characterEncodingFilter作用

package com.demo.test;

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;

public class characterEncodingFilter implements Filter {

    
    private String characterEncoding;
    private boolean enabled;
    public void destroy() {
        // TODO Auto-generated method stub
        characterEncoding = null;//销毁时清空资源
    }

    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        if(enabled || characterEncoding != null){//如果启用该Filter
            request.setCharacterEncoding(characterEncoding);//设置reques编码
            response.setCharacterEncoding(characterEncoding);//设置response编码
        }
        chain.doFilter(request,response );//doFilter,执行下一个Filter或者Servlet
    }

    public void init(FilterConfig config) throws ServletException {//初始化时加载参数
        // TODO Auto-generated method stub
        characterEncoding = config.getInitParameter(characterEncoding);//编码方式
        enabled = "true".equalsIgnoreCase(config.getInitParameter("enabled").trim());//启用
    }
  
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <display-name></display-name>    
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <filter>
    <filter-name>characterEncodingFilter</filter-name>
    <filter-class>com.helloweenvsfei.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>characterEncoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
      <param-name>enabled</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>characterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>