java项目实践-jsp-filter-监听器-day19

1. jsp
2. 过滤器
3. listener 监听器

1. jsp

servle逻辑处理方便 html页面表现麻烦

jsp 页面表现方便但是逻辑处理麻烦

JSP

是一种页面技术 JSP本质上是servlet类通过JSP引擎翻译成servlet

jsp 约等于 java+html

注意：jsp不是访问静态的html文件

index.jsp修改成如下代码：

<%--

  Created by IntelliJ IDEA.

  User: chenw

  Date: 2023/10/19

  Time: 22:27

  To change this template use File | Settings | File Templates.

--%>

<%@ page contentType="text/html;charset=UTF-8" language="java" import="java.util.*,java.lang.*" pageEncoding="utf-8" %>

<html>

  <head>

    <title>$Title$</title>

  </head>

  <body>

  <%

    int i = new Random().nextInt(10);

    if(i>5){

  %>

  <b>今天天气很好 ！</b>

  <%}else{

  %>

  <b>今天天气不好~~</b>

  <%}%>

  </body>

</html>

2. 过滤器

作用：

分析请求对请求的数据进行预处理

阻止请求的进行

web资源的协作

修改请求他的内容

servlet1

response.getWriter().write("学习 filter1");

servlet2

response.getWriter().write("学习 filter2");

启服务访问

http://localhost:8080/learningfilter/serv1

http://localhost:8080/learningfilter/serv2

都会有乱码

如何用filter解决

new filter

web.xml增加如下配置

    <filter>

        <filter-name>SetEncodingFilter</filter-name>

        <filter-class>com.msb.filter.SetEncodingFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>SetEncodingFilter</filter-name>

        <url-pattern>/*</url-pattern>

    </filter-mapping>

所有的请求都需要经过 SetEncodingFilter处理

public class SetEncodingFilter implements Filter {

    public void destroy() {

    }

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {

        req.setCharacterEncoding("utf-8");

        resp.setContentType("text/html;charset=utf-8");

        chain.doFilter(req, resp);

    }

    public void init(FilterConfig config) throws ServletException {

    }

}

没有中文乱码了

用过滤启来做一个登录拦截条件是session里面含有user

LoginFilter

package com.msb.filter;

import javax.servlet.*;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

import java.io.IOException;

/**

 * @Auther: jack.chen

 * @Date: 2023/10/21 - 10 - 21 - 10:36

 * @Description: ${PACKAGE_NAME}

 * @version: 1.0

 */

public class LoginFilter implements Filter {

    public void destroy() {

    }

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {

        HttpSession session = ((HttpServletRequest)req).getSession();

        if(session.getAttribute("user") == null){

            ((HttpServletResponse)resp).sendRedirect("login.jsp");

        }else{

            chain.doFilter(req, resp);

        }

    }

    public void init(FilterConfig config) throws ServletException {

    }

}

web.xml配置

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"

         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"

         version="4.0">

    <filter>

        <filter-name>SetEncodingFilter</filter-name>

        <filter-class>com.msb.filter.SetEncodingFilter</filter-class>

    </filter>

    <filter>

        <filter-name>LoginFilter</filter-name>

        <filter-class>com.msb.filter.LoginFilter</filter-class>

    </filter>

    <filter-mapping>

        <filter-name>LoginFilter</filter-name>

        <url-pattern>*.do</url-pattern>

    </filter-mapping>

    <filter-mapping>

        <filter-name>SetEncodingFilter</filter-name>

        <url-pattern>/*</url-pattern>

    </filter-mapping>

    <servlet>

        <servlet-name>LearningServlet1</servlet-name>

        <servlet-class>com.msb.servlet.LearningServlet1</servlet-class>

    </servlet>

    <servlet>

        <servlet-name>LearningServlet2</servlet-name>

        <servlet-class>com.msb.servlet.LearningServlet2</servlet-class>

    </servlet>

    <servlet-mapping>

        <servlet-name>LearningServlet1</servlet-name>

        <url-pattern>/serv1</url-pattern>

    </servlet-mapping>

    <servlet-mapping>

        <servlet-name>LearningServlet2</servlet-name>

        <url-pattern>/serv2.do</url-pattern>

    </servlet-mapping>

</web-app>

再次登录

http://localhost:8080/learningfilter/serv2.do

响应正常

3. listener 监听器

监听器的作用：

监听一些共享对象属性值的变化或者事件的发生前后做出响应的响应类似触发器

这些共享对象有：

ServletContext 对象全局唯一的tomcat启动时创建停止时销毁

HttpSession对象

ServletRequest 对象

servlet

package com.msb.servlet;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

import java.io.IOException;

/**

 * @Auther: jack.chen

 * @Date: 2023/10/21 - 10 - 21 - 11:40

 * @Description: ${PACKAGE_NAME}

 * @version: 1.0

 */

public class ListenerServlet extends HttpServlet {

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        request.setCharacterEncoding("utf-8");

        response.setContentType("text/html;charset=utf-8");

        // request对象设置属性

        request.setAttribute("learning", "listener");

        //servletContext对象添加属性

        ServletContext context = this.getServletContext();

        context.setAttribute("servlet_key", "servlet_value");

        // 设置session

        HttpSession session = request.getSession();

        session.setAttribute("sess_key", "sess_value");

        response.getWriter().write("Learning Listener !");

