Java simulates PHP's pack and unpack classes_php tips

package qghl.intp.util;
 
import java.io.IOException;
import java.io.InputStream;
 
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php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php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();
    }
  }