简单但实用的日期工具类

java8已经出来那么长时间了，不会还有人还在用第三方日期工具类吧

使用JDK提供的LocalDateTime和Duration，了解日期的构造、计算、比较、转换等等各种姿势，足以满足日常中的各种需求，除非你的产品又提五彩斑斓的黑...

但很多同学提出：现有项目用的Date、时间戳、各种格式的日期字符串，要切换到新API成本太高了。

其实统一梳理下转换工具，也挺简单：

import java.time.Duration;
import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;
import java.util.Date;
import java.util.Objects;
import java.util.function.Function;

public final class DateTimes {
    private static final DateTimeFormatter DEFAULT_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    private LocalDateTime localDateTime;

    private DateTimes(LocalDateTime localDateTime) {
        this.localDateTime = localDateTime;
    }

    public static DateTimes now() {
        return new DateTimes(LocalDateTime.now());
    }

    public static DateTimes of(long epochMilli) {
        return new DateTimes(LocalDateTime.ofInstant(Instant.ofEpochMilli(epochMilli), ZoneOffset.systemDefault()));
    }

    public static DateTimes of(Date date) {
        return new DateTimes(date.toInstant().atZone(ZoneOffset.systemDefault()).toLocalDateTime());
    }

    public static DateTimes of(LocalDateTime localDateTime) {
        return new DateTimes(localDateTime);
    }

    public static DateTimes of(String text) {
        return new DateTimes(LocalDateTime.parse(text, DEFAULT_FORMATTER));
    }

    public static DateTimes of(String text, DateTimeFormatter formatter) {
        return new DateTimes(LocalDateTime.parse(text, formatter));
    }

    public DateTimes then(Function<LocalDateTime, LocalDateTime> then) {
        this.localDateTime = (LocalDateTime)then.apply(this.localDateTime);
        return this;
    }

    public long toMills() {
        return this.localDateTime.atZone(ZoneOffset.systemDefault()).toInstant().toEpochMilli();
    }

    public String format() {
        return this.localDateTime.format(DEFAULT_FORMATTER);
    }

    public String format(DateTimeFormatter formatter) {
        return this.localDateTime.format(formatter);
    }

    public LocalDateTime toLocalDateTime() {
        return this.localDateTime;
    }

    public boolean equals(Object o) {
        if (this == o) {
            return true;
        } else if (o != null && this.getClass() == o.getClass()) {
            DateTimes dateTimes = (DateTimes)o;
            return Objects.equals(this.localDateTime, dateTimes.localDateTime);
        } else {
            return false;
        }
    }

    public int hashCode() {
        return Objects.hash(new Object[]{this.localDateTime});
    }

    public String toString() {
        return this.format();
    }    
}

怎么使用呢？

public static void main(String[] args) {
    Date date = new Date();
    System.out.println(DateTimes.of(date).equals(DateTimes.of(date.getTime())));
    System.out.println(DateTimes.now().then((e) -> {
        return e.plusDays(1L).plusSeconds(1L).plusHours(1L);
    }).format());
    
    LocalDateTime now = LocalDateTime.now();
    LocalDateTime tomorrow = LocalDate.now().plusDays(1L).atStartOfDay();
    LocalDateTime today = LocalDate.now().atStartOfDay();
    System.out.println(Duration.between(now, tomorrow).getSeconds());
    System.out.println(Duration.between(now, today).getSeconds());
    System.out.println(Duration.between(now, tomorrow).getSeconds() - Duration.between(now, today).getSeconds() == Duration.ofDays(1L).getSeconds());
}

万里长征第一步, 前面是诗与远方，快来试试吧。