Java 8 中的新日期时间 API

Java 8 中引入了新的日期时间 API，以克服旧日期时间 API 的以下缺点：

1. 不是线程安全的：与不是线程安全的旧Java.util.Date 不同，新的日期时间 API 是不可变的并且没有 setter 方法。
2. 更少的操作：在旧 API 中只有很少的日期操作，但新 API 为我们提供了许多日期操作。

Java 8 在Java.time 包下引入了一个新的日期时间 API，其中最重要的类是：

1. Local ：简化的日期时间 API，没有复杂的时区处理。
2. Zoned ：处理各种时区的专用日期时间 API。

• LocalDate/LocatTime和LocalDateTime API：在不需要时区时使用它。

Java

// Java code for LocalDate
// / LocalTime Function
import java.time.*;
import java.time.format.DateTimeFormatter;
  
public class Date {
 
public static void LocalDateTimeApi()
{
  
    // the current date
    LocalDate date = LocalDate.now();
    System.out.println("the current date is "+
                        date);
  
  
    // the current time
    LocalTime time = LocalTime.now();
    System.out.println("the current time is "+
                        time);
      
  
    // will give us the current time and date
    LocalDateTime current = LocalDateTime.now();
    System.out.println("current date and time : "+
                        current);
  
  
    // to print in a particular format
    DateTimeFormatter format =
      DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss"); 
   
    String formatedDateTime = current.format(format); 
    
    System.out.println("in formatted manner "+
                        formatedDateTime);
  
  
    // printing months days and seconds
    Month month = current.getMonth();
    int day = current.getDayOfMonth();
    int seconds = current.getSecond();
    System.out.println("Month : "+month+" day : "+
                        day+" seconds : "+seconds);
  
    // printing some specified date
    LocalDate date2 = LocalDate.of(1950,1,26);
    System.out.println("the republic day :"+date2);
  
    // printing date with current time.
    LocalDateTime specificDate =
        current.withDayOfMonth(24).withYear(2016);
 
    System.out.println("specific date with "+
                       "current time : "+specificDate);
}
 
    // Driver code
    public static void main(String[] args)
    {
        LocalDateTimeApi();
    }
}

输出

the current date is 2021-09-23
the current time is 20:52:39.954238
current date and time : 2021-09-23T20:52:39.956909
in formatted manner 23-09-2021 20:52:39
Month : SEPTEMBER day : 23 seconds : 39
the republic day :1950-01-26
specific date with current time : 2016-09-24T20:52:39.956909

• Zoned date-time API : 当需要考虑时区时使用它

Java

// Java code for Zoned date-time API
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
 
public class Zone {
 
// Function to get Zoned Date and Time
public static void ZonedTimeAndDate()
{
    LocalDateTime date = LocalDateTime.now();
    DateTimeFormatter format1 =
      DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss");
     
    String formattedCurrentDate = date.format(format1);
     
    System.out.println("formatted current Date and"+
                      " Time : "+formattedCurrentDate);
 
    // to get the current zone
    ZonedDateTime currentZone = ZonedDateTime.now();
    System.out.println("the current zone is "+
                        currentZone.getZone());
 
    // getting time zone of specific place
    // we use withZoneSameInstant(): it is
    // used to return a copy of this date-time
    // with a different time-zone, 
    // retaining the instant.
    ZoneId tokyo = ZoneId.of("Asia/Tokyo");
 
    ZonedDateTime tokyoZone =
            currentZone.withZoneSameInstant(tokyo);
                   
    System.out.println("tokyo time zone is " +
                        tokyoZone);
 
    DateTimeFormatter format =
        DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss");
     
    String formatedDateTime = tokyoZone.format(format);
 
    System.out.println("formatted tokyo time zone "+
                        formatedDateTime);
     
}
     
    // Driver code
    public static void main(String[] args)
    {
         
        ZonedTimeAndDate();
         
    }
}

输出：

formatted current Date and Time : 09-04-2018 06:21:13
the current zone is Etc/UTC
tokyo time zone is 2018-04-09T15:21:13.220+09:00[Asia/Tokyo]
formatted tokyo time zone 09-04-2018 15:21:13

• 期间和持续时间类：
  Period ：它处理基于日期的时间量。
  持续时间：它处理基于时间的时间量。

Java

// Java code for period and duration
import java.time.LocalDate;
import java.time.LocalTime;
import java.time.Month;
import java.time.Duration;
import java.time.Period;
 
public class Geekforgeeks {
 
    public static void checkingPeriod()
    {
        LocalDate date1 = LocalDate.now();
 
