获取某一月份的第一天和最后一天（主意2月的平年瑞年天数）

获取第一天

public static String getFirstDayOfMonth(Date date) {
        Calendar cal = Calendar.getInstance();
        cal.setTime(date);
        // 设置月份
        //cal.set(Calendar.MONTH, month - 1);
        // 获取某月最小天数
        int firstDay = cal.getActualMinimum(Calendar.DAY_OF_MONTH);
        // 设置日历中月份的最小天数
        cal.set(Calendar.DAY_OF_MONTH, firstDay);
        // 格式化日期
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        String firstDayOfMonth = sdf.format(cal.getTime())+" 00:00:00";
        return firstDayOfMonth;
    }

获取最后一天

public static String getLastDayOfMonth(Date date) {
	    Calendar cal = Calendar.getInstance();
	    cal.setTime(date);
	    
	    int month = cal.get(Calendar.MONTH);
	    
	    // 获取某月最大天数
	    int lastDay=0;
	   //2月的平年瑞年天数
	   if(month==2) {
	     lastDay = cal.getLeastMaximum(Calendar.DAY_OF_MONTH);
	   }else {
	      lastDay = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
	   }
	    // 设置日历中月份的最大天数
	     cal.set(Calendar.DAY_OF_MONTH, lastDay);
	    // 格式化日期
	    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
	    String lastDayOfMonth = sdf.format(cal.getTime())+" 23:59:59";
	    return lastDayOfMonth;
	 }

调用

	public void mytest16() throws ParseException {
		
		String mytime = "2004-02";
		DateFormat dateFormat = new SimpleDateFormat("yyyy-MM");
		Date myDate = dateFormat.parse(mytime);
		String firstDayOfMonth = getFirstDayOfMonth(myDate);
		String lastDayOfMonth = getLastDayOfMonth(myDate);
		System.out.println(firstDayOfMonth);
		System.out.println(lastDayOfMonth);
		
	}

结果：
2004-02-01 00:00:00
2004-02-29 23:59:59