[Java知识库]java获取时间（今天，昨天，上周第一天，本周第一天，本周最后一天）

1、获取当前时间（年月日时分秒）

        Date date = new Date();//获得系统时间.
        SimpleDateFormat sdf = new SimpleDateFormat(" yyyy-MM-dd HH:mm:ss");
        String nowTime = sdf.format(date);
        Date time = sdf.parse(nowTime);

?2、获取昨天时间（年月日时分秒）

        Date dNow = new Date();   //当前时间
        Date dBefore = new Date();
        Calendar calendar = Calendar.getInstance(); //得到日历
        calendar.setTime(dNow);//把当前时间赋给日历
        calendar.add(Calendar.DATE, -1);  //设置为前一天，一个月也是这么设置
        dBefore = calendar.getTime();   //设置为前一天时间
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); //设置时间格式
        String defaultStartDate = sdf.format(dBefore);    //格式化一天前
        System.out.println("查询时间" + defaultStartDate);

3、获取今天凌晨

public static Date getTimesmorning() {
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.HOUR_OF_DAY, 0);
        cal.set(Calendar.SECOND, 0);
        cal.set(Calendar.MINUTE, 0);
        cal.set(Calendar.MILLISECOND, 0);
        return cal.getTime();
    }

?4、获取第二天凌晨

 public static Date getTimesnight() {
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.HOUR_OF_DAY, 24);
        cal.set(Calendar.SECOND, 0);
        cal.set(Calendar.MINUTE, 0);
        cal.set(Calendar.MILLISECOND, 0);
        return cal.getTime();
    }

5、本周第一天（本周开始第一天）

 public static Date getWeekStartDate(){
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
        cal.set(Calendar.HOUR_OF_DAY, 0);
        cal.set(Calendar.MINUTE, 0);
        cal.set(Calendar.SECOND, 0);
        Date date = cal.getTime();
        return date;
    }

6、本周最后一天

public static Date getTimesmorning() {
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.HOUR_OF_DAY, 0);
        cal.set(Calendar.SECOND, 0);
        cal.set(Calendar.MINUTE, 0);
        cal.set(Calendar.MILLISECOND, 0);
        return cal.getTime();
    }

7、上周第一天

public static Date getSunday() {
        Calendar cal = Calendar.getInstance();
        //将每周第一天设为星期一，默认是星期天
        cal.setFirstDayOfWeek(Calendar.MONDAY);
        cal.add(Calendar.DATE, -1*7);
        cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);

        cal.set(Calendar.HOUR_OF_DAY, 0);
        cal.set(Calendar.MINUTE, 0);
        cal.set(Calendar.SECOND, 0);
        cal.set(Calendar.MILLISECOND, 0);
        return cal.getTime();
    }

8、本月第一天

public static Date getTimesMonthmorning() {
        Calendar cal = Calendar.getInstance();
        cal.set(cal.get(Calendar.YEAR), cal.get(Calendar.MONDAY), cal.get(Calendar.DAY_OF_MONTH), 0, 0, 0);
        cal.set(Calendar.DAY_OF_MONTH, cal.getActualMinimum(Calendar.DAY_OF_MONTH));
        return cal.getTime();
    }