java实现python bytes.fromhex()函数，将hex字符串转换为字节

    //Tribute to python
    public static byte[] bytesFromHex(String hexStr) {
        int len = hexStr.length()/2;
        byte[] result = new byte[len];
        for (int i = 0; i < len; i++) {
            result[i]=Byte.parseByte(hexStr.substring(i*2,i*2+2),16);
        }
        return result;
    }