我们不太可能使用jdk8以后就把原来的代码都改成新api。所以新旧日期类会共存一段时间。

这篇提供他们之间的转换。

    public static void main(String[] args) {
        //Date 转 Instant
        Instant timestamp = new Date().toInstant();
        //其他类都有ofInstant方法用来转换Instant
        LocalDateTime date = LocalDateTime.ofInstant(timestamp, ZoneId.of(ZoneId.SHORT_IDS.get("CTT")));
        System.out.println(date);

        //Calendar 转 Instant
        Instant time = Calendar.getInstance().toInstant();
        System.out.println(time);
        //TimeZone 转 ZoneId
        ZoneId defaultZone = TimeZone.getDefault().toZoneId();
        System.out.println(defaultZone);

        //Calendar 转 ZonedDateTime
        ZonedDateTime gregorianCalendarDateTime = new GregorianCalendar().toZonedDateTime();
        System.out.println(gregorianCalendarDateTime);

        //兼容API
        Date dt = Date.from(Instant.now());
        System.out.println(dt);

        TimeZone tz = TimeZone.getTimeZone(defaultZone);
        System.out.println(tz);

        GregorianCalendar gc = GregorianCalendar.from(gregorianCalendarDateTime);
        System.out.println(gc);
    }