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java项目实践-jsp-finter-监听器-day19

时间：2023-10-21 12:22:16浏览次数：36  
标签：java void http finter javax 监听器 import servlet public

目录

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>

登录 http://localhost:8080/learningfilter/serv2.do 则调到 login.jsp

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.
      */
    }
}

标签：java,void,http,finter,javax,监听器,import,servlet,public
From： https://www.cnblogs.com/cavalier-chen/p/17778774.html

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