Java中Date类的使用

川长思鸟来 2023-02-20 02:59 123阅读 0赞

**目录**

一、获取当前时间

二、获取昨天的时间

三、Date与Date之间的比较

四、获取Date的部分信息（年、月、日）

五、Date和String的相互转换

六、Date和Calendar的相互转换

七、Date和时间戳（long）的相互转换

八、Date和时间戳（java.sql.Timestamp）的相互转换

--------------------

### 一、获取当前时间 ###

// 1、获取当前日期直接输出
            Date today1 = new Date();
            System.out.println(today1+"   "+today1.toString());
            //Mon Jun 22 20:17:29 CST 2020   Mon Jun 22 20:17:29 CST 2020
    
            LocalDate today2 = LocalDate.now(); //Java 8
            System.out.println(today2+" "+today2.toString());
            //2020-06-22 2020-06-22

获取当前时间戳（毫秒级）的三种方式：

//获取当前时间戳
            System.out.println(System.currentTimeMillis());
            System.out.println(Calendar.getInstance().getTimeInMillis());
            System.out.println(new Date().getTime());
            //1592913592149
            //1592913592150
            //1592913592151

### 二、获取昨天的时间 ###

// 2、获取昨天日期
            Date yesterday1 = new Date(new Date().getTime() - 24 * 60 * 60 * 1000);
            System.out.println(yesterday1+"  "+yesterday1.toString());
            //Sun Jun 21 20:17:29 CST 2020  Sun Jun 21 20:17:29 CST 2020
    
            //错误的用法：如果今天是6月1号，则得到的昨天日期是5月30号
            Calendar calendar = Calendar.getInstance();
            System.out.println(calendar.toString());
            //java.util.GregorianCalendar[time=1592828249605,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=29,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2020,MONTH=5,WEEK_OF_YEAR=26,WEEK_OF_MONTH=4,DAY_OF_MONTH=22,DAY_OF_YEAR=174,DAY_OF_WEEK=2,DAY_OF_WEEK_IN_MONTH=4,AM_PM=1,HOUR=8,HOUR_OF_DAY=20,MINUTE=17,SECOND=29,MILLISECOND=605,ZONE_OFFSET=28800000,DST_OFFSET=0]
            calendar.add(Calendar.DATE, -1);    //calendar.set(Calendar.DATE, -1);  //使用calendar.add(Calendar.DAY_OF_MONTH, -1);估计就对了
            System.out.println(calendar.toString());
            //java.util.GregorianCalendar[time=1592741849605,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=29,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2020,MONTH=5,WEEK_OF_YEAR=26,WEEK_OF_MONTH=4,DAY_OF_MONTH=21,DAY_OF_YEAR=173,DAY_OF_WEEK=1,DAY_OF_WEEK_IN_MONTH=3,AM_PM=1,HOUR=8,HOUR_OF_DAY=20,MINUTE=17,SECOND=29,MILLISECOND=605,ZONE_OFFSET=28800000,DST_OFFSET=0]
            Date yesterday2 = calendar.getTime();
            System.out.println(yesterday2 +" "+ yesterday2.toString());
            //Sun Jun 21 20:17:29 CST 2020  Sun Jun 21 20:17:29 CST 2020
            //正确的用法
            Calendar calendar1 = Calendar.getInstance();
            calendar1.set(Calendar.HOUR_OF_DAY, -24);   //Calendar.HOUR_OF_DAY是24小时制，Calendar.HOUR是12小时制
            yesterday2 = calendar1.getTime();
            System.out.println(yesterday2 +" "+ yesterday2.toString());
            //Sun Jun 21 20:17:29 CST 2020  Sun Jun 21 20:17:29 CST 2020
    
            //使用Apache Commons Lang工具包的org.apache.commons.lang3.time.DateUtils工具类
            Date yesterday3 = DateUtils.addDays(new Date(), -1);
            System.out.println(yesterday3+" "+yesterday3.toString());
            //Sun Jun 21 20:17:29 CST 2020  Sun Jun 21 20:17:29 CST 2020

