Java实现等额本息-蒲公英云

import java.math.BigDecimal;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.HashMap;
import java.util.Map;
/**
 * 等额本息
 */
public class EqualPrincipalInterestUtil {
    /**
     * 每期本金+利息
     * 公式：每月偿还本息=〔贷款本金×月利率×(1＋月利率)＾还款月数〕÷〔(1＋月利率)＾还款月数-1)
     * @param invest
     *            本金
     * @param periodRate
     *            每期利率
     * @param periodMonthNum
     *            期数
     * @return
     */
    public static double getPerPeriodPrincipalInterest(double invest, double periodRate, int periodMonthNum) {
        BigDecimal monthIncome = new BigDecimal(invest)
                .multiply(new BigDecimal(periodRate * Math.pow(1 + periodRate, periodMonthNum)))
                .divide(new BigDecimal(Math.pow(1 + periodRate, periodMonthNum) - 1), 4, BigDecimal.ROUND_HALF_UP);
        return monthIncome.doubleValue();
    }
    /**
     * 每期利息
     * 公式：每月偿还利息=贷款本金×月利率×〔(1+月利率)^还款月数-(1+月利率)^(还款月序号-1)〕÷〔(1+月利率)^还款月数-1〕
     * @param invest
     *            本金
     * @param periodRate
     *            每期利率
     * @param periodMonthNum
     *            期数
     * @return
     */
    public static Map<Integer, BigDecimal> getPerPeriodInterest(double invest, double periodRate, int periodMonthNum) {
        Map<Integer, BigDecimal> map = new HashMap<Integer, BigDecimal>();
        BigDecimal periodInterest;
        for (int i = 1; i < periodMonthNum + 1; i++) {
            BigDecimal multiply = new BigDecimal(invest).multiply(new BigDecimal(periodRate));
            BigDecimal sub = new BigDecimal(Math.pow(1 + periodRate, periodMonthNum))
                    .subtract(new BigDecimal(Math.pow(1 + periodRate, i - 1)));
            periodInterest = multiply.multiply(sub).divide(new BigDecimal(Math.pow(1 + periodRate, periodMonthNum) - 1),
                    6, BigDecimal.ROUND_HALF_UP);
            periodInterest = periodInterest.setScale(4, BigDecimal.ROUND_HALF_UP);
            map.put(i, periodInterest);
        }
        return map;
    }
    /**
     * 每期还款本金
     * 
     * @param invest
     *            本金
     * @param periodRate
     *            每期利率
     * @param periodNum
     *            期数
     * @return
     */
    public static Map<Integer, BigDecimal> getPerPeriodPrincipal(double invest, double periodRate, int periodNum) {
        BigDecimal monthIncome = new BigDecimal(invest)
                .multiply(new BigDecimal(periodRate * Math.pow(1 + periodRate, periodNum)))
                .divide(new BigDecimal(Math.pow(1 + periodRate, periodNum) - 1), 4, BigDecimal.ROUND_HALF_UP);
        Map<Integer, BigDecimal> mapInterest = getPerPeriodInterest(invest, periodRate, periodNum);
        Map<Integer, BigDecimal> mapPrincipal = new HashMap<Integer, BigDecimal>();
        for (Map.Entry<Integer, BigDecimal> entry : mapInterest.entrySet()) {
            mapPrincipal.put(entry.getKey(), monthIncome.subtract(entry.getValue()));
        }
        return mapPrincipal;
    }
    /**
     * 总利息
     * 
     * @param invest
     *            本金
     * @param periodRate
     *            每期利率
     * @param periodNum
     *            期数
     * @return
     */
    public static double getInterestCount(double invest, double periodRate, int periodNum) {
        BigDecimal count = new BigDecimal(0);
        Map<Integer, BigDecimal> mapInterest = getPerPeriodInterest(invest, periodRate, periodNum);
        for (Map.Entry<Integer, BigDecimal> entry : mapInterest.entrySet()) {
            count = count.add(entry.getValue());
        }
        return count.doubleValue();
    }
    /**
     * 本息总和
     * 
     * @param invest
     *            本金
     * @param periodRate
     *            每期利率
     * @param periodNum
     *            期数
     * @return
     */
    public static double getPrincipalInterestCount(double invest, double periodRate, int periodNum) {
        BigDecimal perMonthInterest = new BigDecimal(invest);
        Map<Integer, BigDecimal> mapInterest = getPerPeriodInterest(invest, periodRate, periodNum);
        for (Map.Entry<Integer, BigDecimal> entry : mapInterest.entrySet()) {
            perMonthInterest = perMonthInterest.add(entry.getValue());
        }
        return perMonthInterest.doubleValue();
    }
    /**
     * 每期还款日期
     * @param start_date
     *                 起租日
     * @param perPeriodMonthNum
     *                 每期月数
     * @param periodNum
     *                 期数
     * @return
     */
    public static Map<Integer, String> getRepaymentDate(String start_date, int perPeriodMonthNum, int periodNum) {
        Map<Integer, String> periodRepaymentDate = new HashMap<Integer, String>();
        String nextRepaymentDate = start_date;
        periodRepaymentDate.put(1, nextRepaymentDate);
        for (int i = 2; i < periodNum + 1; i++) {
            nextRepaymentDate = getMonthAdd(perPeriodMonthNum, nextRepaymentDate, "yyyyMMdd");
            periodRepaymentDate.put(i, nextRepaymentDate);
        }
        return periodRepaymentDate;
    }
    /**
     * 功能描述：返回指定日期加上多少月之后的时间<BR>
     * @param from   yyyyMMdd
     * @param day
     * @param formatStr
     * @return
     */
    public static String getMonthAdd(int day,String from,String formatStr){
        SimpleDateFormat sdf=new SimpleDateFormat(formatStr);
        Calendar calendar = Calendar.getInstance();
        try {
            calendar.setTime(sdf.parse(from));
        } catch (Exception e) {
            e.printStackTrace();
        }
        calendar.add(Calendar.MONTH, day);
        String date = sdf.format(calendar.getTime());
        return date;
    }
    public static void main(String[] args) {  
        double invest = 10000; // 本金  
        int periodNum = 4;
        double periodRate = 0.12/3; // 年利率  
        System.out.println("等额本息---本金：" + invest);  
        double perMonthPrincipalInterest = getPerPeriodPrincipalInterest(invest, periodRate, periodNum);  
        System.out.println("等额本息---每期还款本息：" + perMonthPrincipalInterest);  
        Map<Integer, BigDecimal> mapInterest = getPerPeriodInterest(invest, periodRate, periodNum);  
        System.out.println("等额本息---每期还款利息：" + mapInterest);  
        Map<Integer, BigDecimal> mapPrincipal = getPerPeriodPrincipal(invest, periodRate, periodNum);  
        System.out.println("等额本息---每期还款本金：" + mapPrincipal);  
        double count = getInterestCount(invest, periodRate, periodNum);  
        System.out.println("等额本息---总利息：" + count);  
        double principalInterestCount = getPrincipalInterestCount(invest, periodRate, periodNum);  
        System.out.println("等额本息---应还本息总和：" + principalInterestCount);  
    }
}