java8新特性：时间与日期的处理

太过爱你忘了你带给我的痛 2021-06-10 20:40 497阅读 0赞

## 简介 ##

> 伴随 lambda表达式、 streams 以及一系列小优化，Java 8 推出了全新的日期时间API。
> 
> Java处理日期、日历和时间的不足之处：将 java.util.Date 设定为可变类型，以及 SimpleDateFormat的非线程安全使其应用非常受限。然后就在 java8 上面增加新的特性。
> 
> 全新API的众多好处之一就是，明确了日期时间概念，例如： 瞬时（instant）、 长短（duration）、 日期、 时间、 时区和周期。
> 
> 同时继承了Joda库按人类语言和计算机各自解析的时间处理方式。不同于老版本，新API基于ISO标准日历系统，java.time包下的所有类都是不可变类型而且线程安全。

## 关键类 ##

*  Instant：瞬时实例。
 *  LocalDate：本地日期，不包含具体时间 例如：2014-01-14 可以用来记录生日、纪念日、加盟日等。
 *  LocalTime：本地时间，不包含日期。
 *  LocalDateTime：组合了日期和时间，但不包含时差和时区信息。
 *  ZonedDateTime：最完整的日期时间，包含时区和相对UTC或格林威治的时差。

> 新API还引入了 ZoneOffSet 和 ZoneId 类，使得解决时区问题更为简便。解析、格式化时间的  
> DateTimeFormatter\\ 类也全部重新设计。

## 实战 ##

### 1.获取今天的日期 ###

@Test
        public void getCurrentDate(){
            LocalDate today = LocalDate.now();
            System.out.println("Java8's Local date : " + today);
    
            //这个是老版本
            Date date = new Date();
            System.out.println("Old version date : "+date);
        }

![在这里插入图片描述][20210430175527114.png]

### 2. 获取年、月、日信息 ###

public void getDetailDate(){
            LocalDate today = LocalDate.now();
            int year = today.getYear();
            int month = today.getMonthValue();
            int day = today.getDayOfMonth();
    
            System.out.printf("Year : %d  \nMonth : %d  \nday : %d ", year, month, day);
        }

![在这里插入图片描述][20210430175337557.png]

### 3. 处理特定日期 ###

public void handleSpecilDate(){
            LocalDate dateOfBirth = LocalDate.of(2020, 01, 23);
            System.out.println("The specil date is : " + dateOfBirth);
        }

![在这里插入图片描述][20210430175632164.png]

### 3. 判断两个日期是否相等 ###

public void compareDate(){
            LocalDate today = LocalDate.now();
            LocalDate date1 = LocalDate.of(2020, 01, 23);
    
            if(date1.equals(today)){
                System.out.printf("TODAY %s and DATE1 %s are same date %n", today, date1);
            }else{
                System.out.printf("TODAY %s and DATE1 %s are not same date %n", today, date1);
            }
        }

![在这里插入图片描述][20210430175758558.png]

### 4. 处理周期性的日期 ###

public void cycleDate(){
            LocalDate today = LocalDate.now();
            LocalDate dateOfBirth = LocalDate.of(2020, 01, 23);
    
    		//某月某日
            MonthDay birthday = MonthDay.of(dateOfBirth.getMonth(), dateOfBirth.getDayOfMonth());
            MonthDay currentMonthDay = MonthDay.from(today);
    
            if(currentMonthDay.equals(birthday)){
                System.out.println("Many Many happy returns of the day !!");
            }else{
                System.out.println("Sorry, today is not your birthday");
            }
        }

![在这里插入图片描述][20210430180027166.png]

### 5. 获取当前时间 ###

public void getCurrentTime(){
            LocalTime time = LocalTime.now();
            System.out.println("local time now : " + time);
        }

![在这里插入图片描述][20210430180053514.png]

### 6. 时间延迟或提前两小时 ###

public void plusHours(){
            LocalTime time = LocalTime.now();
            LocalTime newTime = time.plusHours(2); // 增加两小时
            System.out.println("Time after 2 hours : " +  newTime);
    		
            newTime = time.plusHours(-2);// 减少两小时
            //newTime = time.minusHours(2);//当然也可以用minusHours方法实现上行代码同样效果
            System.out.println("Time before 2 hours : " +  newTime);
        }

![在这里插入图片描述][20210430180115917.png]

### 7. 计算一周后的日期 ###

public void nextWeek(){
            LocalDate today = LocalDate.now();
            LocalDate nextWeek = today.plus(1, ChronoUnit.WEEKS);
            System.out.println("Today is : " + today);
            System.out.println("Date after 1 week : " + nextWeek);
        }

