BigDecimal，ROUND_UP的进位制

java.math包中提供的API类BigDecimal，对超过16位有效位的数进行精确的运算。BigDecimal.ROUND_UP，进位制：不管保留数字后面是大是小（0除外）都会进1。

案例代码：

 public class BigDecimalDemo {

    public static void main(String[] args) {
        BigDecimal numOne = new BigDecimal("3.14959267");
        BigDecimal numTwo = new BigDecimal("3.3205667");
        BigDecimal numThree = new BigDecimal("3.3005667");
        BigDecimal numOneRound = numOne.setScale(2, BigDecimal.ROUND_UP);
        System.out.println("numOneRound:" + numOneRound);  // 3.15
        BigDecimal numTwoRound = numTwo.setScale(2, BigDecimal.ROUND_UP);
        System.out.println("numTwoRound:" + numTwoRound); // 3.33
        BigDecimal numThreeRound = numThree.setScale(2, BigDecimal.ROUND_UP);
        System.out.println("numThreeRound:" + numThreeRound); // 3.31
    }

}  

参考：

商品单位的价格换算工具

之前 的基础上，商品单位设定其中一种类型的价格，其他价格已同时设定。

 import java.math.BigDecimal;
import java.util.LinkedHashMap;

public class UnitPriceTools {

    /**
     * 设置一个单位的价格，自动生成所有的价格
     *
     * @param unitGroupMap
     * @param unitType
     * @param unitPrice
     * @param model
     * @return
     */    public static LinkedHashMap<Integer, BigDecimal> toUnitPriceMapWithType(LinkedHashMap<Integer, Unit> unitGroupMap, int unitType, BigDecimal unitPrice, int model) {
        LinkedHashMap<Integer, BigDecimal> unitPriceMap = new LinkedHashMap<>();
        if (unitType == 1) {
            // 单位类型1
            unitPriceMap.put(1, unitPrice.setScale(2));
            // 单位类型2
            BigDecimal unitPrice2 = unitPrice.multiply(new BigDecimal(unitGroupMap.get(2).getUnitValue())).setScale(2);
            unitPriceMap.put(2, unitPrice2);
            // 单位类型3
            BigDecimal unitPrice3 = unitPrice2.multiply(new BigDecimal(unitGroupMap.get(3).getUnitValue())).setScale(2);
            unitPriceMap.put(3, unitPrice3);
            // 单位类型4
            BigDecimal unitPrice4 = unitPrice3.multiply(new BigDecimal(unitGroupMap.get(4).getUnitValue())).setScale(2);
            unitPriceMap.put(4, unitPrice4);
        } else if (unitType == 2) {
            // 单位类型1
            BigDecimal unit1Price = unitPrice.divide(new BigDecimal(unitGroupMap.get(2).getUnitValue()));
            BigDecimal unit1RoundPrice = unit1Price.setScale(2, BigDecimal.ROUND_UP);
            if (model == 0) {
                unitPriceMap.put(11, unit1Price);
                unitPriceMap.put(1, unit1RoundPrice);
            } else {
                unitPriceMap.put(1, unit1RoundPrice);
            }
            // 单位类型2
            unitPriceMap.put(2, unitPrice.setScale(2));
            // 单位类型3
            BigDecimal unitPrice3 = unitPrice.multiply(new BigDecimal(unitGroupMap.get(3).getUnitValue())).setScale(2);
            unitPriceMap.put(3, unitPrice3);
            // 单位类型4
            BigDecimal unitPrice4 = unitPrice3.multiply(new BigDecimal(unitGroupMap.get(4).getUnitValue())).setScale(2);
            unitPriceMap.put(4, unitPrice4);
        } else if (unitType == 3) {
            // 单位类型2
            BigDecimal unit2Price = unitPrice.divide(new BigDecimal(unitGroupMap.get(3).getUnitValue()));
            BigDecimal unit2RoundPrice = unit2Price.setScale(2, BigDecimal.ROUND_UP);
            if (model == 0) {
                unitPriceMap.put(21, unit2Price);
                unitPriceMap.put(2, unit2RoundPrice);
            } else {
                unitPriceMap.put(2, unit2RoundPrice);
            }
            // 单位类型1
            BigDecimal unit1Price = unit2Price.divide(new BigDecimal(unitGroupMap.get(2).getUnitValue()));
            BigDecimal unit1RoundPrice = unit1Price.setScale(2, BigDecimal.ROUND_UP);
            if (model == 0) {
                unitPriceMap.put(11, unit1Price);
                unitPriceMap.put(1, unit1RoundPrice);
            } else {
                unitPriceMap.put(1, unit1RoundPrice);
            }
            // 单位类型3
            unitPriceMap.put(3, unitPrice.setScale(2));
            // 单位类型4
            BigDecimal unitPrice4 = unitPrice.multiply(new BigDecimal(unitGroupMap.get(4).getUnitValue())).setScale(2);
            unitPriceMap.put(4, unitPrice4);
        } else if (unitType == 4) {
            // 单位类型3
            BigDecimal unit3Price = unitPrice.divide(new BigDecimal(unitGroupMap.get(4).getUnitValue()));
            BigDecimal unit3RoundPrice = unit3Price.setScale(2, BigDecimal.ROUND_UP);
            if (model == 0) {
                unitPriceMap.put(31, unit3Price);
                unitPriceMap.put(3, unit3RoundPrice);
            } else {
                unitPriceMap.put(3, unit3RoundPrice);
            }
            // 单位类型2
            BigDecimal unit2Price = unit3Price.divide(new BigDecimal(unitGroupMap.get(3).getUnitValue()));
            BigDecimal unit2RoundPrice = unit2Price.setScale(2, BigDecimal.ROUND_UP);
            if (model == 0) {
                unitPriceMap.put(21, unit2Price);
                unitPriceMap.put(2, unit2RoundPrice);
            } else {
                unitPriceMap.put(2, unit2RoundPrice);
            }
            // 单位类型1
            BigDecimal unit1Price = unit2Price.divide(new BigDecimal(unitGroupMap.get(2).getUnitValue()));
            BigDecimal unit1RoundPrice = unit1Price.setScale(2, BigDecimal.ROUND_UP);
            if (model == 0) {
                unitPriceMap.put(11, unit1Price);
                unitPriceMap.put(1, unit1RoundPrice);
            } else {
                unitPriceMap.put(1, unit1RoundPrice);
            }
            // 单位类型4
            unitPriceMap.put(4, unitPrice.setScale(2));
        }
        return unitPriceMap;
    }

