/**

      * md5签名

      * @param plainText 要签名的字符串

      * @param enc 要编译的格式 gbk；utf-8

      * @return

      */

     public static String MD5(String plainText,String enc) {

         String re_md5 = new String();

         try {

             MessageDigest md = MessageDigest.getInstance("MD5");

             md.update(plainText.getBytes(enc));

             byte b[] = md.digest();

             int i;

             StringBuffer buf = new StringBuffer("");

             for (int offset = 0; offset < b.length; offset++) {

                 i = b[offset];

                 if (i < 0)

                     i += 256;

                 if (i < 16)

                     buf.append("0");

                 buf.append(Integer.toHexString(i));

             }

             re_md5 = buf.toString();

         } catch (Exception e) {

             e.printStackTrace();

         }

         return re_md5;

     }