先看看结构图：
    image.png
    为了实现购买功能，需要增加两个新实体：Snack零食和Slot零食槽
    image.png
    Snack类只有name字段，Slot实体链接Snack和SnackMachine，同时也包含自身信息：位置，价格和数量。

    1. package com.lugew.springbootddd;
    3. import lombok.Getter;
    4. import lombok.Setter;
    6. /**
    7.  * @author 夏露桂
    8.  * @since 2021/6/16 10:45
    9.  */
    10. @Getter
    11. @Setter
    12. public class Snack extends Entity {
    13.     private String name;
    15.     public Snack() {
    16.     }
    18.     public Snack(String name) {
    19.         this.name = name;
    20.     }
    22. }

    显然，Snack是实体。另一个实体是Slot：

    1. package com.lugew.springbootddd;
    3. import com.lugew.springbootddd.snackmachine.SnackMachine;
    4. import lombok.Getter;
    5. import lombok.Setter;
    7. /**
    8.  * @author 夏露桂
    9.  * @since 2021/6/16 10:47
    10.  */
    11. @Getter
    12. @Setter
    13. public class Slot extends Entity {
    14.     private Snack snack;
    15.     private int quantity;
    16.     private float price;
    17.     private SnackMachine snackMachine;
    18.     private int position;
    20.     public Slot() {
    21.     }
    23.     public Slot(SnackMachine snackMachine, int position, Snack snack, int quantity,
    24.                 float price) {
    25.         this.snackMachine = snackMachine;
    26.         this.position = position;
    27.         this.snack = snack;
    28.         this.quantity = quantity;
    29.         this.price = price;
    30.     }
    31. }

    此时，重构测试方法money_in_transaction_goes_to_money_inside_after_purchase至buySnack_trades_inserted_money_for_a_snack：

    1.     @Test
    2.     public void buySnack_trades_inserted_money_for_a_snack() {
    3.         SnackMachine snackMachine = new SnackMachine();
    4.         snackMachine.loadSnacks(1, new Snack("Some snack"), 10, 1);
    5.         snackMachine.insertMoney(Dollar);
    6.         snackMachine.buySnack(1);
    7.         assertEquals(snackMachine.getMoneyInTransaction(),
    8.                 0);
    9.         assertEquals(snackMachine.getMoneyInside().getAmount(), 1, 0.5);
    10.         Slot slot = snackMachine.getSlots().stream().filter(x -> x.getPosition() ==
    11.                 1).findAny().orElse(null);
    12.         assertEquals(slot.getQuantity(), 9);
    13.     }

    和SnackMachine：

    1. package com.lugew.springbootddd.snackmachine;
    3. import com.lugew.springbootddd.Entity;
    4. import com.lugew.springbootddd.Slot;
    5. import com.lugew.springbootddd.Snack;
    6. import com.lugew.springbootddd.SnackMachineDto;
    7. import lombok.Getter;
    8. import lombok.Setter;
    10. import java.util.Arrays;
    11. import java.util.List;
    13. import static com.lugew.springbootddd.snackmachine.Money.None;
    15. @Getter
    16. @Setter
    17. public final class SnackMachine extends Entity {
    18.     private Money moneyInside;
    19.     private Money moneyInTransaction;
    20.     private List<Slot> slots;
    22.     public SnackMachine() {
    23.         moneyInside = None;
    24.         moneyInTransaction = None;
    25.         slots = new ArrayList<>();
    26.         slots.add(new Slot(this, 1, null, 0, 1));
    27.         slots.add(new Slot(this, 2, null, 0, 1));
    28.         slots.add(new Slot(this, 3, null, 0, 1));
    29.     }
    31.     public void insertMoney(Money money) {
    32.         Money[] coinsAndNotes = {Money.Cent, Money.TenCent, Money.Quarter,
    33.                 Money.Dollar, Money.FiveDollar,
    34.                 Money.TwentyDollar};
    35.         if (!Arrays.asList(coinsAndNotes).contains(money))
    36.             throw new IllegalStateException();
    38.         moneyInTransaction = Money.add(moneyInTransaction, money);
    40.     }
    42.     public void returnMoney() {
    43.         moneyInTransaction = None;
    44.     }
    47.     public void buySnack(int position) {
    48.         Slot slot = slots.stream().filter(x -> x.getPosition() ==
    49.                 position).findAny().orElse(null);
    50.         slot.setQuantity(slot.getQuantity() - 1);
    51.         moneyInside = Money.add(moneyInside, moneyInTransaction);
    52.         moneyInTransaction = None;
    53.     }
    55.     public SnackMachineDto convertToSnackMachineDto() {
    56.         SnackMachineDto snackMachineDto = new SnackMachineDto();
    57.         snackMachineDto.setId(id);
    58.         snackMachineDto.setMoneyInTransaction(moneyInTransaction.getAmount());
    59.         snackMachineDto.setOneCentCount(moneyInside.getOneCentCount());
    60.         snackMachineDto.setTenCentCount(moneyInside.getTenCentCount());
    61.         snackMachineDto.setQuarterCount(moneyInside.getQuarterCount());
    62.         snackMachineDto.setOneDollarCount(moneyInside.getOneDollarCount());
    63.         snackMachineDto.setFiveDollarCount(moneyInside.getFiveDollarCount());
    64.         snackMachineDto.setTwentyDollarCount(moneyInside.getTwentyDollarCount());
    65.         return snackMachineDto;
    66.     }
    68.     public void loadSnacks(int position, Snack snack, int quantity, float price) {
    69.         Slot slot = slots.stream().filter(x -> x.getPosition() ==
    70.                 position).findAny().orElse(null);
    71.         if (slot != null) {
    72.             slot.setSnack(snack);
    73.             slot.setQuantity(quantity);
    74.             slot.setPrice(price);
    75.         }
    76.     }
    77. }