使用[Apache Commons Lang][]工具包需要在pom.xml文件引入依赖：

<dependency>
                <groupId>org.apache.commons</groupId>
                <artifactId>commons-lang3</artifactId>
                <version>3.3.2</version>
            </dependency>

### 三、Date与Date之间的比较 ###

// 3、Date与Date之间的比较
            Date date1 = new Date();
            Date date2 = new Date();
            Date date3 = DateUtils.addDays(new Date(), 1);
            int compare12 = date1.compareTo(date2);
            int compare13 = date1.compareTo(date3);
            System.out.println(compare12 +" "+ compare13);
            //0 -1

如果是LocalDate类之间的比较

LocalDate today = LocalDate.now();  //Java 8
            LocalDate oneDay = LocalDate.of(2019, 9, 9);
            System.out.println(today+"  "+oneDay+"  "+oneDay.equals(today));
            //2020-06-22  2019-09-09  false

### 四、获取Date的部分信息（年、月、日） ###

// 4、获取Date的年、月、日
            Date date = new Date();
            int dateDate = date.getDate();
            int dateYear = date.getYear();
            int dateMonth = date.getMonth();
            int dateDay = date.getDay();
            int dateHour = date.getHours();
            int dateMinute = date.getMinutes();
            int dateSecond = date.getSeconds();
            System.out.println(dateDate+"        "+dateYear+"/"+dateMonth+"/"+dateDay +"        "+ dateHour+"/"+dateMinute+"/"+dateSecond);
            //22        120/5/1        20/40/25

Date获取年月日的方法实际上已经废弃了，最好还是使用以下方式

Calendar calendar2 = new GregorianCalendar();
            int year = calendar2.get(Calendar.YEAR);    //2020
            int month = calendar2.get(Calendar.MONTH);    //5
            int dayOfYear = calendar2.get(Calendar.DAY_OF_YEAR);    //174
            int dayOfMonth = calendar2.get(Calendar.DAY_OF_MONTH);    //22
            int dayOfWeek = calendar2.get(Calendar.DAY_OF_WEEK);    //2
            int weekOfMonth = calendar2.get(Calendar.WEEK_OF_MONTH);    //4
            int weekOfYear = calendar2.get(Calendar.WEEK_OF_YEAR);    //26
            //
            int hour = calendar2.get(Calendar.HOUR);    //8
            int hourOfDay = calendar2.get(Calendar.HOUR_OF_DAY);    //20
            int minute = calendar2.get(Calendar.MINUTE);    //47
            int second = calendar2.get(Calendar.SECOND);    //34
            int millisecond = calendar2.get(Calendar.MILLISECOND);    //745

如果是LocalDate类的话

LocalDate localDate = LocalDate.now();  //Java 8
            int year2 = localDate.getYear();    //2020
            int month2 = localDate.getMonthValue();    //6
            Month month3 = localDate.getMonth();    //"JUNE"
            int day2 = localDate.getDayOfMonth();    //22
            DayOfWeek day3 = localDate.getDayOfWeek();    //"MONDAY"
            int day4 = localDate.getDayOfYear();    //174

### 五、Date和String的相互转换 ###

// 1、将Date转换成String
            // SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");      //2020-06-22 17:41:25
            // SimpleDateFormat sdf = new SimpleDateFormat("dd/M/yyyy");           //22/6/2020
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH时mm分ss秒");
            Date date = new Date();
            String today = sdf.format(date);
            System.out.println(today);
            //2020年06月22日 21时00分45秒
    
            // 2、将String转换成Date
            String  dateInString = today;
            Date newDate = null;
            try {
                newDate = sdf.parse(dateInString);
            } catch (ParseException e) {
    
            }
            System.out.println(newDate);
            //Mon Jun 22 21:00:45 CST 2020

