【Java基础】Java8中LocalDateTime，LocalDate，Long，Date，String 相互转换

    @Test
    public void testJava8DateFormat() {
        DateTimeFormatter dateTimeFormatter1 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        DateTimeFormatter dateTimeFormatter2 = DateTimeFormatter.ofPattern("yyyy-MM-dd");

        LocalDateTime localDateTime = LocalDateTime.parse("2019-07-31 00:00:00", dateTimeFormatter1);
        LocalDate localDate = LocalDate.parse("2019-07-31", dateTimeFormatter2);
        Date date = Date.from(LocalDateTime.parse("2019-07-31 00:00:00", dateTimeFormatter1).atZone(ZoneId.systemDefault()).toInstant());


        String strDateTime = "2019-07-31 00:00:00";
        String strDate = "2019-07-31";
        Long timestamp = 1564502400000L;

/** LocalDateTime 转 LocalDate */
        System.out.println("LocalDateTime 转 LocalDate: " + localDateTime.toLocalDate());
/** LocalDateTime 转 Long */
        System.out.println("LocalDateTime 转 Long: " + localDateTime.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli());
/** LocalDateTime 转 Date */
        System.out.println("LocalDateTime 转 Date: " + Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant()));
/** LocalDateTime 转 String */
        System.out.println("LocalDateTime 转 String: " + localDateTime.format(dateTimeFormatter1));

        System.out.println("-------------------------------");

/** LocalDate 转 LocalDateTime */
        System.out.println("LocalDate 转 LocalDateTime: " + LocalDateTime.of(localDate, LocalTime.parse("00:00:00")));
/** LocalDate 转 Long */
        System.out.println("LocalDate 转 Long: " + localDate.atStartOfDay(ZoneId.systemDefault()).toInstant().toEpochMilli());
/** LocalDate 转 Date */
        System.out.println("LocalDate 转 Date: " + Date.from(localDate.atStartOfDay().atZone(ZoneId.systemDefault()).toInstant()));
/** LocalDate 转 String */
        System.out.println("LocalDateTime 转 String: " + localDateTime.format(dateTimeFormatter2));

        System.out.println("-------------------------------");

/** Date 转 LocalDateTime */
        System.out.println("Date 转 LocalDateTime: " + LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault()));
/** Date 转 Long */
        System.out.println("Date 转 Long: " + date.getTime());
/** Date 转 LocalDate */
        System.out.println("Date 转 LocalDateTime: " + LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault()).toLocalDate());
/** Date 转 String */
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss SSS");
        System.out.println("Date 转 String: " + sdf.format(date));

        System.out.println("-------------------------------");

/** String 转 LocalDateTime */
        System.out.println("String 转 LocalDateTime: " + LocalDateTime.parse(strDateTime, dateTimeFormatter1));
/** String 转 LocalDate */
        System.out.println("String 转 LocalDate: " + LocalDateTime.parse(strDateTime, dateTimeFormatter1).toLocalDate());
        System.out.println("String 转 LocalDate: " + LocalDate.parse(strDate, dateTimeFormatter2));
/** String 转 Date */
        System.out.println("String 转 Date: " + Date.from(LocalDateTime.parse(strDateTime, dateTimeFormatter1).atZone(ZoneId.systemDefault()).toInstant()));

        System.out.println("-------------------------------");

/** Long 转 LocalDateTime */
        System.out.println("Long 转 LocalDateTime:" + LocalDateTime.ofInstant(Instant.ofEpochMilli(timestamp), ZoneId.systemDefault()));
/** Long 转 LocalDate */
        System.out.println("Long 转 LocalDate:" + LocalDateTime.ofInstant(Instant.ofEpochMilli(timestamp), ZoneId.systemDefault()).toLocalDate());
    }

执行结果：