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JavaWeb_09_Filter过滤器

知年_7740 2022-03-11 阅读 90
javamysqlmaven

JavaWeb_09_Filter过滤器

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P24 过滤器Filter（重点）

Filter：过滤器，用来过滤网站的数据；

  • 处理中文乱码
  • 登录验证…

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Filter开发步骤：

  1. 导包不要导错
    在这里插入图片描述
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.niumo</groupId>
    <artifactId>javaweb-filter</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- Servlet 依赖 -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
        </dependency>

        <!-- JSP依赖 -->
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.2</version>
        </dependency>

        <!-- JSTL表达式的依赖 -->
        <dependency>
            <groupId>javax.servlet.jsp.jstl</groupId>
            <artifactId>jstl-api</artifactId>
            <version>1.2</version>
        </dependency>

        <!-- standard标签库 -->
        <dependency>
            <groupId>taglibs</groupId>
            <artifactId>standard</artifactId>
            <version>1.1.2</version>
        </dependency>

        <!-- 连接数据库 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.28</version>
        </dependency>

    </dependencies>

</project>

  1. 实现Filter接口，重写对应的方法即可

    package com.niumo.filter;

import javax.servlet.*;
import java.io.IOException;

public class CharacterEncodingFilter implements Filter {

    //初始化：web服务器启动，就已经初始化了，随时等待过滤对象出现！
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter初始化");
    }

    //filterChain：链
    /*
    1. 过滤器中的所有代码，在过滤特定请求的时候都会执行
    2. 必须要让过滤器继续通行
        filterChain.doFilter(servletRequest,servletResponse);
    * */
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=UTF-8");

        System.out.println("CharacterEncodingFilter执行前...");
        filterChain.doFilter(servletRequest,servletResponse); //让我们的请求继续走，如果不写，程序到这里就被拦截停止！
        System.out.println("CharacterEncodingFilter执行后...");
    }

    //销毁：web服务器关闭的时候，过滤器会销毁
    public void destroy() {
        System.out.println("CharacterEncodingFilter销毁");
    }
}

    package com.niumo.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ShowServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        resp.setCharacterEncoding("utf-8");
//        resp.setHeader("Content-Type","text/html;charset=UTF-8");
        resp.getWriter().write("你好呀，牛魔瘦了！");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

  2. 在web.xml中配置Filter

    <?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">
    
    <servlet>
        <servlet-name>ShowServlet</servlet-name>
        <servlet-class>com.niumo.servlet.ShowServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/servlet/show</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/show</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.niumo.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <!--只要是/servlet的任何请求，会经过这个过滤器-->
        <url-pattern>/servlet/*</url-pattern>
        <!--<url-pattern>/*</url-pattern>-->
    </filter-mapping>

</web-app>

P27 Filter实现权限拦截

用户登录之后才能进入主页！用户注销后就不能进入主页了！

  1. 用户登录之后，向Session中放入用户的数据
  2. 进入主页的时候要判断用户是否已经登录；要求：在过滤器中实现！
  • 登录页面：Login.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<h1>登录</h1>

<form action="/servlet/login" method="post">
    <input type="text" name="username">
    <input type="submit">
</form>

</body>
</html>
  • LoginServlet.java
package com.niumo.servlet;

import com.niumo.util.Constant;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class LoginServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //获取前端请求的参数
        String username = req.getParameter("username");

        if(username.equals("admin")){ //登录成功
            req.getSession().setAttribute(Constant.USER_SESSION,req.getSession().getId());
            resp.sendRedirect("/sys/success.jsp");
        }else { //登录失败
            resp.sendRedirect("/error.jsp");
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}
  • web.xml
    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>com.niumo.servlet.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/servlet/login</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>LogoutServlet</servlet-name>
        <servlet-class>com.niumo.servlet.LogoutServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LogoutServlet</servlet-name>
        <url-pattern>/servlet/logout</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>SysFilter</filter-name>
        <filter-class>com.niumo.filter.SysFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>SysFilter</filter-name>
        <url-pattern>/sys/*</url-pattern>
    </filter-mapping>
  • 登录成功页面：/sys/success.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<h1>主页</h1>

<p><a href="/servlet/logout">注销</a></p>

</body>
</html>
  • 登录失败页面：error.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>错误</h1>
<h3>没有权限，用户名错误</h3>

<a href="/Login.jsp">返回登录页面</a>

</body>
</html>
  • 过滤器：SysFilter.java
package com.niumo.filter;

import com.niumo.util.Constant;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class SysFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

        // ServletRequest   HttpServletRequest
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;

        if(request.getSession().getAttribute(Constant.USER_SESSION)==null){
            response.sendRedirect("/error.jsp");
        }

        filterChain.doFilter(servletRequest,servletResponse);

        /*
            if(request.getSession().getAttribute(Constant.USER_SESSION).level==VIP1){
                response.sendRedirect("vip1/index.jsp");
            }
                    if(request.getSession().getAttribute(Constant.USER_SESSION).level==VIP2){
                response.sendRedirect("vip2/index.jsp");
            }
            if(request.getSession().getAttribute(Constant.USER_SESSION).level==VIP3){
                response.sendRedirect("vip3/index.jsp");
            }
         */

    }

    public void destroy() {

    }
}
  • 常量：Constant.java
package com.niumo.util;

public class Constant {
    public final static String USER_SESSION = "USER_SESSION";
}

/*
User
    id
    name
    level   等级

VIP1
VIP2
VIP3
VIP4
* */
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