Java日期时间字符串和毫秒相互转换的方法

@Test
public void test() throws ParseException {
  String dateTime = "2016-12-31 12:30:45 123";
  Calendar calendar = Calendar.getInstance();
  calendar.setTime(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss SSS").parse(dateTime));
  System.out.println("日期[2016-12-31 12:30:45 123]对应毫秒：" + calendar.getTimeInMillis());
}

@Test
public void test() {
  long millisecond = 1483159625851l;
  Date date = new Date(millisecond);
  SimpleDateFormat format = new SimpleDateFormat("yyyy年MM月dd日 hh:mm:ss SSS a");
  System.out.println("毫秒[1483159625851]对应日期时间字符串：" + format.format(date));
}