    /**
     * @param unitGroupMap
     * @param unitType
     * @param unitPrice
     * @return
     */    public static LinkedHashMap<Integer, BigDecimal> toUnitPriceMapWithType(LinkedHashMap<Integer, Unit> unitGroupMap, int unitType, BigDecimal unitPrice) {
        return toUnitPriceMapWithType(unitGroupMap, unitType, unitPrice, 1);
    }

}  

工具类测试：

 import java.math.BigDecimal;
import java.util.LinkedHashMap;
import java.util.List;

public class UnitPriceToolsTest {

    public static void main(String[] args) {
        // 准备商品
        Long goodsId = 1000L;
        // 准备商品单位列表
        List<Unit> unitList = UnitConvertService.getUnitList(goodsId);
        // =======================================================================================//
        // >>>>>>>>>>>> 按类型分组返回保证顺序的Map（根据单位类型）
        LinkedHashMap<Integer, Unit> unitGroupMap = UnitConvertTools.toUnitMapWithType(goodsId, unitList);
        System.out.println("按类型分组返回保证顺序的Map（根据单位类型） = " + unitGroupMap);
        LinkedHashMap<Integer, BigDecimal> unitType1PriceMap = UnitPriceTools.toUnitPriceMapWithType(unitGroupMap, 1, new BigDecimal("1.11"));
        System.out.println("单位类型1，价格 = " + unitType1PriceMap);
        LinkedHashMap<Integer, BigDecimal> unitType2PriceMap = UnitPriceTools.toUnitPriceMapWithType(unitGroupMap, 2, new BigDecimal("44.14"), 0);
        System.out.println("单位类型2，价格 = " + unitType2PriceMap);
        LinkedHashMap<Integer, BigDecimal> unitType3PriceMap = UnitPriceTools.toUnitPriceMapWithType(unitGroupMap, 3, new BigDecimal("444.10"), 0);
        System.out.println("单位类型3，价格 = " + unitType3PriceMap);
        LinkedHashMap<Integer, BigDecimal> unitType4PriceMap = UnitPriceTools.toUnitPriceMapWithType(unitGroupMap, 4, new BigDecimal("8888"), 0);
        System.out.println("单位类型4，价格 = " + unitType4PriceMap);
    }

}  

测试输出内容：

 单位类型1，价格 = {1=1.11, 2=44.40, 3=444.00, 4=8880.00}
单位类型2，价格 = {11=1.1035, 1=1.11, 2=44.14, 3=441.40, 4=8828.00}
单位类型3，价格 = {21=44.41, 2=44.41, 11=1.11025, 1=1.12, 3=444.10, 4=8882.00}
单位类型4，价格 = {31=444.4, 3=444.40, 21=44.44, 2=44.44, 11=1.111, 1=1.12, 4=8888.00}