Java8新特性六：New Date-Time API | Java提升营

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Java8新特性六：New Date-Time API

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Java 8中引入了新的Date-Time API，解决了旧的日期时间API的以下缺点：

  • 线程不安全问题：旧的 java.util.Date 是线程不安全的，而 新的 Date-Time API 是不可变的且没有提供setter方法
  • 操作单调：旧API仅提供了少量的方法去操作时间，而新的API提供了许多日期操作

Java 8在java.time包下引入了新的Date-Time API，其中最重要的类是：

  • Local ：简化版的Date-Time API，没有时区处理的复杂性。
  • Zoned ：专门用于处理各种时区的Date-Time API。
  1. LocalDate / LocatTime 和 LocalDateTime
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// 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 foramatted 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 repulic day :"+date2); 
   
    // printing date with current time. 
    LocalDateTime specificDate = current.withDayOfMonth(24).withYear(2016); 
  
    System.out.println("specfic date with current time : "+specificDate); 
} 
  
    // Driver code 
    public static void main(String[] args)  
    { 
        LocalDateTimeApi(); 
    } 
}

输出：

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the current date is 2020-04-09
the current time is 06:21:10.409
current date and time : 2020-04-09T06:21:10.410
in foramatted manner 09-04-2020 06:21:10
Month : APRIL day : 9 seconds : 10
the repulic day :1950-01-26
specfic date with current time : 2016-04-24T06:21:10.410
  1. Zoned date-time API
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// 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);  
    
      OffsetDateTime dateTime = OffsetDateTime.now();

      System.out.println("formatted current Date Time : "+ dateTime.format(format1)); 

      // 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：

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formatted current Date and Time : 09-04-2020 06:21:13
formatted current Date Time : 09-04-2020 06:21:13
the current zone is Etc/UTC
tokyo time zone is 2020-04-09T15:21:13.220+09:00[Asia/Tokyo]
formatted tokyo time zone 09-04-2020 15:21:13
  1. Period和Duration
  • Period：表示一段时间的年、月、日，并使用between()方法获取两个日期之间的差作为Period 对象返回
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LocalDate startDate = LocalDate.of(2018, 2, 20);
LocalDate endDate = LocalDate.of(2020, 1, 15);
 
Period period = Period.between(startDate, endDate);

可以从Period对象中获取日期单元，使用getYears()、getMonhs()、getDays()方法。

还可以通过Period的isNegative()来判断日期的大小。

  • Duration：表示秒或纳秒时间间隔，适合处理较短的时间，需要更高的精确性。我们能使用between()方法比较两个瞬间的差
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Instant start = Instant.parse("2020-04-03T10:15:30.00Z");
Instant end = Instant.parse("2020-04-03T10:16:30.00Z");
         
Duration duration = Duration.between(start, end);

那么我们能使用getSeconds() 或 getNanoseconds() 方法获取时间单元的值

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duration.getSeconds();
duration.getNanoseconds();
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// 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 checkingDuraion() {   
  
        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("duraion gap between time1 & time2 is " + gap); 
} 
  
    // Driver code 
    public static void main(String[] args) { 
        checkingPeriod(); 
        checkingDuraion(); 
    } 
}

输出：

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gap between dates is a period of P3Y3M28D
the current time is 06:21:18.248
after adding five hours of duration 11:21:18.248
duraion gap between time1 & time2 is PT-5H
  1. ChronoUnits枚举： Java 8中添加了java.time.temporal.ChronoUnit枚举，以替换旧API中用于表示日、月等等的整数值。
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// 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：

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current date is :2020-04-09
next to next year is 2020-04-09
the next month is 2020-05-09
next week is 2020-04-16
20 years after today 2020-04-09
  1. TemporalAdjuster：用于执行各种与日期相关的操作。
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// 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 satuday 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

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the current date is 2020-04-09
firstDayOfNextMonth : 2020-05-01
next satuday from now is 2020-04-14
firstDayOfMonth : 2020-04-01
lastDayOfMonth : 2020-04-30
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