java中Date和Timestamp类型的相互转换方式

import java.sql.Timestamp;
import java.util.Date;
public class Test{
    public static void main(String[] args){
        //Date 转 Timestamp
        Date d = new Date(); //系统时间
        System.out.println(d.toString()); //Wed Dec 14 17:47:51 CST 2022 （CST表示北京时间）
        long time = d.getTime();
        System.out.println(time); //1671011534602,这其实是以毫秒为单位的
        Timestamp timestamp = new Timestamp(time);
        System.out.println(timestamp.toString()); //2022-12-14 17:47:51.531  （构造的时间戳有毫秒）
        //Timestamp 转 Date
        Timestamp timestamp2 = new Timestamp(1671011899628l); //是2022-12-14 17:58:19.628的时间数值
        System.out.println(timestamp2.toString()); //2022-12-14 17:58:19.628
        long time2 = timestamp2.getTime();
        Date date2 = new Date(time2);
        System.out.println(date2.toString()); //Wed Dec 14 17:58:19 CST 2022 （Date类型没有毫秒）
    }
}

@Test
    public void testStringToDate() throws ParseException {
        String dateStr = "2021-12-10 11:11:11";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        //java.util包下的Date类;
        Date date = sdf.parse(dateStr);
        System.out.println(date.toString());
        //Fri Dec 10 11:11:11 CST 2021
    }

    @Test
    public void testDateToString(){
        Date date = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String dateStr = sdf.format(date);
        System.out.println(dateStr);
//        2021-12-10 10:22:31
    }

@Test
    public void testDateToTimeStamp(){
        Date date = new Date();
        Timestamp timestamp = new Timestamp(date.getTime());
        System.out.println(timestamp);
        //        2021-12-10 10:29:25.978
    }

    @Test
    public void testTimestampToDate(){
        Timestamp timestamp = new Timestamp(System.currentTimeMillis());
        Date date = new Date(timestamp.getTime());
        System.out.println(date);
//        Fri Dec 10 10:30:16 CST 2021
    }

    @Test
    public void testStringToTimestamp(){
        String dateStr = "2021-12-10 11:11:11";
        Timestamp timestamp = Timestamp.valueOf(dateStr);
        System.out.println(timestamp);
//        2021-12-10 11:11:11.0
    }

    @Test
    public void testTimestampToString(){
        Timestamp timestamp = new Timestamp(System.currentTimeMillis());
        SimpleDateFormat sdf = new SimpleDateFormat();
        String s = sdf.format(timestamp);
        System.out.println(s);
//        21-12-10 上午10:27
    }

   @Test
    public void testDateToCalendar(){
        Date date = new Date();
        Calendar instance = Calendar.getInstance();
        instance.setTime(date);
        System.out.println(instance.getTime());
//        Fri Dec 10 10:36:39 CST 2021
    }

    @Test
    public void testCalendarToDate(){
        Calendar instance = Calendar.getInstance();
        Date time = instance.getTime();
        System.out.println(time);
//        Fri Dec 10 10:56:30 CST 2021
    }