【JavaWeb学习笔记】Filter 过滤器_com.wleibniz.filter.characterencodingfilter' 未分配到 -优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_43744037/article/details/115606723

文章目录

Filter（过滤器）

Filter（过滤器）

1、关于Filter

Filter：过滤器，用来过滤网站的数据，对数据进行提前处理。

常见应用：处理中文乱码，对登录身份进行验证…

在这里插入图片描述

2、使用过滤器处理中文乱码问题

导包，实现javax.servlet.Filter接口，重写对应的方法。

package com.haining820.filter;
import javax.servlet.*;
import java.io.IOException;

public class CharacterEncodingFilter implements Filter {
    //初始化:web服务器启动,filter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");
    }

    /*
    1.过滤器中的所有代码,在过滤特定请求时都会执行
    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");  //处理中文乱码问题

        System.out.println("CharacterEncodingFilter执行前");
        filterChain.doFilter(servletRequest, servletResponse);  //让请求继续走,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,Filter会被销毁
    public void destroy() {
        System.out.println("CharacterEncodingFilter销毁");
    }
}

在web.xml中配置 Filter

    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.haining820.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <!-- /servlet目录下的任何请求都会经过这个过滤器 -->
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>

3、使用过滤器对登录身份进行验证

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>

将USER_SESSION封装

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

登录操作的servlet层，注册路径为/servlet/login

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

        }
    }

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

登录成功界面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>

登录失败界面error.jsp

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

<h1>错误</h1>
<h1>没有权限,用户名错误</h1>
<a href="/Login.jsp">返回登录页面</a>

</body>
</html>

登出操作，注册路径为/servlet/logout

public class LogoutServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object user_session = req.getSession().getAttribute(Constant.USER_SESSION);
        if(user_session!=null) {
            req.getSession().removeAttribute(Constant.USER_SESSION);
            resp.sendRedirect("/Login.jsp");
        }else{
            resp.sendRedirect("/Login.jsp");
        }
    }

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

过滤器

public class SysFilter implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {}

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;
        if(request.getSession().getAttribute(Constant.USER_SESSION)==null){
            response.sendRedirect("/error.jsp");
        }
        filterChain.doFilter(req,resp);
    }

    public void destroy() {}
}

注册filter

    <filter>
        <filter-name>SysFilter</filter-name>
        <filter-class>com.haining820.filter.SysFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>SysFilter</filter-name>
        <!--只要是sys下的请求就要经过过滤器-->
        <url-pattern>/sys/*</url-pattern>
    </filter-mapping>