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前言：字字看来皆是血，几天辛苦不寻常,花了几天把LocalDate的方法研究了个遍，其中不乏自己的思考
/**
*
*/
package com.ljh.myo2o.dao;
import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.Month;
import java.time.Period;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoField;
import java.time.temporal.ChronoUnit;
import java.time.temporal.TemporalAdjusters;
import java.time.temporal.TemporalQueries;
import java.time.temporal.ValueRange;
import java.util.Arrays;
import java.util.Locale;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* @description:
* @author :林建辉
* @CreateTime:2018-11-23 02:23:41
*/
public class DateAndTimeDemo {
private Logger logger = LoggerFactory.getLogger(DateAndTimeDemo.class);
/**
* discription:
*
* @author:林建辉
* @createTime:2018-11-23 02:23:41
* @param args
*/
public static void main(String[] args) {
// 从默认时区的系统时钟获取当前日期
// LocalDate:只包含日期而没有时间
// 该类重写了toString()方法,所以打印的时候是以yyyy-MM-dd 格式输出
LocalDate today = LocalDate.now();
// 今天的日期是: 2018-11-23
System.out.println("今天的日期是: " + today);
// 从指定的年月日中获取LocalDate实例
// 指定的日必须对年和月有效否则将抛出DateTimeException
// 此方法有一个重载，就是第二个参数为Month枚举
LocalDate specifiedDate = LocalDate.of(2018, 1, 1);
LocalDate sDate = LocalDate.of(2018, Month.JANUARY, 1);
// 判断两个日期是否相等就用equals方法，LocalDate类重写了equals方法
System.out.println(specifiedDate.equals(sDate));// true
// 如果想知道某一年的第340天是几月几号，可以使用下面的方法
LocalDate date = LocalDate.ofYearDay(2018, 340);
System.out.println(date);// 2018-12-06
// 如果想知道今天是一年中的第几天，可以使用下面的方法，其它同理
int dayOfYear = date.getDayOfYear();
int dayOfMonth = date.getDayOfMonth();
System.out.println(dayOfYear + "__" + dayOfMonth);
// 下面是java.util.time包中唯二的两个枚举
// 不仅有枚举值，也包含一些计算方法如：plus/minus/firstMonthOfQuarter
DayOfWeek dayOfWeek = date.getDayOfWeek();
Month month = date.getMonth();
// 获取月份可以使用以下方法
int monthValue = month.getValue();
int monthValue2 = date.getMonthValue();
// 获取该月份有多少天
date.lengthOfMonth();
month.length(date.isLeapYear());// leap year 闰年
// EpochDay:纪元日 ，第0天是1970-01-01天，负数代表早些日子
long epochDayNums = date.toEpochDay();
LocalDate.ofEpochDay(epochDayNums);
// Chronology:年表
// LocalDate dateNow = date.getChronology().dateNow();
// TemporalAccessor是所有时间类以及时间接口的父类
// LocalDate from = LocalDate.from(TemporalAccessor temporal);
// System.out.println(LocalDateTime.now().toString().replace("T", " "));
// 静态方法的引用中的返回值类型就是功能函数里的泛型，该静态方法的参数就是功能函数中方法的参数
// TemporalQuery<LocalDate> q=LocalDate::from;
// 其内部就是调用其重载方法
LocalDate parse1 = LocalDate.parse("2018-11-11");
LocalDate parse2 = LocalDate.parse("2018-11-11", DateTimeFormatter.ISO_LOCAL_DATE);
System.out.println(parse1);
System.out.println(parse2);
// 虽然不知道有什么用,用于判断
boolean supportedChronoField = date.isSupported(ChronoField.DAY_OF_MONTH);
boolean supportedChronoUnit = date.isSupported(ChronoUnit.YEARS);
System.out.println(supportedChronoField);
System.out.println(supportedChronoUnit);
// 获取某个日期字段的有效范围值
ValueRange range = date.range(ChronoField.DAY_OF_MONTH);
System.out.println(range);// 1 - 31
// int i = date.get(ChronoField.DAY_OF_MONTH);//6
// 反正也不知道啥用
// 哪种写法更牛逼点
/*
* for (ChronoField c : ChronoField.values()) { if (date.isSupported(c))
* { if ("EpochDayProlepticMonth".contains(c.toString())) {
* System.out.println(date.getLong(c)+"--"+c); }else {
* System.out.println(date.get(c)+"--"+c); }
*
* } }
*/
Arrays.asList(ChronoField.values()).forEach((c) -> {
if (date.isSupported(c)) {
if ("EpochDayProlepticMonth".contains(c.toString())) {
System.out.println(date.getLong(c) + "--" + c);
} else {
System.out.println(date.get(c) + "--" + c);
}
}
});
// with系列方法
/*
* LocalDate with(TemporalAdjuster adjuster) LocalDate
* with(TemporalField field, long newValue) LocalDate withYear(int year)
* LocalDate withMonth(int month) LocalDate withDayOfYear(int dayOfYear)
* 由于LocalDate 是final类，每次的修改都要用变量保存起来 示例表示返回7月份的最后一天的日期 result =
* localDate.with(JULY).with(lastDayOfMonth());
*/
