过滤器过滤乱码

package com.xy.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;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.t59.model.dto.Userinfo;

/**
 * 文本过滤器过滤乱码
 *
 * @author 小月
 *
 */
public class CodeFilter extends HttpServlet implements Filter {
 private FilterConfig filterConfig;

 public void init(FilterConfig filterConfig) throws ServletException {
  this.filterConfig = filterConfig;
 }

 public void doFilter(ServletRequest request, ServletResponse response,
   FilterChain filterChain) {
  try {
   ((HttpServletResponse) response).setHeader("Cache-Control",
     "no-cache");
   ((HttpServletResponse) response).setHeader("Pragma", "no-cache");
   ((HttpServletResponse) response).setDateHeader("Expires", -1);
   request.setCharacterEncoding("gb2312");
   response.setCharacterEncoding("gb2312");
   filterChain.doFilter(request, response);

  } catch (ServletException sx) {
   filterConfig.getServletContext().log(sx.getMessage());
  } catch (IOException iox) {
   filterConfig.getServletContext().log(iox.getMessage());
  }
 }

 public void destroy() {
 }
}