获取指定月份前的第一天和最后一天

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    public static Map<String,String> getMonthMap(int month){
        Map<String,String> monthMap = new HashMap<>();
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        // 获取前月的第一天
        Calendar cal_1 = Calendar.getInstance();// 获取当前日期
        cal_1.add(Calendar.MONTH, -month);
        cal_1.set(Calendar.DAY_OF_MONTH, 1);// 设置为1号,当前日期既为本月第一天
        String firstDay = format.format(cal_1.getTime());
        // 获取前月的最后一天
        Calendar cale = Calendar.getInstance();
        cale.add(Calendar.MONTH, -(month-1));
        cale.set(Calendar.DAY_OF_MONTH, 0);
        String lastDay = format.format(cale.getTime());
        monthMap.put("firstDay", firstDay);
        monthMap.put("lastDay", lastDay);
        return monthMap;
    }