// LocalDate withDayOfMonth =
// date.with(Month.JULY).withDayOfMonth(Month.JULY.length(date.with(Month.JULY).isLeapYear()));
LocalDate lastDateOfJuly = date.with(Month.JULY);
lastDateOfJuly = lastDateOfJuly.withDayOfMonth(lastDateOfJuly.lengthOfMonth());
System.out.println(lastDateOfJuly);
/*
* // these two lines are equivalent
* Period period = start.until(end);
* Period.between(start, end);
*/
/*
* plus和minus系列方法: Period类和Duration类实现了TemporalAmount接口
* ChronoUnit实现了TemporalUnit接口 LocalDate plus(TemporalAmount
* amountToAdd) LocalDate plus(long amountToAdd, TemporalUnit unit)
* LocalDate plusYears(long yearsToAdd) LocalDate plusMonths(long
* monthsToAdd) LocalDate plusWeeks(long weeksToAdd) LocalDate
* plusDays(long daysToAdd)
*/
Period period = Period.between(LocalDate.of(2018, 12, 7), LocalDate.of(2018, 12, 31));
LocalDate plusDate = date.plus(period);
System.out.println(plusDate);
System.out.printf("LocalDate precision is %s%n",
date.query(TemporalQueries.precision()));
/*
* 插曲
StringBuilder sb = new StringBuilder();//实现了Appendable接口
//格式输出到Appendable,以中国的格式输出
Formatter formatter = new Formatter(sb, Locale.CHINA);
//格式输出语法： %[argument_index$][flags][width][.precision]conversion
formatter.format("%4$2s%3$2s%2$2s%1$2s", "a", "b", "c", "d");
System.out.println(formatter.out());
formatter.format(Locale.PRC, "e = %+.4f", Math.E);
System.out.println(formatter.out());
formatter.close();
String format = String.format("hello,%s","world!");
System.out.println(format);
System.out.format("hello,%s","world!");*/
//没有得到预期效果
LocalDate newDate =(LocalDate)date.adjustInto(LocalDate.of(2018, 12, 31));
System.out.println("newDate:"+newDate);
//这样调整就行
LocalDate with = LocalDate.now().with(TemporalAdjusters.next(DayOfWeek.MONDAY));
System.out.println(with);//今天的日期为25号，调整后的日期为2018-11-26
//计算距离2019-01-30有多少天
long until = LocalDate.now().until(LocalDate.of(2019, 1, 30), ChronoUnit.DAYS);
System.out.println(until);//66
//until 的重载
Period period2 = LocalDate.now().until(LocalDate.of(2019, 1, 30));
System.out.println(period2.getDays());//为什么是5,这个方法有bug
/*
* 从源码里可以看到，格式化就是调用DateTimeFormatter.format()方法
* public String format(DateTimeFormatter formatter) {
Objects.requireNonNull(formatter, "formatter");
return formatter.format(this);
}
*/
//写个示例而已，虽然没有必要这么做
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("yyyy-MM-dd",Locale.CHINA);
String format = LocalDate.now().format(formatter);
System.out.println(format);
/*
* atTime系列方法：用于调整时间，给日期加时间
* LocalDateTime atTime(LocalTime time)
* LocalDateTime atTime(int hour, int minute)
* LocalDateTime atTime(int hour, int minute, int second)
* LocalDateTime atTime(int hour, int minute, int second, int nanoOfSecond)
* OffsetDateTime atTime(OffsetTime time)
*/
LocalDateTime atTime = LocalDate.now().atTime(10, 25);
System.out.println(atTime);//2018-11-25T10:25
//打印出来我们发现时间和日期多了个T,不符合中国的日期标准，格式化一下
String format2 = atTime.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME);
System.out.println(format2);//2018-11-25T10:25:00
//打印出来我们发现，使用预定格式的格式化器还是有个T，只是多了秒
//当预定格式的格式化器也无法满足的时候，使用自定义的格式化器
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String format3 = atTime.format(dtf);
System.out.println(format3);//2018-11-25 10:25:00,完美解决
//将时分秒归零
LocalDateTime atStartOfDay = LocalDate.now().atStartOfDay();
String format4 = atStartOfDay.format(dtf);
System.out.println(format4);//2018-11-25 00:00:00
/*
* int compareTo(ChronoLocalDate other)和boolean equals(Object obj)
* 有同样的效果，都重写了父类的方法
* 其实equals 方法就是调用了compareTo方法
*/
if (LocalDate.now().equals(LocalDate.of(2018, 11, 25))) {
System.out.println(true);
}
if (LocalDate.now().compareTo(LocalDate.of(2018, 11, 25))==0) {
System.out.println(true);
}
/*
* is系列方法：
* boolean isAfter(ChronoLocalDate other)
* boolean isBefore(ChronoLocalDate other)
* boolean isEqual(ChronoLocalDate other)
* 和上面的compareTo和equals方法是统一性质
*/
//至此：大功告成，字字看来皆是血，几天辛苦不寻常
}
}