Java8 of LocalDate LocalTime LocalDateTime family

Foreword

Recently done a lot of statistical functions, and to date this is basic stuff to deal with, a variety, how many days forward, forward a few hours, a few minutes of operation forward, although Java's Calendar This calendar action class can get, but still feel a little hard to write. Sure enough, I found LocalDate LocalTime LocalDateTime this time JAVA8 new class

Introduction

java.util.Date and java.sql.Date is jdk1 began to provide, java.sql.Date inherited java.util.Date, we interact with the database, is generally used java.util.Date class, because java. sql.Date of getHours, getMinutes, gitSeconds these three methods are so written:

    @Deprecated
    public int getHours() {
        throw new java.lang.IllegalArgumentException();
    }
    
    @Deprecated
    public int getMinutes() {
        throw new java.lang.IllegalArgumentException();
    }
    
     @Deprecated
    public int getSeconds() {
        throw new java.lang.IllegalArgumentException();
    }
    
    对应的setXXXX方法也是如出一辙的抛出IllegalArgumentException异常
    例如：
    @Deprecated
    public void setHours(int i) {
        throw new java.lang.IllegalArgumentException();
    }
    并且还带有@Deprecated(废弃)这个注解，看来，java.sql.Date只能显示到：年月日这个级别了，也就是:2019-11-22这种形式的数据
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LocalDate, LocalTime, LocalDateTime introduction

LocalDate,LocalTime,LocalDateTIme这三个类是java8新提供的时间操作类,在java.time包下面.这三个类是从org.joda.time吸收过来的(地方武装的工具类被提成标准部队了).
1.LocalDate是主管：yyyy-MM-dd(2019-11-22)这种形式，也就是只管:年-月-日
2.LocalTime是主管：HH:mm:ss (14:56:23)这种形式，也就是只管:时:分:秒
3.LocalDateTime是主管:yyyy-MM-dd HH:mm:ss 这种形式，也就是只管:年-月-日 时:分:秒(LocalDateTime是由LocalDate和LocalTime组成的)
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1. A method to construct the object

LocalDate,LocaTime,LocalDateTime提供了基本上一致,有以下集中:
now()系列：
    //默认时区
    public static LocalDate now() {
        return now(Clock.systemDefaultZone());
    }
    //自定义时区,例如你可以通过ZoneId.of("America/New_York")使用纽约的时区
    public static LocalDate now(ZoneId zone) {
        return now(Clock.system(zone));
    }
    //自定义时钟,这个有点高深，还没使用过
    public static LocalDate now(Clock clock) {
        Objects.requireNonNull(clock, "clock");
        // inline to avoid creating object and Instant checks
        final Instant now = clock.instant();  // called once
        ZoneOffset offset = clock.getZone().getRules().getOffset(now);
        long epochSec = now.getEpochSecond() + offset.getTotalSeconds();  // overflow caught later
        long epochDay = Math.floorDiv(epochSec, SECONDS_PER_DAY);
        return LocalDate.ofEpochDay(epochDay);
    }

of系列:(这里只列举LocalDate的of)
    //根据年月日构造LocalDate对象,这个地方的dayOfMonth是1-31的取值
    public static LocalDate of(int year, Month month, int dayOfMonth) {
        YEAR.checkValidValue(year);
        Objects.requireNonNull(month, "month");
        DAY_OF_MONTH.checkValidValue(dayOfMonth);
        return create(year, month.getValue(), dayOfMonth);
    }
    //同上，只是都是使用int类型来传递参数了
    public static LocalDate of(int year, int month, int dayOfMonth) {
        YEAR.checkValidValue(year);
        MONTH_OF_YEAR.checkValidValue(month);
        DAY_OF_MONTH.checkValidValue(dayOfMonth);
        return create(year, month, dayOfMonth);
    }
    //这个是定位到一年当中的第几天
    public static LocalDate ofYearDay(int year, int dayOfYear) {
        YEAR.checkValidValue(year);
        DAY_OF_YEAR.checkValidValue(dayOfYear);
        boolean leap = IsoChronology.INSTANCE.isLeapYear(year);
        if (dayOfYear == 366 && leap == false) {
            throw new DateTimeException("Invalid date 'DayOfYear 366' as '" + year + "' is not a leap year");
        }
        Month moy = Month.of((dayOfYear - 1) / 31 + 1);
        int monthEnd = moy.firstDayOfYear(leap) + moy.length(leap) - 1;
        if (dayOfYear > monthEnd) {
            moy = moy.plus(1);
        }
        int dom = dayOfYear - moy.firstDayOfYear(leap) + 1;
        return new LocalDate(year, moy.getValue(), dom);
    }
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2. Specific examples of the use (this is a good thing to get started)

Now the object of acquisition time:

//时间是：2019-11-22
LocaDate now = LocalDate.now();

//时间是：14:43:56
LocalTime now = LocalTime.now();

//时间是：2019-11-22 14:43:56
LocalDateTime now = LocalDateTime.now();
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Customized to the specific use of time

//时间是:2015-12-20
LocalDate localDate = LocalDate.of(2015,12,20);

//时间是：15:36:48
LocalTime localTime = LocalTime.of(15,36,48);

//时间是:2013-09-21 05:56:24
LocalDateTime localDateTime = LocalDateTime.of(2013,9,21,5,58,24);
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Positioning time various conditions

