.println(httpSessionBindingEvent.getValue());
        }
    （删除属性时被调用）
        @Override
        public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {
            System.out.println("session删除属性");
            System.out.println(httpSessionBindingEvent.getName());
            System.out.println(httpSessionBindingEvent.getValue());
        }
    （修改属性时被调用）
        @Override
        public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {
            System.out.println("session修改属性");
            System.out.println(httpSessionBindingEvent.getName());
            System.out.println(httpSessionBindingEvent.getValue());
        }
    }

![20200722154640937.png][]![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 5][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTA0MjU2OQ_size_16_color_FFFFFF_t_70 6][]

### **监听实现网站在线人数案例：** ###

**java****文件：****MyListense2****（监听器2）**

public class MyListense2 implements HttpSessionListener,ServletContextListener {
        @Override//创建属性（当启动tomcat服务器的时候创建）
        public void contextInitialized(ServletContextEvent servletContextEvent) {
    //获取application
            ServletContext sc = servletContextEvent.getServletContext();
    //设置网站在线人数的初始值
            sc.setAttribute("count",0);
        }
        @Override//销毁属性（关闭tomcat服务器的时候销毁）
        public void contextDestroyed(ServletContextEvent servletContextEvent) {
            System.out.println("servletContext被销毁");
        }
        @Override（session对象创建的时候执行）
        public void sessionCreated(HttpSessionEvent httpSessionEvent) {
    //获取application对象
           ServletContext sc =  httpSessionEvent.getSession().getServletContext();
            int count = (int)sc.getAttribute("count"); //强制转换
            sc.setAttribute("count",++count);
        }
        @Override（session对象销毁的时候执行）
        public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
    //获取application对象
            ServletContext sc =  httpSessionEvent.getSession().getServletContext();
            int count = (int)sc.getAttribute("count"); //强制转换
            sc.setAttribute("count",--count);
        }
    }

**jsp****文件：****main**

**添加：**

<body>
    当前在线的人数是：${applicationScope.count}
    </body>

**web.xml****文件：**

<listener>
      <listener-class>com.mashibing.listense.MyListense2</listener-class>
    </listener>

![20200722154807263.png][]

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[20200722154236678.png]: https://img-blog.csdnimg.cn/20200722154236678.png
[20200722154252296.png]: https://img-blog.csdnimg.cn/20200722154252296.png
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