java日期获取

  // 获取今年第一天
	Calendar currCal=Calendar.getInstance();
	Calendar calendar = Calendar.getInstance();
	calendar.clear();
	calendar.set(Calendar.YEAR,currCal.get(Calendar.YEAR));
	Date time = calendar.getTime();
	SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
	String firstday =  format.format(time);
  //获取当月第一天
	SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
	String firstday;
	Calendar cale = Calendar.getInstance();
	cale.add(Calendar.MONTH, 0);
	cale.set(Calendar.DAY_OF_MONTH, 1);
	String firstday = format.format(cale.getTime());
  //获取当年最后一天
  	Calendar currCal= Calendar.getInstance();
	Calendar calendar = Calendar.getInstance();
	calendar.clear();
	calendar.set(Calendar.YEAR,currCal.get(Calendar.YEAR));
	calendar.roll(Calendar.DAY_OF_YEAR,-1);
	Date time = calendar.getTime();
	SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");  
	String firstday =  format.format(time);

搜索关键字：
python get every first day of month
参考解答：
方法一：
>>> import calendar
>>> calendar.monthrange(2002,1)
(1, 31)
>>> calendar.monthrange(2008,2)
(4, 29)
>>> calendar.monthrange(2100,2)
(0, 28)
>>> calendar.monthrange(2016, 2)[1]
方法二：
import datetime
for x in xrange(1, 13):
dt_start = (datetime.datetime(2016, x, 1)).strftime("%Y%m%d")
if 12 == x:
dt_end = (datetime.datetime(2016, 12, 31)).strftime("%Y%m%d")
else:
dt_end = (datetime.datetime(2016, x+1, 1) - datetime.timedelta(days = 1)).strftime("%Y%m%d")
print dt_start, dt_end
参考链接：
http://stackoverflow.com/questions/42950/get-last-day-of-the-month-in-python
https://docs.python.org/2/library/calendar.html
https://docs.python.org/2/library/datetime.html
http://stackoverflow.com/questions/22696662/python-list-of-first-day-of-month-for-given-period
总结
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1、写一个方法，设置两个时间段

protected bool getTimeSpan(string timeStr)
        {
            //判断当前时间是否在工作时间段内
            string _strWorkingDayAM = "08:30";//工作时间上午08:30
            string _strWorkingDayPM = "17:00";
            TimeSpan dspWorkingDayAM = DateTime.Parse(_strWorkingDayAM).TimeOfDay;
            TimeSpan dspWorkingDayPM = DateTime.Parse(_strWorkingDayPM).TimeOfDay;

            //string time1 = "2017-2-17 8:10:00";
            DateTime t1 = Convert.ToDateTime(timeStr);

            TimeSpan dspNow = t1.TimeOfDay;
            if (dspNow > dspWorkingDayAM && dspNow < dspWorkingDayPM)
            {
                return true;
            }
            return false;
        }

2、定义一个变量

protected string getResult = string.Empty;

3、在button单击事件中调用

 private void button4_Click(object sender, EventArgs e)
        {
            string time1 = "19:45:00";    //设置一个时间，下边调用方法返回true就是在工作时间内
            //DateTime t1 = Convert.ToDateTime(time1);
            bool resultBool = getTimeSpan(time1);
            getResult = Convert.ToString(resultBool);
            MessageBox.Show(getResult);
        }

4、效果（步骤3中设置的时间如果在步骤1设置的时间段中返回true否则相反）



 

5.判断时间是否是今天

 string start = "2020-04-23 17:00:00";
            DateTime now = DateTime.Now;
            DateTime today2 = new DateTime(now.Year, now.Month, now.Day);//当天的零时零分
            if (DateTime.Parse(start) > today2)
            {
                MessageBox.Show("yes");
            }
            else
            {
                MessageBox.Show("no");

            }

6.获取今年第一天、最后一天

/// <summary>  
        /// 获取本年年初, 本年度第一天
        /// </summary>  
        /// <param name="dateTime">当前时间 DateTime.Now or DateTime.UtcNow</param>  
        /// <returns>后面的具体时、分、秒和传入值相等</returns>  
        public static DateTime GetYearFirstDate(DateTime dateTime)
        {
            // 本年年初
            return dateTime.AddMonths(1 - dateTime.Month).AddDays(1 - dateTime.Day);
        }
 
        /// <summary>
        /// 获取本年年末, 本年度最后一天
        /// </summary>
        /// <param name="dateTime">当前时间 DateTime.Now or DateTime.UtcNow</param>  
        /// <returns>后面的具体时、分、秒和传入值相等</returns>
        public static DateTime GetYearLastDate(DateTime dateTime)
        {
            // 本年年末
            return GetYearFirstDate(dateTime).AddYears(1).AddDays(-1);
        }

7.数字字符串转换为日期类型

string dateString = "20110526";

DateTime dt = DateTime.ParseExact(dateString, "yyyyMMdd", System.Globalization.CultureInfo.CurrentCulture);

或者

DateTime dt = DateTime.ParseExact(dateString, "yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture);

 

#coding=utf-8
import datetime
from datetime import timedelta
now = datetime.datetime.now()
#今天
today = now
#昨天
yesterday = now - timedelta(days=1)
#明天
tomorrow = now + timedelta(days=1)
#当前季度
now_quarter = now.month / 3 if now.month % 3 == 0 else now.month / 3 + 1
#本周第一天和最后一天
this_week_start = now - timedelta(days=now.weekday())
this_week_end = now + timedelta(days=6-now.weekday())
#上周第一天和最后一天
last_week_start = now - timedelta(days=now.weekday()+7)
last_week_end = now - timedelta(days=now.weekday()+1)
#本月第一天和最后一天
this_month_start = datetime.datetime(now.year, now.month, 1)
this_month_end = datetime.datetime(now.year, now.month + 1, 1) - timedelta(days=1)
#上月第一天和最后一天
last_month_end = this_month_start - timedelta(days=1)
last_month_start = datetime.datetime(last_month_end.year, last_month_end.month, 1)
#本季第一天和最后一天
month = (now.month - 1) - (now.month - 1) % 3 + 1
this_quarter_start = datetime.datetime(now.year, month, 1)
this_quarter_end = datetime.datetime(now.year, month + 3, 1) - timedelta(days=1)
#上季第一天和最后一天
last_quarter_end = this_quarter_start - timedelta(days=1)
last_quarter_start = datetime.datetime(last_quarter_end.year, last_quarter_end.month - 2, 1)
#本年第一天和最后一天
this_year_start = datetime.datetime(now.year, 1, 1)
this_year_end = datetime.datetime(now.year + 1, 1, 1) - timedelta(days=1)
#去年第一天和最后一天
last_year_end = this_year_start - timedelta(days=1)
last_year_start = datetime.datetime(last_year_end.year, 1, 1)