java----获取当前月份的第一天、当前天、最后一天

		SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
		//获取当前日期
		Calendar ca=Calendar.getInstance();
		ca.add(Calendar.MONTH, 0);
		ca.set(Calendar.DAY_OF_MONTH,1);
        ca.set(Calendar.DAY_OF_MONTH, ca.getActualMaximum(Calendar.DAY_OF_MONTH)); 
       
		String start = format.format(ca.getTime());
        String today = format.format(new Date());               
        String last = format.format(ca.getTime());