    此外，还有SnackMachineController：

    1. package com.lugew.springbootddd;
    3. import com.lugew.springbootddd.snackmachine.Money;
    4. import com.lugew.springbootddd.snackmachine.SnackMachine;
    5. import lombok.RequiredArgsConstructor;
    6. import org.springframework.web.bind.annotation.*;
    8. import static com.lugew.springbootddd.snackmachine.Money.*;
    10. /**
    11.  * @author 夏露桂
    12.  * @since 2021/6/10 11:55
    13.  */
    14. @RestController
    15. @RequestMapping("snackmachines")
    16. @RequiredArgsConstructor
    17. public class SnackMachineController {
    18.     private final SnackMachineRepository snackMachineRepository;
    20.     @GetMapping("/{id}")
    21.     @ResponseBody
    22.     public SnackMachineDto getSnackMachine(@PathVariable("id") long id) {
    23.         return snackMachineRepository.findById(id).orElse(null);
    24.     }
    26.     @PutMapping("/{id}/{slotNumber}")
    27.     public void buySnack(@PathVariable("id") long id, @PathVariable("slotNumber")
    28.             int slotNumber) {
    29.         SnackMachineDto snackMachineDto =
    30.                 snackMachineRepository.findById(id).orElse(null);
    31.         SnackMachine snackMachine = snackMachineDto.convertToSnackMachine();
    32.         snackMachine.buySnack(slotNumber);
    33.         snackMachineRepository.save(snackMachine.convertToSnackMachineDto());
    34.     }
    36.     @PutMapping("/{id}/moneyInTransaction/{coinOrNote}")
    37.     public void insertCoinOrNote(@PathVariable("id") long id, @PathVariable("coinOrNote") String coinOrNote) {
    38.         SnackMachineDto snackMachineDto =
    39.                 snackMachineRepository.findById(id).orElse(null);
    40.         SnackMachine snackMachine = snackMachineDto.convertToSnackMachine();
    41.         if (coinOrNote.equalsIgnoreCase("Cent")) snackMachine.insertMoney(Cent);
    42.         else if (coinOrNote.equalsIgnoreCase("TenCent"))
    43.             snackMachine.insertMoney(TenCent);
    44.         else if (coinOrNote.equalsIgnoreCase("Quarter"))
    45.             snackMachine.insertMoney(Quarter);
    46.         else if (coinOrNote.equalsIgnoreCase("Dollar"))
    47.             snackMachine.insertMoney(Dollar);
    48.         else if (coinOrNote.equalsIgnoreCase("FiveDollar"))
    49.             snackMachine.insertMoney(FiveDollar);
    50.         else if (coinOrNote.equalsIgnoreCase("TwentyDollar"))
    51.             snackMachine.insertMoney(TwentyDollar);
    52.         snackMachineRepository.save(snackMachine.convertToSnackMachineDto());
    53.     }
    55.     @PutMapping("/{id}/moneyInTransaction")
    56.     public void returnMoney(@PathVariable("id") long id) {
    57.         SnackMachineDto snackMachineDto =
    58.                 snackMachineRepository.findById(id).orElse(null);
    59.         SnackMachine snackMachine = snackMachineDto.convertToSnackMachine();
    60.         snackMachine.returnMoney();
    61.         snackMachineRepository.save(snackMachine.convertToSnackMachineDto());
    62.     }
    64.     public Money getWholeMoney(SnackMachine snackMachine) {
    65.         return Money.add(snackMachine.getMoneyInside(), snackMachine.getMoneyInTransaction());
    66.     }
    68. }

    查看测试：
    image.png
    buySnack功能的缺陷先不谈，说说设计模式。