public static String subPath(String rootDir, File file) {
		try {
			return subPath(rootDir, file.getCanonicalPath());
		} catch (IOException e) {
			throw new IORuntimeException(e);
		}
	}
@Test
	public void subPathTest2() {
		String subPath = FileUtil.subPath("d:/aaa/bbb/", "d:/aaa/bbb/ccc/");
		assertEquals("ccc/", subPath);

		subPath = FileUtil.subPath("d:/aaa/bbb", "d:/aaa/bbb/ccc/");
		assertEquals("ccc/", subPath);

		subPath = FileUtil.subPath("d:/aaa/bbb", "d:/aaa/bbb/ccc/test.txt");
		assertEquals("ccc/test.txt", subPath);

		subPath = FileUtil.subPath("d:/aaa/bbb/", "d:/aaa/bbb/ccc");
		assertEquals("ccc", subPath);

		subPath = FileUtil.subPath("d:/aaa/bbb", "d:/aaa/bbb/ccc");
		assertEquals("ccc", subPath);

		subPath = FileUtil.subPath("d:/aaa/bbb", "d:/aaa/bbb");
		assertEquals("", subPath);

		subPath = FileUtil.subPath("d:/aaa/bbb/", "d:/aaa/bbb");
		assertEquals("", subPath);
	}