    }

}

listener

package com.msb.listener; /**

 * @Auther: jack.chen

 * @Date: 2023/10/21 - 10 - 21 - 11:45

 * @Description: ${PACKAGE_NAME}

 * @version: 1.0

 */

import javax.servlet.*;

import javax.servlet.http.HttpSessionAttributeListener;

import javax.servlet.http.HttpSessionEvent;

import javax.servlet.http.HttpSessionListener;

import javax.servlet.http.HttpSessionBindingEvent;

public class MyListener1 implements ServletRequestListener, ServletRequestAttributeListener,

        ServletContextListener, ServletContextAttributeListener,

        HttpSessionListener, HttpSessionAttributeListener

{

    @Override

    public void attributeAdded(ServletRequestAttributeEvent servletRequestAttributeEvent) {

        // request对象 属性增加

        // 将设置的属性打印

        System.out.println(servletRequestAttributeEvent.getName());

        System.out.println(servletRequestAttributeEvent.getValue());

    }

    @Override

    public void attributeRemoved(ServletRequestAttributeEvent servletRequestAttributeEvent) {

        // request对象 属性移除

    }

    @Override

    public void attributeReplaced(ServletRequestAttributeEvent servletRequestAttributeEvent) {

        // request对象 属性重新设置

        // 将设置的属性打印

        System.out.println(servletRequestAttributeEvent.getName());

        System.out.println(servletRequestAttributeEvent.getValue());

    }

    @Override

    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {

        // request对象 创建

    }

    @Override

    public void requestInitialized(ServletRequestEvent servletRequestEvent) {

        // request对象 销毁

    }

    @Override

    public void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {

        // servletContext 对象添加属性

    }

    @Override

    public void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {

        // servletContext 对象移除属性

    }

    @Override

    public void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {

        // servletContext 对象 替换属性

    }

    @Override

    public void contextInitialized(ServletContextEvent servletContextEvent) {

        //  servletContext 对象创建  tomcat启动时创建一次 全局共享

    }

    @Override

    public void contextDestroyed(ServletContextEvent servletContextEvent) {

        //  servletContext 停止时销毁

    }

    @Override

    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {

        // session 对象 添加属性

    }

    @Override

    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {

        // session 对象 移除属性

    }

    @Override

    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {

        // session 对象 修改属性

    }

    @Override

    public void sessionCreated(HttpSessionEvent httpSessionEvent) {

        // session 对象被创建

    }

    @Override

    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {

        // session 对象销毁

    }

}

web.xml

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"

         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"

         version="4.0">

    <listener>

        <listener-class>com.msb.listener.MyListener1</listener-class>

    </listener>

    <servlet>

        <servlet-name>ListenerServlet</servlet-name>

        <servlet-class>com.msb.servlet.ListenerServlet</servlet-class>

    </servlet>

    <servlet-mapping>

        <servlet-name>ListenerServlet</servlet-name>

        <url-pattern>/serv1</url-pattern>

    </servlet-mapping>

</web-app>

用listener实现在线人数的统计

不同的浏览器分别访问

page.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<html>

<head>

    <title>Title</title>

</head>

<body>

当前在线人数：${applicationScope.count}

</body>

</html>

listener

package com.msb.listener; /**

 * @Auther: jack.chen

 * @Date: 2023/10/21 - 10 - 21 - 12:07

 * @Description: ${PACKAGE_NAME}

 * @version: 1.0

 */

import javax.servlet.ServletContext;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

import javax.servlet.http.HttpSessionAttributeListener;

import javax.servlet.http.HttpSessionEvent;

import javax.servlet.http.HttpSessionListener;

import javax.servlet.http.HttpSessionBindingEvent;

public class CountListener implements ServletContextListener,

        HttpSessionListener, HttpSessionAttributeListener {

    // Public constructor is required by servlet spec

    public CountListener() {

    }

    // -------------------------------------------------------

    // ServletContextListener implementation

    // -------------------------------------------------------

    public void contextInitialized(ServletContextEvent sce) {

      /* This method is called when the servlet context is

         initialized(when the Web application is deployed).

         You can initialize servlet context related data here.

      */

        ServletContext servletContext = sce.getServletContext();

        // 设置初始值

        servletContext.setAttribute("count", 0);

    }

    public void contextDestroyed(ServletContextEvent sce) {

      /* This method is invoked when the Servlet Context

         (the Web application) is undeployed or

         Application Server shuts down.

      */

    }

    // -------------------------------------------------------

    // HttpSessionListener implementation

    // -------------------------------------------------------

    public void sessionCreated(HttpSessionEvent se) {

        /* Session is created. */

        ServletContext servletContext = se.getSession().getServletContext();

        // 获取servletContext对象count属性

        int count = (int)servletContext.getAttribute("count");

        // +1之后设置回去

        servletContext.setAttribute("count", ++count);

    }

    public void sessionDestroyed(HttpSessionEvent se) {

        /* Session is destroyed. */

        ServletContext servletContext = se.getSession().getServletContext();

        // 获取servletContext对象count属性

        int count = (int)servletContext.getAttribute("count");

        // -1之后设置回去

        servletContext.setAttribute("count", --count);

    }

    // -------------------------------------------------------

    // HttpSessionAttributeListener implementation

    // -------------------------------------------------------

    public void attributeAdded(HttpSessionBindingEvent sbe) {

      /* This method is called when an attribute

         is added to a session.

      */

    }

    public void attributeRemoved(HttpSessionBindingEvent sbe) {

      /* This method is called when an attribute

         is removed from a session.

      */

    }

    public void attributeReplaced(HttpSessionBindingEvent sbe) {

      /* This method is invoked when an attibute

         is replaced in a session.

      */

    }

}