java中md5加密

/**
   * 签名字符串
   * @param input_charset 编码格式
   * @return 签名结果
   */
  public static String sign(Map<String,String> map,String input_charset) {
   Map<String, String> map2 = new TreeMap<String, String>(
       new Comparator<String>() {
          @Override
           public int compare(String obj1, String obj2) {
               // 升序排序
               return obj1.compareTo(obj2);
           }
      });
   Set<String> keySet2 = map.keySet();
   for (String string : keySet2) {
      map2.put(string, map.get(string));
   }
   Set<String> keySet = map2.keySet();
   String text = "";
   int length = keySet.size();
   int i = 1;
      for (String string : keySet) {
   if(length == i){
      //if(!StringUtils.isEmpty(map.get(string))){
         text += string+"="+map.get(string);
      //}
   }else{
      //if(!StringUtils.isEmpty(map.get(string))){
         text += string+"="+map.get(string)+",";
      //}
   }
   i++;
}
      log.info("签名参数={}",text);
      return DigestUtils.md5Hex(getContentBytes(text, input_charset));
  }
  
  /**
   * @param content
   * @param charset
   * @return
   * @throws SignatureException
   * @throws UnsupportedEncodingException 
   */
  private static byte[] getContentBytes(String content, String charset) {
      if (charset == null || "".equals(charset)) {
          return content.getBytes();
      }
      try {
          return content.getBytes(charset);
      } catch (UnsupportedEncodingException e) {
          throw new RuntimeException("MD5签名过程中出现错误,指定的编码集不对,您目前指定的编码集是:" + charset);
      }
  }