Java日期时间API系列31—–Jdk8中java.time包中的新的日期时间API类,时间戳的获取方式对比、转换和使用。

 

  时间戳是指格林威治时间1970年01月01日00时00分00秒起至现在的总毫秒数,是所有时间的基础,其他时间可以通过时间戳转换得到。Java中本来已经有相关获取时间戳的方法,Java8后增加新的类Instant等专用于处理时间戳问题。

 

 1 获取时间戳的方法和性能对比

1.1 获取时间戳方法

Java8以前可以使用System.currentTimeMillis() 、new Date().getTime() 、和Calendar.getInstance().getTimeInMillis()获取。Java8以后可以另外通过Instant.now().toEpochMilli()和Clock.systemUTC().millis()获取。

比较简单,下面直接看代码:

    /**
     * 使用System获取时间戳
     */
    @Test
    public void getEpochMilliWithSystem(){
        long s = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            System.currentTimeMillis();
        }
        System.out.println("getEpochMilliWithSystem cost:"+(System.currentTimeMillis()-s));
    }
    
    /**
     * 使用Date获取时间戳
     */
    @Test
    public void getEpochMilliWithDate(){
        long s = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            new Date().getTime();
        }
        System.out.println("getEpochMilliWithDate cost:"+(System.currentTimeMillis()-s));
    }
    
    /**
     * 使用Calendar获取时间戳
     */
    @Test
    public void getEpochMilliWithCalendar(){
        long s = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            Calendar.getInstance().getTimeInMillis();
        }
        System.out.println("getEpochMilliWithCalendar cost:"+(System.currentTimeMillis()-s));
    }
    
    /**
     * 使用Instant获取时间戳
     */
    @Test
    public void getEpochMilliWithInstant(){
        long s = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            Instant.now().toEpochMilli();
        }
        System.out.println("getEpochMilliWithInstant cost:"+(System.currentTimeMillis()-s));
    }
    
    /**
     * 使用Clock获取时间戳
     */
    @Test
    public void getEpochMilliWithClock(){
        long s = System.currentTimeMillis();
        for (int i = 0; i < 1000000; i++) {
            Clock.systemUTC().millis();
        }
        System.out.println("getEpochMilliWithClock cost:"+(System.currentTimeMillis()-s));
    }

查看过上面相关源码,基本都是通过System.currentTimeMillis() 来创建对象的。比如 new Date:

    public Date() {
        this(System.currentTimeMillis());
    }

 

1.2 性能对比

上面代码执行输出:

getEpochMilliWithSystem cost:5
getEpochMilliWithDate cost:38
getEpochMilliWithCalendar cost:1094
getEpochMilliWithInstant cost:106
getEpochMilliWithClock cost:17

通过1.1 中的分析得知基本都是通过System.currentTimeMillis() 来创建对象的System.currentTimeMillis()最快,性能最好。

所以,性能排序:System > Clock > DateInstant > Calendar

 

2.时间戳转换为其他类

 2.1 时间戳和其他类型的转换

    /**
     * 时间戳epochMilli毫秒转Date
     * @param epochMilli
     * @return
     */
    public static Date toDate(long epochMilli){
        Objects.requireNonNull(epochMilli, "epochMilli");
        return new Date(epochMilli);
    }
    /**
     * 时间戳epochMilli毫秒转LocalDateTime
     * @param epochMilli
     * @return
     */
    public static LocalDateTime toLocalDateTime(long epochMilli) {
        Objects.requireNonNull(epochMilli, "epochMilli");
        return LocalDateTime.ofInstant(Instant.ofEpochMilli(epochMilli), ZoneId.systemDefault());
    }
    /**
     * 时间戳epochMilli毫秒转LocalDate
     * @param epochMilli
     * @return
     */
    public static LocalDate toLocalDate(long epochMilli) {
        Objects.requireNonNull(epochMilli, "epochMilli");
        return toLocalDateTime(epochMilli).toLocalDate();
    }
    /**
     * 时间戳epochMilli毫秒转Instant
     * @param epochMilli
     * @return
     */
    public static Instant toInstant(long epochMilli) {
        Objects.requireNonNull(epochMilli, "epochMilli");
        return Instant.ofEpochMilli(epochMilli);
    }
    /**
     * 时间戳epochMilli毫秒转ZonedDateTime,时区为系统默认时区
     * @param epochMilli
     * @return
     */
    public static ZonedDateTime toZonedDateTime(long epochMilli) {
        Objects.requireNonNull(epochMilli, "epochMilli");
        return LocalDateTime.ofInstant(Instant.ofEpochMilli(epochMilli), ZoneId.systemDefault())
                .atZone(ZoneId.systemDefault());
    }
    /**
     * 时间戳epochMilli转Timestamp
     * @param epochMilli
     * @return
     */
    public static Timestamp toTimestamp(long epochMilli){
        return new Timestamp(epochMilli);
    }

