根据账单日获取任何账期

PaymentDaysTest.java

/**
 * Java语法不允许数组索引值为负值或超出数组长度（含），该函数去除这一限制。
 * <br/>
 * 规则：<br/>
 * <code>
 * array=[1,2,3,4,5] <br/>
 * <p>
 * array[-1]=5 <br/>
 * array[-2]=4 <br/>
 * array[-3]=3 <br/>
 * array[-4]=2 <br/>
 * array[-5]=1 <br/>
 * array[-6]=5 <br/>
 * <p>
 * array[5]=1  <br/>
 * array[6]=2  <br/>
 * array[7]=3  <br/>
 * array[8]=4  <br/>
 * array[9]=5  <br/>
 * </code>
 *
 * @param array 数组
 * @param index 索引值
 * @return
 */
int anyIndexOf(int[] array, int index) {
    int _index = index > 0 ? index % array.length : (array.length + index) % array.length;
    return array[Math.abs(_index)];
}

/**
 * @param billDays  账单日
 * @param nextCount 要获取当前账期后的第几个账期。负值：前推账期；正值：后推账期
 * @return
 */
public PaymentDays nextPaymentDays(int[] billDays, int nextCount) {
    Arrays.sort(billDays); // 由小到大将账单日排序
    Calendar calendar = Calendar.getInstance(); // 日历系统
    int today = calendar.get(Calendar.DAY_OF_MONTH); // 今天是本月的第几天
    int paymentDaysDayLen = billDays.length; // 总共有多少个账单日
    PaymentDays thisPaymentDays = null; // 本账期
    PaymentDays nextPaymentDays = null; // 推nextCount个账期后的账期
    int thisPaymentDaysBeginBillIndex = 0; // 本账期 开始日期 是账单日中的哪一日
    int thisPaymentDaysEndBillIndex = 0; // 本账期 结束日期 是账单日中的哪一日
    /*
    设账单日为每月的5号、15号、25号，则 billDays=[5,15,25]
    若today<5，则
        thisPaymentDaysBeginBillIndex=-1 billDays[thisPaymentDaysBeginBillIndex]=25
        thisPaymentDaysEndBillIndex=0 billDays[thisPaymentDaysEndBillIndex]=5
    若today<15，则
        thisPaymentDaysBeginBillIndex=0 billDays[thisPaymentDaysBeginBillIndex]=5
        thisPaymentDaysEndBillIndex=1 billDays[thisPaymentDaysEndBillIndex]=15
    若today<25，则
        thisPaymentDaysBeginBillIndex=1 billDays[thisPaymentDaysBeginBillIndex]=15
        thisPaymentDaysEndBillIndex=2 billDays[thisPaymentDaysEndBillIndex]=25
     */
    for (int i = 0; i <= paymentDaysDayLen; i++) {
        if (today < anyIndexOf(billDays, i)) {
            thisPaymentDays = new PaymentDays();
            thisPaymentDaysBeginBillIndex = i - 1;
            calendar.set(Calendar.DAY_OF_MONTH, anyIndexOf(billDays, thisPaymentDaysBeginBillIndex));
            if (thisPaymentDaysBeginBillIndex < 0) {
                calendar.add(Calendar.MONTH, -1);
            }
            thisPaymentDays.setBegin(calendar.getTime());
            calendar.setTimeInMillis(System.currentTimeMillis());
            thisPaymentDaysEndBillIndex = i;
            calendar.set(Calendar.DAY_OF_MONTH, anyIndexOf(billDays, thisPaymentDaysEndBillIndex));
            if (i == paymentDaysDayLen) {
                calendar.add(Calendar.MONTH, 1);
            }
            thisPaymentDays.setEnd(calendar.getTime());
            break;
        }
    }
    /*
    若today>=25，则
        thisPaymentDaysBeginBillIndex=-1 billDays[thisPaymentDaysBeginBillIndex]=25
        thisPaymentDaysEndBillIndex=0 billDays[thisPaymentDaysEndBillIndex]=5
     */
    if (thisPaymentDays == null) {
        thisPaymentDays = new PaymentDays();
        calendar.set(Calendar.DAY_OF_MONTH, anyIndexOf(billDays, -1));
        thisPaymentDays.setBegin(calendar.getTime());
        calendar.add(Calendar.MONTH, 1);
        calendar.set(Calendar.DAY_OF_MONTH, anyIndexOf(billDays, 0));
        thisPaymentDays.setEnd(calendar.getTime());
    }
    if (nextCount == 0) { // 本账期
        nextPaymentDays = thisPaymentDays;
    } else {
        nextPaymentDays = new PaymentDays();

        calendar.setTimeInMillis(System.currentTimeMillis());
        calendar.set(Calendar.DAY_OF_MONTH, anyIndexOf(billDays, thisPaymentDaysBeginBillIndex + nextCount));
        int monthDvBegin = (int) Math.floor((thisPaymentDaysBeginBillIndex + nextCount) * 1.0 / paymentDaysDayLen);
        calendar.add(Calendar.MONTH, monthDvBegin);
        nextPaymentDays.setBegin(calendar.getTime());

        calendar.setTimeInMillis(System.currentTimeMillis());
        calendar.set(Calendar.DAY_OF_MONTH, anyIndexOf(billDays, thisPaymentDaysEndBillIndex + nextCount));
        int monthDvEnd = (int) Math.floor((thisPaymentDaysEndBillIndex + nextCount) * 1.0 / paymentDaysDayLen);
        calendar.add(Calendar.MONTH, monthDvEnd);
        nextPaymentDays.setEnd(calendar.getTime());
    }
    calendar.setTime(nextPaymentDays.getEnd());
    calendar.add(Calendar.DAY_OF_MONTH, -1); // 将账期变为既含前也含后
    nextPaymentDays.setEnd(calendar.getTime());
    return nextPaymentDays;
}

@Test
public void testPaymentDays() throws Exception {
    int[] ints = new int[]{25};
    for (int i = -6; i <= 6; i++) {
        if (i == 0) {
            System.out.println("===========");
        }
        System.out.println(nextPaymentDays(ints, i));
        if (i == 0) {
            System.out.println("===========");
        }
    }
    System.out.println("");
    System.out.println("");
    ints = new int[]{5, 15, 25};
    for (int i = -6; i <= 6; i++) {
        if (i == 0) {
            System.out.println("===========");
        }
        System.out.println(nextPaymentDays(ints, i));
        if (i == 0) {
            System.out.println("===========");
        }
    }

}