第四章聚合 - 重构售货机聚合 - 《Domain Driven Design with Spring Boot》

首先我们对Snack和SnackMachine重构：

package com.lugew.springbootddd;
import lombok.Getter;
import lombok.Setter;
/**
 * @author 夏露桂
 * @since 2021/6/16 10:45
 */
@Getter
@Setter
public class Snack extends AggregateRoot {
    private String name;
    public Snack() {
    }
    public Snack(String name) {
        this.name = name;
    }
}

package com.lugew.springbootddd.snackmachine;
import com.lugew.springbootddd.AggregateRoot;
import com.lugew.springbootddd.Slot;
import com.lugew.springbootddd.Snack;
import com.lugew.springbootddd.SnackMachineDto;
import lombok.Getter;
import lombok.Setter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import static com.lugew.springbootddd.snackmachine.Money.None;
@Getter
@Setter
public final class SnackMachine extends AggregateRoot {
    private Money moneyInside;
    private Money moneyInTransaction;
    private List<Slot> slots;
    public SnackMachine() {
        moneyInside = None;
        moneyInTransaction = None;
        slots = new ArrayList<>();
        slots.add(new Slot(this, 1, null, 0, 1));
        slots.add(new Slot(this, 2, null, 0, 1));
        slots.add(new Slot(this, 3, null, 0, 1));
    }
    public void insertMoney(Money money) {
        Money[] coinsAndNotes = {Money.Cent, Money.TenCent, Money.Quarter,
                Money.Dollar, Money.FiveDollar,
                Money.TwentyDollar};
        if (!Arrays.asList(coinsAndNotes).contains(money))
            throw new IllegalStateException();
        moneyInTransaction = Money.add(moneyInTransaction, money);
    }
    public void returnMoney() {
        moneyInTransaction = None;
    }
    public void buySnack(int position) {
        Slot slot = slots.stream().filter(x -> x.getPosition() ==
                position).findAny().orElse(null);
        slot.setQuantity(slot.getQuantity() - 1);
        moneyInside = Money.add(moneyInside, moneyInTransaction);
        moneyInTransaction = None;
    }
    public SnackMachineDto convertToSnackMachineDto() {
        SnackMachineDto snackMachineDto = new SnackMachineDto();
        snackMachineDto.setId(id);
        snackMachineDto.setMoneyInTransaction(moneyInTransaction.getAmount());
        snackMachineDto.setOneCentCount(moneyInside.getOne、
                                        CentCount());
        snackMachineDto.setTenCentCount(moneyInside.getTenCentCount());
        snackMachineDto.setQuarterCount(moneyInside.getQuarterCount());
        snackMachineDto.setOneDollarCount(moneyInside.getOneDollarCount());
        snackMachineDto.setFiveDollarCount(moneyInside.getFiveDollarCount());
        snackMachineDto.setTwentyDollarCount(moneyInside.getTwentyDollarCount());
        return snackMachineDto;
    }
    public void loadSnacks(int position, Snack snack, int quantity, float price) {
        Slot slot = slots.stream().filter(x -> x.getPosition() ==
                position).findAny().orElse(null);
        if (slot != null) {
            slot.setSnack(snack);
            slot.setQuantity(quantity);
            slot.setPrice(price);
        }
    }
}

此时，我们还有几处需要重构，一，List对外暴露，这是应该避免的，二，Slot类也是能够被外界访问的，这违背了我们之前提到过的外界隔离原则。避免对外暴露通常不会太容易，在我们的例子中，只要将getter和setter方法隐藏即可：

package com.lugew.springbootddd.snackmachine;
import com.lugew.springbootddd.AggregateRoot;
import com.lugew.springbootddd.Slot;
import com.lugew.springbootddd.Snack;
import com.lugew.springbootddd.SnackMachineDto;
import lombok.Getter;
import lombok.Setter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import static com.lugew.springbootddd.snackmachine.Money.None;
public final class SnackMachine extends AggregateRoot {
    @Getter
    @Setter
    private Money moneyInside;
    @Getter
    @Setter
    private Money moneyInTransaction;
    private List<Slot> slots;
    public SnackMachine() {
        moneyInside = None;
        moneyInTransaction = None;
        slots = new ArrayList<>();
        slots.add(new Slot(this, 1, null, 0, 1));
        slots.add(new Slot(this, 2, null, 0, 1));
        slots.add(new Slot(this, 3, null, 0, 1));
    }
    public void insertMoney(Money money) {
        Money[] coinsAndNotes = {Money.Cent, Money.TenCent, Money.Quarter,
                Money.Dollar, Money.FiveDollar,
                Money.TwentyDollar};
        if (!Arrays.asList(coinsAndNotes).contains(money))
            throw new IllegalStateException();
        moneyInTransaction = Money.add(moneyInTransaction, money);
    }
    public void returnMoney() {
        moneyInTransaction = None;
    }
    public void buySnack(int position) {
        Slot slot = slots.stream().filter(x -> x.getPosition() ==
                position).findAny().orElse(null);
        slot.setQuantity(slot.getQuantity() - 1);
        moneyInside = Money.add(moneyInside, moneyInTransaction);
        moneyInTransaction = None;
    }
    public SnackMachineDto convertToSnackMachineDto() {
        SnackMachineDto snackMachineDto = new SnackMachineDto();
        snackMachineDto.setId(id);
        snackMachineDto.setMoneyInTransaction(moneyInTransaction.getAmount());
        snackMachineDto.setOneCentCount(moneyInside.getOneCentCount());
        snackMachineDto.setTenCentCount(moneyInside.getTenCentCount());
        snackMachineDto.setQuarterCount(moneyInside.getQuarterCount());
        snackMachineDto.setOneDollarCount(moneyInside.getOneDollarCount());
        snackMachineDto.setFiveDollarCount(moneyInside.getFiveDollarCount());
        snackMachineDto.setTwentyDollarCount(moneyInside.getTwentyDollarCount());
        return snackMachineDto;
    }
    public void loadSnacks(int position, Snack snack, int quantity, float price) {
        Slot slot = slots.stream().filter(x -> x.getPosition() ==
                position).findAny().orElse(null);
        if (slot != null) {
            slot.setSnack(snack);
            slot.setQuantity(quantity);
            slot.setPrice(price);
        }
    }
}

