Java LocalDate/Date input and output example

UtilityTest.java

package app.ruyut.ruyutdemo;

import org.junit.jupiter.api.Test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.util.Date;
import java.util.Locale;

public class UtilityTest {

    @Test
    public void localDateTest() {

        // 將輸入的日期字串轉換為 LocalDate物件
        String inputDateString = "20220101";
        LocalDate localDate = LocalDate.parse(inputDateString, DateTimeFormatter.ofPattern("yyyyMMdd"));

        // 將 LocalDate物件 輸出為日期字串
        String localDateString = DateTimeFormatter.ofPattern("yyyy/MM/dd").format(localDate);
        System.out.println(localDateString); //2022/01/01

        // 輸出星期
        String weekString = DateTimeFormatter.ofPattern("EEEE", Locale.TAIWAN).format(localDate);
        System.out.println(weekString); // 星期六

        // 轉 Date
        Date date = Date.from(localDate.atStartOfDay(ZoneId.systemDefault()).toInstant());
        System.out.println(date); // Sat Jan 01 00:00:00 CST 2022
    }

    @Test
    public void dateTest() throws ParseException {

        // 將輸入的日期字串轉換為 Date物件
        String inputDateString = "2022/01/01 08:30";
        SimpleDateFormat inputSimpleDateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm");
        Date date = inputSimpleDateFormat.parse(inputDateString);

        // 將 Date物件 輸出為日期字串
        SimpleDateFormat outputSimpleDateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss.SSS");
        System.out.println(outputSimpleDateFormat.format(date)); // 2022/01/01 08:30:00.000

        // 輸出星期
        SimpleDateFormat outputWeekSimpleDateFormat = new SimpleDateFormat("EEEE", Locale.TAIWAN);
        System.out.println(outputWeekSimpleDateFormat.format(date)); // 星期六
        System.out.println(outputWeekSimpleDateFormat.format(date).substring(2)); // 六

        // 轉 LocalDate
        LocalDate localDate = date.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();
        System.out.println(localDate); // 2022-01-01
    }
}