用过滤器来解决JSP中文乱码问题

首先写一个过滤器的类，如下：

package com.util;

import java.io.IOException;
import java.io.UnsupportedEncodingException;

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.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;


//过滤器处理表单传到servlet的乱码问题
public class MyFilter implements Filter{
    //自写一个request换掉原来的request,重写里面的getParemeter方法，可以设置编码
    class MyRequest extends HttpServletRequestWrapper{
        
        @Override
        public String getParameter(String param) {
            String value = null;
            try {
                //post
                super.setCharacterEncoding(encoding);//把编码转换为encoding
                value = super.getParameter(param);
                if(super.getMethod().equalsIgnoreCase("GET")){
                    if(value!=null){
                        value = new String(value.getBytes("iso8859-1"),encoding);
                    }
                }
            } catch (UnsupportedEncodingException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return value;
        }

        public MyRequest(HttpServletRequest request) {
            super(request);
        }
        
    }
    protected String encoding=null; 
    public void destroy() { //销毁
        // TODO Auto-generated method stub
        this.encoding=null;
    }
   //对编码问题进行转换
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        response.setContentType("text/html;charset="+encoding);
        //过滤未登录用户
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse resp = (HttpServletResponse) response;
        String path=req.getServletPath();
        String param=req.getQueryString();
        if(path!=null){
            path=path+"?"+param;//全请求路径
        }
        if(path.endsWith("myAddress")||path.endsWith("myJingDong")||path.indexOf("myShouCang")!=-1||path.endsWith("updateUser")||path.indexOf("showOrder")!=-1||path.indexOf("showValidOrder")!=-1||path.indexOf("showCancelOrder")!=-1||path.indexOf("fillOrder")!=-1){
            HttpSession session = req.getSession();
            String userName = (String) session.getAttribute("username");
            if(userName == null){
                session.setAttribute("url", path.replaceFirst("/", ""));
                System.out.println(session.getAttribute("url"));
                resp.sendRedirect("user.do?op=loginAction");
                return;
            }
        }
        //把过滤器给下一个过滤器或资源处理器
        chain.doFilter(new MyRequest((HttpServletRequest) request), response); 
    }

    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        this.encoding=filterConfig.getInitParameter("encoding");//encoding在web.xml中指定
    }

}

然后在web.xml对该过滤器进行注册和映射：

<filter>
    <filter-name>EncodingFilter</filter-name>
    <filter-class>com.util.MyFilter</filter-class>
    <init-param>
       <param-name>encoding</param-name>
       <param-value>utf-8</param-value>
    </init-param>
  </filter>
 <filter-mapping>
     <filter-name>EncodingFilter</filter-name>
     <url-pattern>/*</url-pattern>
 </filter-mapping>

上面写的过滤器MyFilter类，本来只能处理post提交的数据(post是先处理后接收，get是先接收后处理)。

但是MyFilter里面在对任何页面过滤的时候，来了一个偷梁换柱：把原来客户端请求的request给换掉了，换成自己定义的一个request了，即内部类MyRequest，不过该类要继承一个类HttpServletRequestWrapper。

在自定义的一个内部类MyRequest里面，实现了一个好强大的功能，就是重写了request的getParameter()方法。该方法里面即处理了post提交，又能处理get提交，返回的值就是处理后的值，所以该过滤器就能实现处理post和get提交的乱码问题！