        LocalDate date2 =
            LocalDate.of(2014, Month.DECEMBER, 12);
 
        Period gap = Period.between(date2, date1);
        System.out.println("gap between dates "+
                           "is a period of "+gap);
}
 
    // Function to check duration
    public static void checkingDuration()
    { 
 
        LocalTime time1 = LocalTime.now();
        System.out.println("the current time is " +
                            time1);
 
        Duration fiveHours = Duration.ofHours(5);
 
        // adding five hours to the current
        // time and storing it in time2
        LocalTime time2 = time1.plus(fiveHours);
 
        System.out.println("after adding five hours " +
                           "of duration " + time2);
 
        Duration gap = Duration.between(time2, time1);
        System.out.println("duration gap between time1" +
                           " & time2 is " + gap);
}
 
    // Driver code
    public static void main(String[] args)
    {
        checkingPeriod();
        checkingDuration();
    }
}

输出

gap between dates is a period of P6Y6M25D
the current time is 18:34:24.813548
after adding five hours of duration 23:34:24.813548
duration gap between time1 & time2 is PT-5H

• ChronoUnits Enum ： Java 8 中添加了Java .time.temporal.ChronoUnit 枚举，以替换旧 API 中用于表示日、月等的整数值。

Java

// Java code for ChronoUnits Enum
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
 
public class Geeksforgeeks {
 
    // Function to check ChronoUnit
    public static void checkingChronoEnum()
    {
        LocalDate date = LocalDate.now();
        System.out.println("current date is :" +
                            date);
     
        // adding 2 years to the current date
        LocalDate year =
             date.plus(2, ChronoUnit.YEARS);
         
        System.out.println("next to next year is " +
                            year);
             
        // adding 1 month to the current data
        LocalDate nextMonth =
                  date.plus(1, ChronoUnit.MONTHS);
         
        System.out.println("the next month is " +
                            nextMonth);
     
        // adding 1 week to the current date
        LocalDate nextWeek =
                  date.plus(1, ChronoUnit.WEEKS);
         
        System.out.println("next week is " + nextWeek);
     
        // adding 2 decades to the current date
        LocalDate Decade =
                  date.plus(2, ChronoUnit.DECADES);
                   
        System.out.println("20 years after today " +
                            Decade);
    }
     
    // Driver code
    public static void main(String[] args) {
     
        checkingChronoEnum();
         
    }
}

输出：

current date is :2018-04-09
next to next year is 2020-04-09
the next month is 2018-05-09
next week is 2018-04-16
20 years after today 2038-04-09

• TemporalAdjuster ：用于执行各种与日期相关的操作。

Java

// Java code Temporal Adjuster
import java.time.LocalDate;
import java.time.temporal.TemporalAdjusters;
import java.time.DayOfWeek;
 
public class Geek
{
 
    // Function to check date and time
    // according to our requirement
    public static void checkingAdjusters()
    {
 
        LocalDate date = LocalDate.now();
        System.out.println("the current date is "+
                            date);
 
        // to get the first day of next month
        LocalDate dayOfNextMonth =
              date.with(TemporalAdjusters.
                        firstDayOfNextMonth());
     
        System.out.println("firstDayOfNextMonth : " +
                            dayOfNextMonth );
 
        // get the next saturday
        LocalDate nextSaturday =
                date.with(TemporalAdjusters.
                          next(DayOfWeek.SATURDAY));
         
        System.out.println("next saturday from now is "+
                            nextSaturday);
 
        // first day of current month
        LocalDate firstDay =
                  date.with(TemporalAdjusters.
                  firstDayOfMonth());
                                    
        System.out.println("firstDayOfMonth : " +
                            firstDay);
 
        // last day of current month    
        LocalDate lastDay =
                  date.with(TemporalAdjusters.
                            lastDayOfMonth());
         
        System.out.println("lastDayOfMonth : " +
                            lastDay);
}
     
    // Driver code
    public static void main(String[] args)
    {
 
        checkingAdjusters();
    }
}

输出

the current date is 2021-07-09
firstDayOfNextMonth : 2021-08-01
next saturday from now is 2021-07-10
firstDayOfMonth : 2021-07-01
lastDayOfMonth : 2021-07-31