    /**
     * Date转时间戳
     * 从1970-01-01T00:00:00Z开始的毫秒值
     * @param date
     * @return
     */
    public static long toEpochMilli(Date date){
        Objects.requireNonNull(date, "date");
        return date.getTime();
    }
    /**
     * LocalDateTime转时间戳
     * 从1970-01-01T00:00:00Z开始的毫秒值
     * @param localDateTime
     * @return
     */
    public static long toEpochMilli(LocalDateTime localDateTime){
        return toInstant(localDateTime).toEpochMilli();
    }
    /**
     * LocalDate转时间戳
     * 从1970-01-01T00:00:00Z开始的毫秒值
     * @param localDate
     * @return
     */
    public static long toEpochMilli(LocalDate localDate){
        return toInstant(localDate).toEpochMilli();
    }
    /**
     * Instant转时间戳
     * 从1970-01-01T00:00:00Z开始的毫秒值
     * @param instant
     * @return
     */
    public static long toEpochMilli(Instant instant){
        Objects.requireNonNull(instant, "instant");
        return instant.toEpochMilli();
    }
    /**
     * ZonedDateTime转时间戳,注意,zonedDateTime时区必须和当前系统时区一致,不然会出现问题
     * 从1970-01-01T00:00:00Z开始的毫秒值
     * @param zonedDateTime
     * @return
     */
    public static long toEpochMilli(ZonedDateTime zonedDateTime) {
        Objects.requireNonNull(zonedDateTime, "zonedDateTime");
        return zonedDateTime.toInstant().toEpochMilli();
    }
    /**
     * Timestamp转时间戳
     * 从1970-01-01T00:00:00Z开始的毫秒值
     * @param timestamp
     * @return
     */
    public static long toEpochMilli(Timestamp timestamp){
        Objects.requireNonNull(timestamp, "timestamp");
        return timestamp.getTime();
    }

 

测试代码:

    /**
     * 时间戳转换测试
     */
    @Test
    public void epochMilliConverterTest(){
        System.out.println("===================epochMilliConverterTest=====================");
        Date date = new Date();
        long epochMilli = date.getTime();
        System.out.println("epochMilli:"+epochMilli);
        System.out.println("===================ToOther=====================");
        System.out.println(DateTimeConverterUtil.toDate(epochMilli));
        System.out.println(DateTimeConverterUtil.toLocalDateTime(epochMilli));
        System.out.println(DateTimeConverterUtil.toLocalDate(epochMilli));
        System.out.println(DateTimeConverterUtil.toInstant(epochMilli));
        System.out.println(DateTimeConverterUtil.toZonedDateTime(epochMilli));
        System.out.println(DateTimeConverterUtil.toTimestamp(epochMilli));
        System.out.println("===================toEpochMilli=====================");
        System.out.println(DateTimeConverterUtil.toEpochMilli(new Date()));
        System.out.println(DateTimeConverterUtil.toEpochMilli(LocalDateTime.now()));
        // 另一种方式: +8 时区
        System.out.println(LocalDateTime.now().toInstant(ZoneOffset.of("+8")).toEpochMilli());
        System.out.println(DateTimeConverterUtil.toEpochMilli(LocalDate.now()));
        System.out.println(DateTimeConverterUtil.toEpochMilli(Instant.now()));
        System.out.println(DateTimeConverterUtil.toEpochMilli(ZonedDateTime.now()));
        System.out.println(DateTimeConverterUtil.toEpochMilli(new Timestamp(System.currentTimeMillis())));
    }

 

输出:

===================epochMilliConverterTest=====================
epochMilli:1587950768191
===================ToOther=====================
Mon Apr 27 09:26:08 CST 2020
2020-04-27T09:26:08.191
2020-04-27
2020-04-27T01:26:08.191Z
2020-04-27T09:26:08.191+08:00[Asia/Shanghai]
2020-04-27 09:26:08.191
===================toEpochMilli=====================
1587950768304
1587950768304
1587950768304
1587916800000
1587950768305
1587950768305
1587950768305

