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：

     
        
            
       
        encodingFilter
             
       
        com.lanqiao.javatest.encoding.EncodingFilter
         
          
            
       
        encodingFilter
             
       
        /encoding/*
         
      
     

　　<context-param>

　　　　<param-name>encoding</param-name>

　　　　<param-value>UTF-8</param-value>

　　</context-param>

 

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"%>
             
     
              username:
      
      
      
        
              
     

<%@ page language="java" contentType="text/html; charset=UTF-8"    pageEncoding="UTF-8"%>
         hello:${param.username }