Old iron must pay attention to: after all LocalDate various operations, he returns a new LocalDate objects, so you have to then this new object ah, if you do not then the object, you will see no effect, like this good programming chain

我们在开发中可能遇到各种条件的定位时间:本月的第一天，本月的最后一天，本月每周的周一，本月每周的周三，本年度的第9月的第二天，或者哪一年的上述各种情况：

//我们随便拿个时间做实验，以求做到一般化处理，就拿2019-10-22日来处理吧
LocalDate localDate = LocalDate.of(2019,10,22);
//**老铁们一定要注意：凡是LocalDate各种操作之后，他都返回一个新的LocalDate对象，所以，你要接着这个新对象啊，你要是不用对象接着，那么就会看到不起作用，这样子好链式编程**

//1.获取本月的第一天,输出：2019-10-01
localDate = localDate.with(TemporalAdjusters.firstDayOfMonth())

//2.获取本月的最后一天,输出:2019-10-31
localDate = localDate.with(TemporalAdjusters.lastDayOfMonth());

//3.本年第一天，输出:2019-01-01
localDate = localDate.with(TemporalAdjusters.firstDayOfYear());

//4.本年最后一天，输出：2019-12-31
localDate = localDate.with(TemporalAdjusters.lastDayOfYear());

//5.下一个周几的操作，输出：2019-10-24
//注意，2019-10-22是周二，所以下一个周四就是2019-10-24,如果是下一个周一，那就是:2019-10-28了
//当然也有对应的previes方法,就是上一个周几
localDate = localDate.with(TemporalAdjusters.next(DayOfWeek.THURSDAY));
localDate = localDate.with(TemporalAdjusters.previes(DayOfWeek.THURSDAY));

//6.本月第2周的周五，输出是:2019-10-11
localDate = localDate.with(TemporalAdjusters.dayOfWeekInMonth(2,DayOfWeek.FRIDAY));

//7.还有下一个月的第一天，输出是:2019-11-01，当然还有下一年
localDate = localDate.with(TemporalAdjusters.firstDayOfNextMonth());

//8.加一天,输出是：2019-10-23
localDate = localDate.plusDays(1L);

//9.加一周，输出是：2019-10-29(即使是跨年和跨月，也会正确加的，不用担心)
localDate = localDate.plusWeeks(1L);

//10.加一个月,输出是：2019-11-22（下一月没有31号这种情况，他们会帮我们处理的）,例如:2019-10-31加一个月，返回：2019-11-30(放心，JDK都是进过各种验证的，不会出现人不能理解的错误的)
localDate = localDate.plusMonths(1L);
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Similarly, and LocalDateTime LocalTime may also be according to the above method of addition and subtraction hours, minutes, seconds, etc. Operation

3. Comparison of time

Prior to this time are relatively getTime then compare it on the line, now LocalDate, LocalTime, LocalDateTime provides isBefore, isAfter method

LocalDate first = LocalDate.now();
LocalDate second = LocalDate.of(2015,12,25);
first.isBefore(second);//返回：false
first.isAfter(second);//返回：true
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4. the date string formatting

We can not avoid the often need to format the date string, this area Local family is also doing well

//输出为：2019-10-22
localDate.format(DateTimeFormatter.ofPattern("yyyy-MM-dd"));
不用像之前还要一个SimpleDateFormatter了
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5. wander Finally, struggling, is java.util.Date and LocalDate, LocalTime, LocalDateTime system conversion is no direct way, no way, a supplement of their own

    //java.util.Date类型转LocalDateTime
    public static LocalDateTime dateToLocalDateTime(Date date) {
        Instant instant = date.toInstant();
        ZoneId zoneId = ZoneId.systemDefault();
        return instant.atZone(zoneId).toLocalDateTime();
    }
    
    //java.time.LocalDateTime转java.util.Date
    public static Date localDateTimeToDate(LocalDateTime localDateTime) {
        ZoneId zoneId = ZoneId.systemDefault();
        ZonedDateTime zdt = localDateTime.atZone(zoneId);
        return Date.from(zdt.toInstant());
    }
    
    有了LocalDateTime,你就可以操作获取LocalDate，LocalTime了，当然也有转Date<-->LocalDate  Date<-->LocalTime的操作，
    在这个地方就不一一列举了!,其实就是instant.atZone(zoneId).toLocalDateTime()修改这句话就行
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6. I posted an example of the operation

        String sqlFormat = "drop table gsms_phone_detection_0101";

        LocalDate startDate = LocalDate.of(2012, 1, 1);
        LocalDate endDate = LocalDate.of(2012, 12, 31);
        List<String> result = Stream.iterate(startDate, localDate -> localDate.plusDays(1L))
                .limit(ChronoUnit.DAYS.between(startDate, endDate) + 1)
                .map(localDate -> localDate.format(DateTimeFormatter.ofPattern("MMdd")))
                .map(tableSuffix -> sqlFormat.replaceAll("0101",tableSuffix))
                .collect(Collectors.toList());
        Files.write(Paths.get("/home/liuxu/Pictures/gsms_ded_red_det_verify_xxxx.sql"),result);
        
        这是我生成删除按照日分表的sql语句,(不会写存储过程或者函数，也没有功夫探索了)
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