关于Java类Calendar做统计时 获取日期的一些常见操作

 //通过调整日历，获得本天所属周的周一和周日
 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
 Calendar cal=new GregorianCalendar();
 cal.setFirstDayOfWeek(Calendar.MONDAY);
 cal.setTime(new Date());
 cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
 String startTime1 = sdf.format(cal.getTime());
 cal.set(Calendar.DATE, cal.get(cal.DATE) + 6);  
 String endTime1 = sdf.format(cal.getTime());
 date = startTime1+"~"+endTime1;

　　Calendar calendar = Calendar.getInstance();

calendar.setTime(startTime);//startTime当前查询周的周一（不一定是本周，也可以是指定查询某一天的周一） 
calendar.set(Calendar.DATE, calendar.get(calendar.DATE) -1); 
end2 = sdf.parse(sdf.format(calendar.getTime()));
calendar.set(Calendar.DATE, calendar.get(calendar.DATE) -6);
start2 = sdf.parse(sdf.format(calendar.getTime()));

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            //遍历日期来查询，保证一天一查，查询结果是对的
            Calendar c = Calendar.getInstance();
            c.setTime(startTime);
            Date time = sdf.parse(sdf.format(c.getTime()));
            while(time.getTime()<=endTime.getTime())
            {
                //不是今天
                if(time.getTime()!=sdf.parse(sdf.format(new Date())).getTime())
                {
                    SalesOrderStatDay dayObj = salesOrderStatDayDAO.getDataByDate(userId,time);
                    list.add(dayObj);
                }
                else
                {
                    //统计一下今天的报单数据，因为后台数据是使用quartz定时任务在零点才去统计当天数据，为了能看到当天数据 只能去实时查询
                    SalesOrderStatDay dayObj = getTodayData(userId);
                    list.add(dayObj);
                }
                c.add(Calendar.DATE, 1);
                time = sdf.parse(sdf.format(c.getTime()));//从周一加到周日
                
                
            }

sdf= new SimpleDateFormat("yyyy-MM");
            Calendar calendar = Calendar.getInstance();
            try {
                calendar.setTime(sdf.parse(month));
            } catch (ParseException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            calendar.set(calendar.MONTH, calendar.get(calendar.MONTH) -1);//进行减一操作，因为系统计算月份是从0开始
            date2 = sdf.format(calendar.getTime());

SimpleDateFormat sdf= new SimpleDateFormat("yyyy-MM");
            SimpleDateFormat sdflll= new SimpleDateFormat("yyyy-MM-dd");
            Date today = sdflll.parse(sdflll.format(new Date()));
            Calendar cal = Calendar.getInstance();
            cal.setTime(sdf.parse(date));
            //总天数
            int dayNum = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
            cal.set(Calendar.DAY_OF_MONTH,1);
            for(int i=1;i<=dayNum;i++)
            {
                Date time = sdflll.parse(sdflll.format(cal.getTime()));
                //不是今天
                if(cal.getTime()!=today.getTime())
                {
                    SalesOrderStatDay dayObj = salesOrderStatDayDAO.getDataByDate(userId,time);
                    list.add(dayObj);
                }
                else
                {
                    //统计一下今天的报单数据
                    SalesOrderStatDay dayObj = getTodayData(userId);
                    list.add(dayObj);
                }
                cal.add(Calendar.DATE, 1);//日期加一
                
            }