public class PackUtil{

/**
 * 打包字符串
 * 类似php中pack在java中的实现
 *
 * @param str
 * @return
 */
public static byte[] pack(String str) {
  int nibbleshift = 4;
  int position = 0;
  int len = str.length() / 2 + str.length() % 2;
  byte[] output = new byte[len];
  for (char v : str.toCharArray()) {
    byte n = (byte) v;
    if (n >= '0' && n <= '9') {
      n -= '0';
    } else if (n >= 'A' && n <= 'F') {
      n -= ('A' - 10);
    } else if (n >= 'a' && n <= 'f') {
      n -= ('a' - 10);
    } else {
      continue;
    }
    output[position] |= (n << nibbleshift);

    if (nibbleshift == 0) {
      position++;
    }
    nibbleshift = (nibbleshift + 4) & 7;
  }

  return output;
}

/**
 * 16进制的字符解压 类<a href="https://www.jb51.cc/tag/PHP/" target="_blank" class="keywords">PHP</a>中unpack
 *
 * @param is
 * @param len
 * @return
 * @throws IOException
 */
public static String unpack(InputStream is,int len) throws IOException {
  byte[] bytes = new byte[len];
  is.read(bytes);
  return unpack(bytes);
}

/***
 * 16进制的字符解压 类<a href="https://www.jb51.cc/tag/PHP/" target="_blank" class="keywords">PHP</a>中unpack
 * @param bytes
 * @return
 */
public static String unpack(byte[] bytes) {
  StringBuilder stringBuilder = new StringBuilder("");
  if (bytes == null || bytes.length <= 0) {
    return null;
  }
  for (int i = 0; i < bytes.length; i++) {
    int v = bytes[i] & 0xFF;
    String hv = Integer.toHexString(v);
    if (hv.length() < 2) {
      stringBuilder.append(0);
    }
    stringBuilder.append(hv);
  }
  return stringBuilder.toString();
}

}