java中String byte HexString的转换

 public static byte[] hexStringToBytes(String hexString) {
        if (hexString == null || hexString.equals("")) {
            return null;
        }
        hexString = hexString.toUpperCase();
        int length = hexString.length() / 2;
        char[] hexChars = hexString.toCharArray();
        byte[] d = new byte[length];
        for (int i = 0; i < length; i++) {
            int pos = i * 2;
            d[i] = (byte) (charToByte(hexChars[pos]) << 4 | charToByte(hexChars[pos + 1])); 
        }
        return d;
    }
    private static byte charToByte(char c) {
        return (byte) "0123456789ABCDEF".indexOf(c);
    }

 public static String bytesToHexString(byte[] src){
        StringBuilder stringBuilder = new StringBuilder("");
        if (src == null || src.length <= 0) {
            return null;
        }
        for (int i = 0; i < src.length; i++) {
            int v = src[i] & 0xFF;
            String hv = Integer.toHexString(v);
            if (hv.length() < 2) {
                stringBuilder.append(0);
            }
            stringBuilder.append(hv);
        }
        return stringBuilder.toString();
    }

public   String printHexString( byte[] b) {
String a = "";
  for (int i = 0; i < b.length; i++) { 
    String hex = Integer.toHexString(b[i] & 0xFF); 
    if (hex.length() == 1) { 
      hex = ‘0‘ + hex; 
    }
   
    a = a+hex;
  } 
       return a;
}