ava字符串长度截取 考虑汉字

 public static String getLimitLengthString( String str,int len){
      try{
      int counterOfDoubleByte = 0;
      byte[] b = str.getBytes("gb2312");
      if(b.length <= len)
      return str;
      for(int i = 0; i < len; i++){
      if(b[i] < 0)
      counterOfDoubleByte++;
      }
      if(counterOfDoubleByte % 2 == 0)
      return new String(b, 0, len, "gb2312");
      else
      return new String(b, 0, len - 1, "gb2312");
      }catch(Exception ex){
      DBTools.error(ex);
      return "";
      }
      }