apollo-core/src/main/java/com/ctrip/framework/apollo/core/utils/ByteUtil.java/ByteUtil/toHexString
class ByteUtil:  public static String toHexString(byte[] bytes) {
    char[] chars = new char[bytes.length * 2];
    int i = 0;
    for (byte b : bytes) {
      chars[i++] = HEX_CHARS[b >> 4 & 0xF];
      chars[i++] = HEX_CHARS[b & 0xF];
    }
    return new String(chars);
  }