SimpleDateFormat的常用表示为：

y: year
    M: month
    d: day in month
    D: day in year
    F: day of week in month (2)
    E: day in week (Tuesday)
    H: 0 - 23
    h: 1 - 12
    k: 1 - 24
    K: 0 - 11
    m: 分
    s: 秒
    S: 毫秒

### 六、Date和Calendar的相互转换 ###

//1、将Date转换成Calendar
            Date date = new Date();
            Calendar calendar = Calendar.getInstance();
            System.out.println(calendar.toString());
            //java.util.GregorianCalendar[time=1592831432364,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=29,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2020,MONTH=5,WEEK_OF_YEAR=26,WEEK_OF_MONTH=4,DAY_OF_MONTH=22,DAY_OF_YEAR=174,DAY_OF_WEEK=2,DAY_OF_WEEK_IN_MONTH=4,AM_PM=1,HOUR=9,HOUR_OF_DAY=21,MINUTE=10,SECOND=32,MILLISECOND=364,ZONE_OFFSET=28800000,DST_OFFSET=0]
            calendar.setTime(date);
            System.out.println(calendar.toString());
            //java.util.GregorianCalendar[time=1592831432357,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="Asia/Shanghai",offset=28800000,dstSavings=0,useDaylight=false,transitions=29,lastRule=null],firstDayOfWeek=1,minimalDaysInFirstWeek=1,ERA=1,YEAR=2020,MONTH=5,WEEK_OF_YEAR=26,WEEK_OF_MONTH=4,DAY_OF_MONTH=22,DAY_OF_YEAR=174,DAY_OF_WEEK=2,DAY_OF_WEEK_IN_MONTH=4,AM_PM=1,HOUR=9,HOUR_OF_DAY=21,MINUTE=10,SECOND=32,MILLISECOND=357,ZONE_OFFSET=28800000,DST_OFFSET=0]
    
            //2、将Calendar转换成Date
            Date date2 = calendar.getTime();
            System.out.println(date+"   "+date2+"   "+date.equals(date2));
            //Mon Jun 22 21:10:32 CST 2020   Mon Jun 22 21:10:32 CST 2020   true

### 七、Date和时间戳（long）的相互转换 ###

// 1、将Date转换成时间戳(long)
            Date today = new Date();
            System.out.println(today.getTime());
            //1592831024568
    
            // 2、将时间戳（long）转换成Date
            long timestamp = today.getTime();
            Date newDate = new Date(timestamp);
            System.out.println(newDate);
            //Mon Jun 22 21:03:44 CST 2020

String和时间戳（long）之间的转换需要借助Date和时间戳（long）之间的转换，如下所示就是将String转换成时间戳（long）

// 3、将String转换成时间戳
            String date = "2016-6-6 00:00:00";
            // 先将String转换成Date
            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            Date date1 = null;
            try {
                date1 = simpleDateFormat.parse(date);
            } catch (ParseException e) {
    
            }
            // 再将Date转换成时间戳（long）
            long timestamp1 = date1.getTime() / 1000;   //秒级时间戳，10位数
            System.out.println(timestamp1 +"    "+ new Date(timestamp1).toString());
            // 1465142400    Sun Jan 18 06:59:02 CST 1970
            timestamp1 = date1.getTime();               //毫秒级时间戳，13位数
            System.out.println(timestamp1 +"    "+ new Date(timestamp1).toString());
            // 1465142400000    Mon Jun 06 00:00:00 CST 2016

补充一下时间戳相关内容：时间戳有秒级时间戳（10位）、毫秒级时间戳（13位），一般其他语言或数据库用10位秒级时间戳比较多，而Java的Date类默认的时间戳为毫秒级，这也就是为什么Date的构造函数传入秒级时间戳会得到一个奇怪的日期。

使用Java的时间戳插入MySQL的时间戳字段时，要注意先除以1000。因为MySQL默认的时间戳是秒级时间戳。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzMwOTczNDMx_size_16_color_FFFFFF_t_70][]