为了解决上述问题，我们可能会添加一个返回指定位置的插槽中零食数量的方法：snackMachine.getQuantityOfSnacksInSlot(1)，且该方法的返回值是9。但这种方式会带来其他的问题，当我们需要插槽的其他信息时，如零食信息及其价格，那么我们必须再添加两个方法：getSnackInSlot和``getPriceInSlot。当要获取所有插槽和零食时，使用这些方法就变得异常繁琐。我们必须采取另一种方式，之前的文章中我们说过，当代码使用变得冗余时，意味着存在隐藏的抽象，Slot类中含有三个属性：Snack、Quantity和Price。这三个属性始终绑定在一起，所以我们能将之重构为一个值对象。这很有用，值对象将紧耦合的属性同时暴露。我们为之新建值对象的抽象：SnackPile：

package com.lugew.springbootddd;
import lombok.Getter;
/**
 * @author 夏露桂
 * @since 2021/6/22 17:52
 */
@Getter
public class SnackPile extends ValueObject<SnackPile> {
    private Snack snack;
    private int quantity;
    private float price;
    private SnackPile() {
    }
    public SnackPile(Snack snack, int quantity, float price) {
        this.snack = snack;
        this.quantity = quantity;
        this.price = price;
    }
    public SnackPile subtractOne() {
        return new SnackPile(snack, getQuantity() - 1, getPrice());
    }
    @Override
    protected boolean equalsCore(SnackPile other) {
        return this.snack == other.snack && this.getQuantity() == other.getQuantity()
                && this.getPrice() == other.getPrice();
    }
    @Override
    protected int getHashCodeCore() {
        final int prime = 31;
        int result = super.hashCode();
        result = prime * result + Float.floatToIntBits(price);
        result = prime * result + quantity;
        result = prime * result + ((snack == null) ? 0 : snack.hashCode());
        return result;
    }
}

我们只给值对象生成get方法，保持其不可变性。随后我们重构SnackMachine属性和方法：

package com.lugew.springbootddd.snackmachine;
import com.lugew.springbootddd.AggregateRoot;
import com.lugew.springbootddd.Slot;
import com.lugew.springbootddd.SnackMachineDto;
import com.lugew.springbootddd.SnackPile;
import lombok.Getter;
import lombok.Setter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import static com.lugew.springbootddd.snackmachine.Money.None;
public final class SnackMachine extends AggregateRoot {
    @Getter
    @Setter
    private Money moneyInside;
    @Getter
    @Setter
    private Money moneyInTransaction;
    private List<Slot> slots;
    public SnackMachine() {
        moneyInside = None;
        moneyInTransaction = None;
        slots = new ArrayList<>();
        slots.add(new Slot(this, 1));
        slots.add(new Slot(this, 2));
        slots.add(new Slot(this, 3));
    }
    public void insertMoney(Money money) {
        Money[] coinsAndNotes = {Money.Cent, Money.TenCent, Money.Quarter,
                Money.Dollar, Money.FiveDollar,
                Money.TwentyDollar};
        if (!Arrays.asList(coinsAndNotes).contains(money))
            throw new IllegalStateException();
        moneyInTransaction = Money.add(moneyInTransaction, money);
    }
    public void returnMoney() {
        moneyInTransaction = None;
    }
    public void buySnack(int position) {
        Slot slot = slots.stream().filter(x -> x.getPosition() ==
                position).findAny().orElse(null);
        slot.setSnackPile(slot.getSnackPile().subtractOne());
        moneyInside = Money.add(moneyInside, moneyInTransaction);
        moneyInTransaction = None;
    }
    public SnackMachineDto convertToSnackMachineDto() {
        SnackMachineDto snackMachineDto = new SnackMachineDto();
        snackMachineDto.setId(id);
        snackMachineDto.setMoneyInTransaction(moneyInTransaction.getAmount());
        snackMachineDto.setOneCentCount(moneyInside.getOneCentCount());
        snackMachineDto.setTenCentCount(moneyInside.getTenCentCount());
        snackMachineDto.setQuarterCount(moneyInside.getQuarterCount());
        snackMachineDto.setOneDollarCount(moneyInside.getOneDollarCount());
        snackMachineDto.setFiveDollarCount(moneyInside.getFiveDollarCount());
        snackMachineDto.setTwentyDollarCount(moneyInside.getTwentyDollarCount());
        return snackMachineDto;
    }
    public void loadSnacks(int position, SnackPile snackPile) {
        Slot slot = slots.stream().filter(x -> x.getPosition() ==
                position).findAny().orElse(null);
        if (slot != null) {
            slot.setSnackPile(snackPile);
        }
    }
    public SnackPile getSnackPile(int position) {
        return slots.stream().filter(x -> x.getPosition() ==
                position).findAny().orElse(null).getSnackPile();
    }
}

