java8日期时间LocalDate,LocalTime,LocalDateTime精讲

朴灿烈づ我的快乐病毒、 2022-09-11 08:15 207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。

package com.wq.study.java8.date;
    
    import java.time.Clock;
    import java.time.Instant;
    import java.time.LocalDate;
    import java.time.LocalDateTime;
    import java.time.LocalTime;
    import java.time.Month;
    import java.time.MonthDay;
    import java.time.OffsetDateTime;
    import java.time.ZoneOffset;
    import java.time.Period;
    import java.time.YearMonth;
    import java.time.ZoneId;
    import java.time.ZonedDateTime;
    import java.time.format.DateTimeFormatter;
    import java.time.temporal.ChronoUnit;
    import java.util.Date;
    
    public class DateTest { 
        
        //获取今天的日期
        public void getCurrentDate(){ 
            LocalDate today = LocalDate.now();
            System.out.println("Today's Local date : " + today);
            
            //这个是作为对比
            Date date = new Date();
            System.out.println(date);
        }
        
        //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 Month : %d day : %d t %n", year, month, day);
        }
        
        //处理特定日期
        public void handleSpecilDate(){ 
            LocalDate dateOfBirth = LocalDate.of(2018, 01, 21);
            System.out.println("The specil date is : " + dateOfBirth);
        }
        
        //判断两个日期是否相等
        public void compareDate(){ 
            LocalDate today = LocalDate.now();
            LocalDate date1 = LocalDate.of(2018, 01, 21);
            
            if(date1.equals(today)){ 
                System.out.printf("TODAY %s and DATE1 %s are same date %n", today, date1);
            }
        }
        
        //处理周期性的日期
        public void cycleDate(){ 
            LocalDate today = LocalDate.now();
            LocalDate dateOfBirth = LocalDate.of(2018, 01, 21);
            
            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");
            }
        }
        
        //获取当前时间
        public void getCurrentTime(){ 
            LocalTime time = LocalTime.now();
            System.out.println("local time now : " + time);
        }
        
        //增加小时
        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);
        }
        
        //如何计算一周后的日期
        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);
        }
        
        //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);
        }
        
        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);
        }
        
        //如何用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(2018, 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");
            }
        }
        
        //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);
        }
        
        //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);
        }
        
        //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("2018 is not a Leap year");
            }
        }
        
        //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(2018, Month.MAY, 14);
            
            Period periodToNextJavaRelease = Period.between(today, java8Release);
            
            System.out.println("Months left between today and Java 8 release : "
                                               + periodToNextJavaRelease.getMonths() );
        }
        
        // 包含时差信息的日期和时间
        public void ZoneOffset(){ 
            LocalDateTime datetime = LocalDateTime.of(2018, 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);
        }
        
        // 获取时间戳
        public void getTimestamp(){ 
            Instant timestamp = Instant.now();
            System.out.println("What is value of this instant " + timestamp);
        }
    
        // 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 = "20180210";
            LocalDate formatted = LocalDate.parse(dayAfterTommorrow, DateTimeFormatter.BASIC_ISO_DATE);
            System.out.printf("Date generated from String %s is %s %n", dayAfterTommorrow, formatted);
        }
        
        public static void main(String[] args) { 
            DateTest dt = new DateTest();
            
            dt.formateDate();
        }
    
    }