java10进制转换成16进制，4 字节，低位在前，高位在后

/**

 * 4字节
 * 低位在前，高位在后
 *
 * @param n
 * @return
 */
public static byte[] unlong2H4bytes(long n) {
    byte[] b = new byte[4];
    b[0] = (byte) (n & 0xff);
    b[1] = (byte) (n >> 8 & 0xff);
    b[2] = (byte) (n >> 16 & 0xff);
    b[3] = (byte) (n >> 24 & 0xff);
    return b;
}

/**
 * byte数组转为十六进制字符串
 *
 * @param bytes
 * @return
 */
public static String byte2Hex(byte[] bytes) {
    StringBuffer hexString = new StringBuffer();
    for (int i = 0; i < bytes.length; i++) {
        String hex = Integer.toHexString(0xff & bytes[i]);
        if (hex.length() == 1) {
            hexString.append('0');
        }
        hexString.append(hex);
    }
    return hexString.toString();
}

开始

int startTimeSecond = 1629359452;
byte[] bytes2 = unlong2H4bytes(startTimeSecond);
String s1 = byte2Hex(bytes2);
log.info("{}", s1);

结果
5c0d1e61