public static boolean checkFileExist(String file) {
        return FILES.contains(file);
    }
@Test
    public void testAfterHttpDataReleaseCheckFileExist() throws IOException {

        String filePath = fu.getFile().getPath();
        assertTrue(DeleteFileOnExitHook.checkFileExist(filePath));

        fu.release();
        assertFalse(DeleteFileOnExitHook.checkFileExist(filePath));
    }