根据给的年月,获取当月第一天和最后一天

/**
	 * 根据给的时间获取此月的最后一天
	 * 传入参数为String,可传入:1、"201807";2、"2018-07-01"
	 * @param date
	 * 			账期
	 * @return String
	 * 			当月的最后一天
	 */
	public static String getLastDayByMonth(String date) {
		if (date.contains("-")) {
			date = date.replaceAll("-", "");
		} else if (date.length() < 6 || date.length() > 10) {
			System.out.println("日期错误!");
		}
		int year = Integer.parseInt(date.substring(0, 4));
		int month = Integer.parseInt(date.substring(4, 6));
		Calendar cal = Calendar.getInstance();
		cal.set(Calendar.YEAR, year);
		cal.set(Calendar.MONTH, month - 1);
		cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DAY_OF_MONTH));
		return new SimpleDateFormat("yyyy-MM-dd ").format(cal.getTime());
	}
	/**
	 * 根据给的时间获取此月的第一天
	 * 传入参数为String,可传入:1、"201807";2、"2018-07-01"
	 * @param date
	 * 			账期
	 * @return String
	 * 			当月的第一天
	 */
	public static String getFirstDayByMonth(String date) {
		if (date.contains("-")) {
			date = date.replaceAll("-", "");
		} else if (date.length() < 6 || date.length() > 10) {
			System.out.println("日期错误!");
		}
		int year = Integer.parseInt(date.substring(0, 4));
		int month = Integer.parseInt(date.substring(4, 6));
		Calendar cal = Calendar.getInstance();
		cal.set(Calendar.YEAR, year);
		cal.set(Calendar.MONTH, month - 1);
		cal.set(Calendar.DAY_OF_MONTH, cal.getActualMinimum(Calendar.DATE));
		return new SimpleDateFormat("yyyy-MM-dd ").format(cal.getTime());
	}