LocalDate的简单用法介绍

一、背景

Java8的特性已经不再是“新特性”，很多Java8的类也逐渐被更多的程序员在使用。

但是项目中的日期工具类，有一些还用的是Calandar类，非常不方便。

本文简单给出几个LocalDate的封装，展示一下基本用法。

大家可以多使用Java 8的时间相关类，功能更强大，代码更简洁。

二、上代码

Demo日期工具类

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.time.*;
import java.time.format.DateTimeFormatter;

import static java.time.temporal.TemporalAdjusters.firstDayOfMonth;

/**
 * @author 明明如月
 * @date 2018/11/14
 */
public class DateUtil {
    public static DateTimeFormatter defaultDateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");

    public static DateTimeFormatter simpleDateTimeFormatter = DateTimeFormatter.ofPattern("yyyyMMdd");

    public static DateTimeFormatter defaultFormatterWithTime = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

    /**
     * '前一天的日期
     */
    public static LocalDate lastDay(String date, DateTimeFormatter dateTimeFormatter) {
        LocalDate localDate = LocalDate.parse(date, dateTimeFormatter);
        return localDate.minusDays(1);
    }

    /**
     * 本周一的日期
     */
    public static LocalDate thisWeekFirstDay(String date, DateTimeFormatter dateTimeFormatter) {
        LocalDate localDate = LocalDate.parse(date, dateTimeFormatter);
        return localDate.with(DayOfWeek.MONDAY);
    }

    /**
     * 上周一
     */
    public static LocalDate lastWeekFirstDay(String date, DateTimeFormatter dateTimeFormatter) {
        LocalDate localDate = LocalDate.parse(date, dateTimeFormatter);
        return localDate.minusDays(7).with(DayOfWeek.MONDAY);
    }

    /**
     * 本月第一天
     */
    public static LocalDate thisMonthFirstDay(String date, DateTimeFormatter dateTimeFormatter) {
        LocalDate localDate = LocalDate.parse(date, dateTimeFormatter);
        return localDate.with(firstDayOfMonth());
    }

    /**
     * 上月第一天
     */
    public static LocalDate lastMonthFirstDay(String date, DateTimeFormatter dateTimeFormatter) {
        LocalDate localDate = LocalDate.parse(date, dateTimeFormatter);
        return localDate.minusMonths(1).with(firstDayOfMonth());
    }

    /**
     * 两个时间之间间隔了多少年
     */
    public static BigDecimal year(long low, long high) {
        Instant instant1 = Instant.ofEpochMilli(low);
        Instant instant2 = Instant.ofEpochMilli(high);

        LocalDate localDate1 = LocalDateTime.ofInstant(instant1, ZoneId.systemDefault()).toLocalDate();
        LocalDate localDate2 = LocalDateTime.ofInstant(instant2, ZoneId.systemDefault()).toLocalDate();
        Period period = Period.between(
                localDate1
                , localDate2
        );
        int years = period.getYears();
        int months = period.getMonths();
        BigDecimal monthToYear = new BigDecimal(months).divide(BigDecimal.valueOf(12), 2, RoundingMode.DOWN);
        return BigDecimal.valueOf(years).add(monthToYear);
    }

    /**
     * 是否是同一天
     */
    public static boolean isSameDateByUnixTime(long time1, long time2) {
        LocalDateTime dateTime1 = Instant.ofEpochMilli(time1).atZone(ZoneId.systemDefault()).toLocalDateTime();
        LocalDateTime dateTime2 = Instant.ofEpochMilli(time2).atZone(ZoneId.systemDefault()).toLocalDateTime();
        return dateTime1.toLocalDate().isEqual(dateTime2.toLocalDate());
    }

}

测试类

import com.chujianyun.common.java8.date.DateUtil;
import org.junit.Assert;
import org.junit.jupiter.api.Test;

import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.text.ParseException;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

class DateUtilTest {

    private String today = "2019-05-10";

    private DateTimeFormatter dateTimeFormatter = DateUtil.defaultDateTimeFormatter;

    @Test
    void lastDay() {
        LocalDate localDate = DateUtil.lastDay(today, dateTimeFormatter);
        Assert.assertEquals("2019-05-09", dateTimeFormatter.format(localDate));
    }

    @Test
    void thisWeekFirstDay() {
        LocalDate localDate = DateUtil.thisWeekFirstDay(today, dateTimeFormatter);
        Assert.assertEquals("2019-05-06", dateTimeFormatter.format(localDate));
    }

    @Test
    void lastWeekFirstDay() {
        LocalDate localDate = DateUtil.lastWeekFirstDay(today, dateTimeFormatter);
        Assert.assertEquals("2019-04-29", dateTimeFormatter.format(localDate));
    }

    @Test
    void thisMonthFirstDay() {
        LocalDate localDate = DateUtil.thisMonthFirstDay(today, dateTimeFormatter);
        Assert.assertEquals("2019-05-01", dateTimeFormatter.format(localDate));
    }

    @Test
    void lastMonthFirstDay() {
        LocalDate localDate = DateUtil.lastMonthFirstDay(today, dateTimeFormatter);
        Assert.assertEquals("2019-04-01", dateTimeFormatter.format(localDate));
    }

    @Test
    public void test() throws ParseException {
        // 2018-01-01 --> 1514736000000
        // 2018-01-01 --> 1546272000000

        BigDecimal year = DateUtil.year(1514736000000L, 1546272000000L);
        BigDecimal expect = new BigDecimal(1);
        BigDecimal bigDecimal = expect.setScale(2, BigDecimal.ROUND_HALF_UP);
        Assert.assertEquals(bigDecimal, year);
    }

    @Test
    public void isSameDay() {
        boolean sameDateByUnixTime = DateUtil.isSameDateByUnixTime(1514779260000L, 1514818860000L);
        Assert.assertTrue(sameDateByUnixTime);
    }
}

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