字符编码的过滤器Filter（即输入的汉字，能在页面上正常显示，不会出现乱码）

时间：2022-02-17 09:56:05

自定义抽象的 HttpFilter类, 实现自 Filter 接口

package com.lanqiao.javaweb;

import java.io.IOException;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 // 自定义的 HttpFilter, 实现自 Filter 接口

public abstract class HttpFilter implements Filter {

     // 用于保存 FilterConfig 对象. 

    private FilterConfig filterConfig;

     // 不建议子类直接覆盖. 若直接覆盖, 将可能会导致 filterConfig 成员变量初始化失败

    @Override

    public void init(FilterConfig filterConfig) throws ServletException {

        this.filterConfig = filterConfig;

        init();

    }

     //供子类继承的初始化方法. 可以通过 getFilterConfig() 获取 FilterConfig 对象.

    protected void init() {}

     // 直接返回 init(ServletConfig) 的 FilterConfig 对象

    public FilterConfig getFilterConfig() {

        return filterConfig;

    }

    /**

     * 原生的 doFilter 方法, 在方法内部把 ServletRequest 和 ServletResponse

     * 转为了 HttpServletRequest 和 HttpServletResponse, 并调用了

     * doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)

     *

     * 若编写 Filter 的过滤方法不建议直接继承该方法. 而建议继承

     * doFilter(HttpServletRequest request, HttpServletResponse response,

     *        FilterChain filterChain) 方法

     */

    @Override

    public void doFilter(ServletRequest req, ServletResponse resp,

            FilterChain chain) throws IOException, ServletException {

        HttpServletRequest request = (HttpServletRequest) req;

        HttpServletResponse response = (HttpServletResponse) resp;

        doFilter(request, response, chain);

    }

    //抽象方法, 为 Http 请求定制. 必须实现的方法. 

    public abstract void doFilter(HttpServletRequest request, HttpServletResponse response,

            FilterChain filterChain) throws IOException, ServletException;

    //空的 destroy 方法。

    @Override

    public void destroy() {}

}

建立一个Filter类，其继承于父类HttpFilter

package com.atguigu.javaweb.encoding;

import java.io.IOException;

import javax.servlet.FilterChain;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import com.atguigu.javaweb.HttpFilter;

public class EncodingFilter extends HttpFilter{

　　//配置参数

    private String encoding;

    @Override
　　//获取web.jsp文件里配置和映射里的encoding属性

    protected void init() {

        encoding = getFilterConfig().getServletContext().getInitParameter("encoding");

    }

    @Override

    public void doFilter(HttpServletRequest request,HttpServletResponse response, FilterChain filterChain) throws IOException, ServletException {

        //System.out.println(encoding);

        request.setCharacterEncoding(encoding);

        filterChain.doFilter(request, response);

    }

}

WEB-INF下的web.xml文件的配置：

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

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">

  <filter>

      <filter-name>encodingFilter</filter-name>

      <filter-class>com.lanqiao.javatest.encoding.EncodingFilter</filter-class>

  </filter>

  <filter-mapping>

      <filter-name>encodingFilter</filter-name>

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

  </filter-mapping>

　　<context-param>
　　　　<param-name>encoding</param-name>
　　　　<param-value>UTF-8</param-value>
　　</context-param>

</web-app>

在WebContent下的encoding文件里的login.jsp和index.jsp页面：

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

    pageEncoding="UTF-8"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>Insert title here</title>

</head>

<body>

    <form action="login.jsp" method="post">

        username:<input type="text" name="username"/><br><br>

        <input type="submit" name="tt" />

    </form>

</body>

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

    pageEncoding="UTF-8"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>Insert title here</title>

</head>

<body>

    hello:${param.username }

</body>

</html>

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