时间类

/**
 * 日期：2019/7/24.
 * 功能：
 *      1. 时间戳 -> Instant -> LocalDateTime -> Instant -> 时间戳
 *      2. 格式化：LocalDateTime -> 字符串
 *         解  析：字符串 -> LocalDateTime
 */
public class MyDemo {

    @Test
    public void TimeStampAndDateTime() {
        System.out.println("System  获取的时间戳：" + System.currentTimeMillis());
        System.out.println("Instant 获取的时间戳：" + Instant.now().getEpochSecond() + "\n");
        Long systemTimeMillis = System.currentTimeMillis();

        //long型时间戳转 Instant
        Instant instant = Instant.ofEpochMilli(systemTimeMillis);
        System.out.println("long型时间戳转 Instant：   " + systemTimeMillis + " --> " + instant + "\n");

        //Instant 转 LocalDateTime
        LocalDateTime ldt = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());
        System.out.println("Instant 转 LocalDateTime：" + instant + " --> " + ldt + "\n");

        //LocalDateTime 转 Instant
        Instant instant2 = ldt.toInstant(ZoneOffset.of("+8"));
        System.out.println("LocalDateTime 转 Instant：" + ldt + " --> " + instant2 + "\n");

        //Instant 转 long型时间戳
        long systemTimeMillis2 = instant2.toEpochMilli();
        System.out.println("Instant 转 long型时间戳：" + instant2 + " --> " + systemTimeMillis2);
    }


    @Test
    public void formatAndParse() {
        LocalDateTime ldt = LocalDateTime.now();

        //将LocalDateTime格式化成特定格式的字符串
        DateTimeFormatter dtf2 = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH:mm:ss");
        String newDateString = dtf2.format(ldt);
        System.out.println("LocalDateTime --> 字符串 : " + ldt + " --> " + newDateString);

        //将字符串解析成 LocalDateTime
        LocalDateTime ldt2 = LocalDateTime.parse(newDateString, dtf2);
        System.out.println("字符串 --> LocalDateTime : " + newDateString + " --> " + ldt2);
    }
}