public static String extName(File file) {
		return FileNameUtil.extName(file);
	}
@Test
	public void extNameTest() {
		String path =  FileUtil.isWindows() ? "d:\\aaa\\bbb\\cc\\ddd\\" : "~/Desktop/hutool/ddd/";
		String mainName = FileUtil.extName(path);
		assertEquals("", mainName);

		path =  FileUtil.isWindows() ? "d:\\aaa\\bbb\\cc\\ddd" : "~/Desktop/hutool/ddd";
		mainName = FileUtil.extName(path);
		assertEquals("", mainName);

		path = FileUtil.isWindows() ? "d:\\aaa\\bbb\\cc\\ddd.jpg" : "~/Desktop/hutool/ddd.jpg";
		mainName = FileUtil.extName(path);
		assertEquals("jpg", mainName);

		path = FileUtil.isWindows() ? "d:\\aaa\\bbb\\cc\\fff.xlsx" : "~/Desktop/hutool/fff.xlsx";
		mainName = FileUtil.extName(path);
		assertEquals("xlsx", mainName);

		path = FileUtil.isWindows() ? "d:\\aaa\\bbb\\cc\\fff.tar.gz" : "~/Desktop/hutool/fff.tar.gz";
		mainName = FileUtil.extName(path);
		assertEquals("tar.gz", mainName);

		path = FileUtil.isWindows() ? "d:\\aaa\\bbb\\cc\\fff.tar.Z" : "~/Desktop/hutool/fff.tar.Z";
		mainName = FileUtil.extName(path);
		assertEquals("tar.Z", mainName);

		path = FileUtil.isWindows() ? "d:\\aaa\\bbb\\cc\\fff.tar.bz2" : "~/Desktop/hutool/fff.tar.bz2";
		mainName = FileUtil.extName(path);
		assertEquals("tar.bz2", mainName);

		path = FileUtil.isWindows() ? "d:\\aaa\\bbb\\cc\\fff.tar.xz" : "~/Desktop/hutool/fff.tar.xz";
		mainName = FileUtil.extName(path);
		assertEquals("tar.xz", mainName);
	}