 

 3 Timestamp

Timestamp是Java8以前处理时间戳的类。Timestamp和其他类型的转换

    /**
     * Timestamp转LocalDateTime
     * @param timestamp
     * @return
     */
    public static LocalDateTime toLocalDateTime(Timestamp timestamp) {
        Objects.requireNonNull(timestamp, "timestamp");
        return timestamp.toLocalDateTime();
    }
    /**
     * Timestamp转Instant
     * @param timestamp
     * @return
     */
    public static Instant toInstant(Timestamp timestamp) {
        Objects.requireNonNull(timestamp, "timestamp");
        return timestamp.toInstant();
    }
    /**
     * Timestamp转时间戳
     * 从1970-01-01T00:00:00Z开始的毫秒值
     * @param timestamp
     * @return
     */
    public static long toEpochMilli(Timestamp timestamp){
        Objects.requireNonNull(timestamp, "timestamp");
        return timestamp.getTime();
    }
    /**
     * Date转Timestamp
     * @param date
     * @return
     */
    public static Timestamp toTimestamp(Date date){
        Objects.requireNonNull(date, "date");
        return new Timestamp(date.getTime());
    }
    /**
     * LocalDateTime转Timestamp
     * @param localDateTime
     * @return
     */
    public static Timestamp toTimestamp(LocalDateTime localDateTime){
        Objects.requireNonNull(localDateTime, "localDateTime");
        return Timestamp.valueOf(localDateTime);
    }
    
    /**
     * Instant转Timestamp
     * @param instant
     * @return
     */
    public static Timestamp toTimestamp(Instant instant){
        Objects.requireNonNull(instant, "instant");
        return Timestamp.from(instant);
    }

    /**
     * 时间戳epochMilli转Timestamp
     * @param epochMilli
     * @return
     */
    public static Timestamp toTimestamp(long epochMilli){
        return new Timestamp(epochMilli);
    }

测试代码:

    /**
     * Timestamp转换测试
     */
    @Test
    public void timestampConverterTest(){
        System.out.println("===================timestampConverterTest=====================");
        Timestamp timestamp = new Timestamp(System.currentTimeMillis());
        long epochMilli = timestamp.getTime();
        System.out.println("epochMilli:"+epochMilli);
        System.out.println("===================ToOther=====================");
        System.out.println(DateTimeConverterUtil.toLocalDateTime(timestamp));
        System.out.println(DateTimeConverterUtil.toInstant(timestamp));
        System.out.println(DateTimeConverterUtil.toEpochMilli(timestamp));
        System.out.println("===================toEpochMilli=====================");
        System.out.println(DateTimeConverterUtil.toTimestamp(new Date()));
        System.out.println(DateTimeConverterUtil.toTimestamp(LocalDateTime.now()));
        System.out.println(DateTimeConverterUtil.toTimestamp(Instant.now()));
        System.out.println(DateTimeConverterUtil.toTimestamp(epochMilli));
    }

输出:

===================timestampConverterTest=====================
epochMilli:1587950937677
===================ToOther=====================
2020-04-27T09:28:57.677
2020-04-27T01:28:57.677Z
1587950937677
===================toEpochMilli=====================
2020-04-27 09:28:57.774
2020-04-27 09:28:57.781
2020-04-27 09:28:57.782
2020-04-27 09:28:57.677

 

4 Instant

Java8可以使用Instant方便的获取时间戳相关的信息。

4.1 创建方式

    public static Instant now() {
        return Clock.systemUTC().instant();
    }

Instant now方法默认使用的是UTC,协调世界时。now(Clock clock)方法
clock参数可以设置时区信息,就可以获取不同时区的Instant,比如 Clock systemDefaultZone()
或指定时区 Clock system(ZoneId zone)等。



4.2 获取时间戳


public long toEpochMilli() 获取时间戳 单位为毫秒。

public long getEpochSecond() 获取时间戳 单位为秒。

 

5.总结

   通过上面可以看出,时间戳是所有时间创建和转换的基础,通过简单的System.currentTimeMillis()获取到,但时间戳只是一个简单的数字,不转换为其他时间类没有意义,比如 年、月、日、时、分、秒、星期、闰年、时区、夏令时等,更多相关的比如各种节假日,星座等附加意义的信息。

 

源代码地址:https://github.com/xkzhangsan/xk-time