code: public static char[] binToHex(byte[] bytes, int offset, int len) {
          final char[] sb = new char[len * 2];
          final int end = offset + len;
          int index = 0;
          final char[] hexs = hex;
          for (int i = offset; i < end; i++) {
              byte b = bytes[i];
              sb[index++] = (hexs[((b >> 4) & 0xF)]);
              sb[index++] = hexs[((b) & 0xF)];
          }
          return sb;
      }
docs: 将字节数组转换为16进制字符数组
  
  @param bytes  字节数组
  @param offset 偏移量
  @param len    长度
  
  @return 16进制字符串的字符数组