获取本月的第一天和最后一天

	@Test
	public void test(){
		Date someDate = new Date();
		Calendar   ca   =   Calendar.getInstance();
		ca.setTime(someDate);                            //  someDate 为你要获取的那个月的时间
		ca.set(Calendar.DAY_OF_MONTH,   1);
		//第一天
		Date   firstDate   =   ca.getTime();
		
		System.out.println(firstDate.toLocaleString());
		
		ca.add(Calendar.MONTH,   1);
		ca.add(Calendar.DAY_OF_MONTH,   -1);
		//最后一天
		Date   lastDate   =   ca.getTime();
		
		System.out.println(lastDate.toLocaleString());
	}