（重点）JavaWeb（入门篇18）过滤器Filter实现Servlet乱码问题案例

一、过滤器Filter实现Servlet乱码问题案例

1. 实现功能，

添加一个过滤器，实现所有访问 /filter/* 映射下的Servlet都
解决中文乱码问题

2.核心代码

注意一定要转释放不然其他Servlet拿不到请求。

servletRequest.setCharacterEncoding("utf-8");
servletResponse.setCharacterEncoding("utf-8");
servletResponse.setContentType("text/html;charset=UTF-8");
filterChain.doFilter(servletRequest,servletResponse);//转发给其他过滤器或者Servlet(释放)

3.框架

4.代码

文件目录

1.Filter.java 过滤器

package com.bmft.filter;

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

/**
 * 过滤器步骤
 * 1.导包：到一个正确Servlet下的包，实现 Filter
 * 2.实现方法都Filter
 * （1）实现过滤
 * （2）释放
 * 3.配置过滤器web.xml
 */
public class Filter01 implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("=====过滤器初始化=====");
    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("=====过滤开始=====");
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=UTF-8");
        filterChain.doFilter(servletRequest,servletResponse);//转发给其他过滤器或者Servlet
        System.out.println("=====转发完成，过滤结束======");
    }

    public void destroy() {
        System.out.println("====过滤器销毁=====");
    }
}

2.测试Servlet，Test01.java

package com.bmft;

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 Test01 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("<h1>半亩方塘</h1>");
    }

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

3. web.xml 映射配置

<?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">
    <servlet>
        <servlet-name>Test01</servlet-name>
        <servlet-class>com.bmft.Test01</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Test01</servlet-name>
        <url-pattern>/Test01</url-pattern>
    </servlet-mapping>
    <!--加上过滤器的映射-->
    <servlet-mapping>
        <servlet-name>Test01</servlet-name>
        <url-pattern>/filter/Test01</url-pattern>
    </servlet-mapping>
    <!--过滤器filter映射-->
    <filter>
        <filter-name>Filter01</filter-name>
        <filter-class>com.bmft.filter.Filter01</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>Filter01</filter-name>
        <!--/filter下的所有映射都将被过滤包括/filter/Test01-->
        <url-pattern>/filter/*</url-pattern>
    </filter-mapping>

</web-app>

5.页面展示

1.没有过滤的访问

2.过滤后的访问

3.控制台的输出