我使用的是5.6.43版本的MySQL，5.7.25版本也是如此。关于MySQL的时间戳，可以参考：[https://blog.csdn.net/fsp88927/article/details/80662369][https_blog.csdn.net_fsp88927_article_details_80662369]

[https://blog.csdn.net/weter\_drop/article/details/89924451][https_blog.csdn.net_weter_drop_article_details_89924451]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzMwOTczNDMx_size_16_color_FFFFFF_t_70 1][]

另外，使用其他时间戳工具，也是如此，比如我们使用一些时间戳工具网站（[https://tool.lu/timestamp/][https_tool.lu_timestamp]）转换时间戳为日期时，13位的毫秒级会得到错误的结果。

![20200623175239523.png][]

![20200623175302773.png][]

### 八、Date和时间戳（java.sql.Timestamp）的相互转换 ###

//1、将Timestamp转换成Date
            long time = System.currentTimeMillis();
            Timestamp timestamp = new Timestamp(time);
            Date date = new Date(timestamp.getTime());
            System.out.println(date);
            //Tue Jun 23 10:14:27 CST 2020
    
            //2、将Date转换成Timestamp
            date = new Date();
            time = date.getTime();
            //time = time / 1000;
            timestamp = new Timestamp(time);
            System.out.println(timestamp);
            //2020-06-23 10:14:27.636
            //
            date = new Date();
            time = date.getTime();
            timestamp = new Timestamp(time);
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            System.out.println(sdf.format(timestamp));
            //2020-06-23 10:14:27

参考：

[https://howtodoinjava.com/java/date-time/java-date-examples][https_howtodoinjava.com_java_date-time_java-date-examples]

[https://www.javatpoint.com/java-date-to-timestamp][https_www.javatpoint.com_java-date-to-timestamp]

[https://www.cnblogs.com/jpfss/p/8758621.html][https_www.cnblogs.com_jpfss_p_8758621.html]

[https://segmentfault.com/q/1010000000667913][https_segmentfault.com_q_1010000000667913]

[https://www.cnblogs.com/jpfss/p/7132424.html][https_www.cnblogs.com_jpfss_p_7132424.html]

[https://www.iteye.com/blog/tangmingjie2009-1543166][https_www.iteye.com_blog_tangmingjie2009-1543166]

[Apache Commons Lang]: https://mvnrepository.com/artifact/org.apache.commons/commons-lang3
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzMwOTczNDMx_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200623193632793.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzMwOTczNDMx,size_16,color_FFFFFF,t_70
[https_blog.csdn.net_fsp88927_article_details_80662369]: https://blog.csdn.net/fsp88927/article/details/80662369
[https_blog.csdn.net_weter_drop_article_details_89924451]: https://blog.csdn.net/weter_drop/article/details/89924451
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzMwOTczNDMx_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/2020062317564959.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzMwOTczNDMx,size_16,color_FFFFFF,t_70
[https_tool.lu_timestamp]: https://tool.lu/timestamp/
[20200623175239523.png]: https://img-blog.csdnimg.cn/20200623175239523.png
[20200623175302773.png]: https://img-blog.csdnimg.cn/20200623175302773.png
[https_howtodoinjava.com_java_date-time_java-date-examples]: https://howtodoinjava.com/java/date-time/java-date-examples
[https_www.javatpoint.com_java-date-to-timestamp]: https://www.javatpoint.com/java-date-to-timestamp
[https_www.cnblogs.com_jpfss_p_8758621.html]: https://www.cnblogs.com/jpfss/p/8758621.html
[https_segmentfault.com_q_1010000000667913]: https://segmentfault.com/q/1010000000667913
[https_www.cnblogs.com_jpfss_p_7132424.html]: https://www.cnblogs.com/jpfss/p/7132424.html
[https_www.iteye.com_blog_tangmingjie2009-1543166]: https://www.iteye.com/blog/tangmingjie2009-1543166