Java获取本月、本周的第一天&最后一天

/**
     * 获取本月第一天
     * @return String
     **/
    public static String getMonthStart() {
        Calendar cal = Calendar.getInstance();
        cal.add(Calendar.MONTH, 0);
        cal.set(Calendar.DAY_OF_MONTH, 1);
        Date time = cal.getTime();
        return new SimpleDateFormat("yyyy-MM-dd").format(time) + " 00:00:00";
    }

    /**
     * 获取本月最后一天
     * @return String
     **/
    public static String getMonthEnd() {
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DAY_OF_MONTH));
        Date time = cal.getTime();
        return new SimpleDateFormat("yyyy-MM-dd").format(time) + " 23:59:59";
    }

    /**
     * 获取本周的第一天
     * @return String
     **/
    public static String getWeekStart() {
        Calendar cal = Calendar.getInstance();
        cal.add(Calendar.WEEK_OF_MONTH, 0);
        cal.set(Calendar.DAY_OF_WEEK, 2);
        Date time = cal.getTime();
        return new SimpleDateFormat("yyyy-MM-dd").format(time) + " 00:00:00";
    }

    /**
     * 获取本周的最后一天
     * @return String
     **/
    public static String getWeekEnd() {
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.DAY_OF_WEEK, cal.getActualMaximum(Calendar.DAY_OF_WEEK));
        cal.add(Calendar.DAY_OF_WEEK, 1);
        Date time = cal.getTime();
        return new SimpleDateFormat("yyyy-MM-dd").format(time) + " 23:59:59";
    }