public static String gmtDate() {
        return GMT_FMT.format(LocalDateTime.now().atZone(GMT_ZONE_ID));
    }
@Test
    public void testGmtDate() {
        String gmt = DateKit.gmtDate(date);
        Assert.assertEquals("Wed, 20 Sep 2017 15:27:50 GMT", gmt);

        gmt = DateKit.gmtDate(localDateTime);
        Assert.assertEquals("Wed, 20 Sep 2017 15:20:10 GMT", gmt);

        Assert.assertNotNull(DateKit.gmtDate());
    }