Java中的日期与时间获取与转换？

• JDK1.8 之前，使用 java.util.Calendar
• JDK1.8 提供了 java.time 包
• 还有第三方时间类库 Joda-Time 也可以

package constxiong.interview;

import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.MonthDay;
import java.time.Year;
import java.time.format.DateTimeFormatter;
import java.util.Calendar;
import java.util.Date;

/**
 * 测试时间和日期
 * @author ConstXiong
 * @date 2019-11-01 11:05:59
 */
public class TestDateAndTime {

    public static void main(String[] args) {
        //获取当前的年、月、日、时、分、秒、毫秒、纳秒
        //年
        System.out.println(Calendar.getInstance().get(Calendar.YEAR));
        //JDK 1.8 java.time 包
        System.out.println(Year.now());
        System.out.println(LocalDate.now().getYear());
        
        //月
        System.out.println(Calendar.getInstance().get(Calendar.MONTH)+1);
        //JDK 1.8 java.time 包
        System.out.println(MonthDay.now().getMonthValue());
        System.out.println(LocalDate.now().getMonthValue());
        
        //日
        System.out.println(Calendar.getInstance().get(Calendar.DAY_OF_MONTH));
        //JDK 1.8 java.time 包
        System.out.println(MonthDay.now().getDayOfMonth());
        System.out.println(LocalDate.now().getDayOfMonth());
        
        //时
        System.out.println(Calendar.getInstance().get(Calendar.HOUR_OF_DAY));
        //JDK 1.8 java.time 包
        System.out.println(LocalTime.now().getHour());
        
        //分
        System.out.println(Calendar.getInstance().get(Calendar.MINUTE));
        //JDK 1.8 java.time 包
        System.out.println(LocalTime.now().getMinute());
        
        //秒
        System.out.println(Calendar.getInstance().get(Calendar.SECOND));
        //JDK 1.8 java.time 包
        System.out.println(LocalTime.now().getSecond());
        
        //毫秒
        System.out.println(Calendar.getInstance().get(Calendar.MILLISECOND));
        
        //纳秒
        System.out.println(LocalTime.now().getNano());
        
        
        //当前时间毫秒数
        System.out.println(System.currentTimeMillis());
        System.out.println(Calendar.getInstance().getTimeInMillis());
        
        
        //某月最后一天
        //2018-05月最后一天,6月1号往前一天
        Calendar c = Calendar.getInstance();
        c.set(Calendar.YEAR, 2018);
        c.set(Calendar.MONTH, 5);
        c.add(Calendar.DAY_OF_MONTH, -1);
        System.out.println(c.get(Calendar.YEAR) + "-" + (c.get(Calendar.MONTH)+1) + "-" + c.get(Calendar.DAY_OF_MONTH));
        //JDK 1.8 java.time 包
        LocalDate date = LocalDate.of(2019, 6, 1).minusDays(1);
        System.out.println(date.getYear() + "-" + date.getMonthValue() + "-" + date.getDayOfMonth());
        
        
        //格式化日期
        System.out.println(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()));
        //JDK 1.8 java.time 包
        System.out.println(LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
    }
}

   

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