JDK日期时间

package com.xt.java2;

import org.junit.Test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

import static java.util.Calendar.DAY_OF_MONTH;


public class DateTimeTest {
    
    @Test
    public void testSimpleDateFormat() throws ParseException {
        //实例化,使用默认的构造器
        SimpleDateFormat sdf = new SimpleDateFormat();

        //格式化：日期-->字符串
        Date date = new Date();
        System.out.println(date);
        String s = sdf.format(date);
        System.out.println(s);
        //解析：字符串-->日期
        String str="2022/4/19 上午10:22";
        Date date1=sdf.parse(str);
        System.out.println(date1);
    }
    @Test
    public void testSimpleDateFormat1() throws ParseException {
        //按照指定的方式格式化和解析：调用带参的构造器
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
        //格式化：日期-->字符串
        Date date = new Date();
        String str = sdf.format(date);
        System.out.println(str+"格式化");
        //解析：字符串-->日期 要求：字符串必须是SimpleDateFormat识别的格式（通过构造器参数体现）
        Date date1 = sdf.parse("2022-04-19 10:42:11");
        System.out.println(date1+"解析");
    }
    
    @Test
    public void testExer() throws ParseException {
        String birth="1997-06-20";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        Date date = sdf.parse(birth);
        java.sql.Date date1=new java.sql.Date(date.getTime());
        System.out.println(date1);
    }
    
    @Test
    public void testCalendar(){
        //1.实例化
        //方式1：创建其子类（GregorianCalendar）的对象
        //方式2：调用它的静态方法
        Calendar calendar=Calendar.getInstance();
        System.out.println(calendar);

        //2.常用方法
        //get()
        int days = calendar.get(DAY_OF_MONTH);
        System.out.println(days);
        days = calendar.get(Calendar.DAY_OF_YEAR);
        System.out.println(days);
        //set()
        //Calendar可变性
        calendar.set(DAY_OF_MONTH,28);
        days=calendar.get(DAY_OF_MONTH);
        System.out.println(days);
        //add()
        calendar.add(DAY_OF_MONTH,-7);
        days=calendar.get(DAY_OF_MONTH);
        System.out.println(days);
        //getTime() -- 日历类-->Date
        Date date = calendar.getTime();
        System.out.println(date);
        //setTime() -- Date-->日历类
        Date date1=new Date();
        calendar.setTime(date1);
        days=calendar.get(DAY_OF_MONTH);
        System.out.println(days);
    }

}

package com.xt.java2;

import org.junit.Test;

import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.format.FormatStyle;
import java.time.temporal.TemporalAccessor;
import java.util.Date;


public class JDK8DateTimeTest {
    @Test
    public void testDate(){
        //偏移量
        Date date=new Date(2022-1900,4-1,28);
        System.out.println(date);//Thu Apr 28 00:00:00 CST 2022
    }
    
    @Test
    public void test1(){
        //获取当前的日期、时间、日期+时间
        LocalTime localTime = LocalTime.now();
        LocalDate localDate = LocalDate.now();
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println(localTime);
        System.out.println(localDate);
        System.out.println(localDateTime);

        //of():设置指定的年、月、日、时、分、秒是没有偏移量的
        LocalDateTime localDateTime1 = localDateTime.of(2022, 4, 28, 19, 00, 43);
        System.out.println(localDateTime1);

        //getXxx()获取相关的属性
        System.out.println(localDateTime.getDayOfMonth());
        System.out.println(localDateTime.getDayOfWeek());
        System.out.println(localDateTime.getMonth());
        System.out.println(localDateTime.getYear());

        //体现以上3个类的不可变性
        //withXxx():设置相关属性
        LocalDate localDate1 = localDate.withDayOfMonth(22);
        System.out.println(localDate);
        System.out.println(localDate1);
        LocalDateTime localDateTime2 = localDateTime.withHour(5);
        System.out.println(localDateTime);
        System.out.println(localDateTime2);
        //不可变性
        LocalDateTime plusMonths = localDateTime.plusMonths(3);
        System.out.println(plusMonths);
        LocalDateTime minusDays = localDateTime.minusDays(12);
        System.out.println(minusDays);
    }
    
    @Test
    public void test2(){
        //now获取本初子午线对应的标准时间
        Instant instant = Instant.now();
        System.out.println(instant);
        //添加时间的偏移量
        OffsetDateTime offsetDateTime = instant.atOffset(ZoneOffset.ofHours(8));
        System.out.println(offsetDateTime);
        //toEpochMilli()：获取自1970年1月1日0时0分0秒对应的毫秒数 -->Date类的getTime()
        long epochMilli = instant.toEpochMilli();
        System.out.println(epochMilli);

        //ofEpochMilli():通过给定的毫秒数，获取Instant实例  -->Date(Long millis)
        Instant ofEpochMilli = Instant.ofEpochMilli(1650593009205L);
        System.out.println(ofEpochMilli);
    }
    
    @Test
    public void test3(){
        //方式一：预定义的标准格式
        DateTimeFormatter formatter=DateTimeFormatter.ISO_LOCAL_DATE_TIME;
        //格式化：日期-->字符串
        LocalDateTime localDateTime=LocalDateTime.now();
        String format = formatter.format(localDateTime);
        System.out.println(localDateTime);
        System.out.println(format);

        //解析：字符串-->日期
        TemporalAccessor parse = formatter.parse("2022-04-22T11:22:15.2600813");
        System.out.println(parse);

        //方式二：本地化相关的格式:ofLocalizedDateTime
        DateTimeFormatter formatter1 = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT);
        String str = formatter1.format(localDateTime);
        System.out.println(str);  //2022/4/22 上午11:31
        //会报异常
//        DateTimeFormatter formatter2 = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG);
//        String str2 = formatter2.format(localDateTime);
//        System.out.println(str2);  //2022/4/22 上午11:31

        //（重点）方式三：自定义的格式,如:ofPattern("yyyy-MM-dd hh:mm:ss")
        DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
        //格式化
        String format1 = formatter2.format(LocalDateTime.now());
        System.out.println(format1);
        //解析
        TemporalAccessor accessor = formatter2.parse("2022-04-22 04:13:28");
        System.out.println(accessor);

    }
}