public static File checkSlip(File parentFile, File file) throws IllegalArgumentException {
		if (null != parentFile && null != file) {
			if (false == isSub(parentFile, file)) {
				throw new IllegalArgumentException("New file is outside of the parent dir: " + file.getName());
			}
		}
		return file;
	}
@Test
	public void checkSlipTest() {
		assertThrows(IllegalArgumentException.class, ()->{
			FileUtil.checkSlip(FileUtil.file("test/a"), FileUtil.file("test/../a"));
		});
	}