Calendar calendar = new GregorianCalendar();  
				    calendar.add(Calendar.DAY_OF_MONTH,-1);  
				  
				    //一天的开始时间 yyyy:MM:dd 00:00:00  
				    calendar.set(Calendar.HOUR_OF_DAY,0);  
				    calendar.set(Calendar.MINUTE,0);  
				    calendar.set(Calendar.SECOND,0);  
				    calendar.set(Calendar.MILLISECOND,0);  
				    Date dayStart = calendar.getTime();  
				    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  
				    String startStr = simpleDateFormat.format(dayStart) ;