java基础-filter

package com.bjpowernode.drp.util.filter;  
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;  
/**  
 * 采用Filter统一处理字符集  
 * @author Administrator  
 *  
 */  
public class CharsetEncodingFilter implements Filter {  
    private String encoding;   
    public void destroy() {  
    }  
    public void doFilter(ServletRequest request, ServletResponse response,  
            FilterChain chain) throws IOException, ServletException {  
        System.out.print("刚刚进来");     
        //设置字符集  
        request.setCharacterEncoding("GB18030");  
        //继续执行  
        chain.doFilter(request, response);  
        System.out.print("好了，结束了");  
    }  
    /**  
     * @param filterConfig可以用来读取filter里头的参数  
     */  
    public void init(FilterConfig filterConfig) throws ServletException {  
        this.encoding = filterConfig.getInitParameter("encoding");  
        System.out.print("encoding"+encoding);  
    }  
}  

<?xml version="1.0" encoding="UTF-8"?>  
<web-app version="2.4"   
    xmlns="http://java.sun.com/xml/ns/j2ee"   
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee   
    http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">  
  <display-name></display-name>    
<!--   告诉tomcat去找那个filter -->  
  <filter>  
    <filter-name>CharsetEncodingFilter</filter-name>  
<filter-class>com.bjpowernode.drp.util.filter.CharsetEncodingFilter</filter-class>  
    <!-- 在filter里头传入参数 -->  
    <init-param>  
        <param-name>encoding</param-name>  
        <param-value>GBK</param-value>  
    </init-param>  
  </filter>  
<!--  告诉哪个filter对哪些个servlet起作用  -->  
  <filter-mapping>  
    <filter-name>CharsetEncodingFilter</filter-name>  
    <url-pattern>*.jsp</url-pattern>  
  </filter-mapping>  
</web-app>