![在这里插入图片描述][20210430180203698.png]

### 8. 计算一年前或一年后的日期 ###

public void minusDate(){
            LocalDate today = LocalDate.now();
            LocalDate previousYear = today.minus(1, ChronoUnit.YEARS);
            System.out.println("Date before 1 year : " + previousYear);
    
            LocalDate nextYear = today.plus(1, ChronoUnit.YEARS);
            System.out.println("Date after 1 year : " + nextYear);
        }

![在这里插入图片描述][20210430180236856.png]

### 9. 获取时钟 ###

public void clock(){
            // 根据系统时间返回当前时间并设置为UTC。
            Clock clock = Clock.systemUTC();
            System.out.println("Clock : " + clock);
    
            // 根据系统时钟区域返回时间
            Clock defaultClock = Clock.systemDefaultZone();
            System.out.println("Clock : " + clock);
        }

![在这里插入图片描述][202104301803079.png]

### 10. 用Java判断日期是早于还是晚于另一个日期 ###

public void isBeforeOrIsAfter(){
            LocalDate today = LocalDate.now();
    
            LocalDate tomorrow = LocalDate.of(2020, 1, 29);
            if(tomorrow.isAfter(today)){
                System.out.println("Tomorrow comes after today");
            }
    
            LocalDate yesterday = today.minus(1, ChronoUnit.DAYS);
    
            if(yesterday.isBefore(today)){
                System.out.println("Yesterday is day before today");
            }
        }

![在这里插入图片描述][20210430180354620.png]

### 11. 时区处理 ###

public void getZoneTime(){
            //设置时区
            ZoneId america = ZoneId.of("America/New_York");
    
            LocalDateTime localtDateAndTime = LocalDateTime.now();
    
            ZonedDateTime dateAndTimeInNewYork  = ZonedDateTime.of(localtDateAndTime, america );
            System.out.println("现在的日期和时间在特定的时区 : " + dateAndTimeInNewYork);
        }

![在这里插入图片描述][20210430180415797.png]

### 12. 使用 YearMonth类处理特定的日期 ###

public void checkCardExpiry(){
            YearMonth currentYearMonth = YearMonth.now();
            System.out.printf("Days in month year %s: %d%n", currentYearMonth, currentYearMonth.lengthOfMonth());
    
            YearMonth creditCardExpiry = YearMonth.of(2028, Month.FEBRUARY);
            System.out.printf("Your credit card expires on %s %n", creditCardExpiry);
        }

![在这里插入图片描述][20210430180440869.png]

### 13. 检查闰年 ###

public void isLeapYear(){
            LocalDate today = LocalDate.now();
            if(today.isLeapYear()){
                System.out.println("This year is Leap year");
            }else {
                System.out.println("2020 is not a Leap year");
            }
        }

![在这里插入图片描述][20210430180512513.png]

### 14. 计算两个日期之间的天数和月数 ###

public void calcDateDays(){
            LocalDate today = LocalDate.now();
    
            LocalDate java8Release = LocalDate.of(2020, Month.MAY, 14);
    
            Period periodToNextJavaRelease = Period.between(today, java8Release);
    
            System.out.println("Months left between today and Java 8 release : "
                    + periodToNextJavaRelease.getMonths() );
        }

![在这里插入图片描述][20210430180533143.png]

### 15. 包含时差信息的日期和时间 ###

public void ZoneOffset(){
            LocalDateTime datetime = LocalDateTime.of(2020, Month.FEBRUARY, 14, 19, 30);
            ZoneOffset offset = ZoneOffset.of("+05:30");
            OffsetDateTime date = OffsetDateTime.of(datetime, offset);
            System.out.println("Date and Time with timezone offset in Java : " + date);
        }

![在这里插入图片描述][20210430180550674.png]

### 16. 获取时间戳 ###

public void getTimestamp(){
            Instant timestamp = Instant.now();
            System.out.println(""What's the value of this instant : "" + timestamp);
        }

![在这里插入图片描述][20210430180734658.png]

### 17. 使用预定义的格式化工具去解析或格式化日期 ###

public void formateDate(){
            String dayAfterTommorrow = "20200123";
            LocalDate formatted = LocalDate.parse(dayAfterTommorrow, DateTimeFormatter.BASIC_ISO_DATE);
            System.out.printf("Date generated from String %s is %s %n", dayAfterTommorrow, formatted);
        }

![在这里插入图片描述][20210430180822548.png]

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