我们还需要为SnackPile添加数量减少的功能，一种方法直接设置quality，这种方式非常不可取，它破坏了值对象的不可变性，取而代之的是提供公共方法，返回一个除quality外都相同的新对象。

package com.lugew.springbootddd;
import lombok.Getter;
/**
 * @author 夏露桂
 * @since 2021/6/22 17:52
 */
@Getter
public class SnackPile extends ValueObject<SnackPile> {
    private Snack snack;
    private int quantity;
    private float price;
    private SnackPile() {
    }
    public SnackPile(Snack snack, int quantity, float price) {
        this.snack = snack;
        this.quantity = quantity;
        this.price = price;
    }
    public SnackPile subtractOne() {
        return new SnackPile(snack, getQuantity() - 1, getPrice());
    }
    @Override
    protected boolean equalsCore(SnackPile other) {
        return this.snack == other.snack && this.getQuantity() == other.getQuantity()
                && this.getPrice() == other.getPrice();
    }
    @Override
    protected int getHashCodeCore() {
        final int prime = 31;
        int result = super.hashCode();
        result = prime * result + Float.floatToIntBits(price);
        result = prime * result + quantity;
        result = prime * result + ((snack == null) ? 0 : snack.hashCode());
        return result;
    }
}

最后重构测试：

    @Test
    public void buySnack_trades_inserted_money_for_a_snack() {
        SnackMachine snackMachine = new SnackMachine();
        snackMachine.loadSnacks(1, new SnackPile(new Snack("Some snack"), 10, 1));
        snackMachine.insertMoney(Dollar);
        snackMachine.buySnack(1);
        assertEquals(snackMachine.getMoneyInTransaction(), Money.None);
        assertEquals(snackMachine.getMoneyInside().getAmount(), 1, 0.5);
        assertEquals(snackMachine.getSnackPile(1).getQuantity(), 9);
    }

接下来还有一些方法需要重构：

    public void buySnack(int position) {
        Slot slot = getSlot(position);
        slot.setSnackPile(slot.getSnackPile().subtractOne());
        moneyInside = Money.add(moneyInside, moneyInTransaction);
        moneyInTransaction = None;
    }
    public Slot getSlot(int position) {
        return slots.stream().filter(x -> x.getPosition() ==
                position).findAny().orElse(null);
    }
    public SnackPile getSnackPile(int position) {
        return getSlot(position).getSnackPile();
    }

同时还有SnackPile：

package com.lugew.springbootddd;
import lombok.Getter;
/**
 * @author 夏露桂
 * @since 2021/6/22 17:52
 */
@Getter
public class SnackPile extends ValueObject<SnackPile> {
    private Snack snack;
    private int quantity;
    private float price;
    private SnackPile() {
    }
    public SnackPile(Snack snack, int quantity, float price) {
        if (quantity < 0)
            throw new IllegalStateException();
        if (price < 0)
            throw new IllegalStateException();
        this.snack = snack;
        this.quantity = quantity;
        this.price = price;
    }
    public SnackPile subtractOne() {
        return new SnackPile(snack, getQuantity() - 1, getPrice());
    }
    @Override
    protected boolean equalsCore(SnackPile other) {
        return this.snack == other.snack && this.getQuantity() == other.getQuantity()
                && this.getPrice() == other.getPrice();
    }
    @Override
    protected int getHashCodeCore() {
        final int prime = 31;
        int result = super.hashCode();
        result = prime * result + Float.floatToIntBits(price);
        result = prime * result + quantity;
        result = prime * result + ((snack == null) ? 0 : snack.hashCode());
        return result;
    }
}

添加异常判断，此部分的单元测试读者可自行实现。