DDD领域驱动设计1

public class VirtualWallet { // Domain领域模型(充血模型)
  private Long id;
  private Long createTime = System.currentTimeMillis();;
  private BigDecimal balance = BigDecimal.ZERO;
  
  public VirtualWallet(Long preAllocatedId) {
    this.id = preAllocatedId;
  }
  
  public BigDecimal balance() {
    return this.balance;
  }
  
  public void debit(BigDecimal amount) {
    if (this.balance.compareTo(amount) < 0) {
      throw new InsufficientBalanceException(...);
    }
    this.balance.subtract(amount);
  }
  
  public void credit(BigDecimal amount) {
    if (amount.compareTo(BigDecimal.ZERO) < 0) {
      throw new InvalidAmountException(...);
    }
    this.balance.add(amount);
  }
}

public class VirtualWalletService {
  // 通过构造函数或者IOC框架注入
  private VirtualWalletRepository walletRepo;
  private VirtualWalletTransactionRepository transactionRepo;
  
  public VirtualWallet getVirtualWallet(Long walletId) {
    VirtualWalletEntity walletEntity = walletRepo.getWalletEntity(walletId);
    VirtualWallet wallet = convert(walletEntity);
    return wallet;
  }
  
  public BigDecimal getBalance(Long walletId) {
    return walletRepo.getBalance(walletId);
  }
  
  public void debit(Long walletId, BigDecimal amount) {
    VirtualWalletEntity walletEntity = walletRepo.getWalletEntity(walletId);
    VirtualWallet wallet = convert(walletEntity);
    wallet.debit(amount);
    walletRepo.updateBalance(walletId, wallet.balance());
  }
  
  public void credit(Long walletId, BigDecimal amount) {
    VirtualWalletEntity walletEntity = walletRepo.getWalletEntity(walletId);
    VirtualWallet wallet = convert(walletEntity);
    wallet.credit(amount);
    walletRepo.updateBalance(walletId, wallet.balance());
  }
  
  public void transfer(Long fromWalletId, Long toWalletId, BigDecimal amount) {
    //...跟基于贫血模型的传统开发模式的代码一样...
  }
}

可以看到Domain中也实现了几个业务判定
整体在Service中也调用了domain中的几个方法

如果业务更加复杂

public class VirtualWallet {
  private Long id;
  private Long createTime = System.currentTimeMillis();;
  private BigDecimal balance = BigDecimal.ZERO;
  private boolean isAllowedOverdraft = true;
  private BigDecimal overdraftAmount = BigDecimal.ZERO;
  private BigDecimal frozenAmount = BigDecimal.ZERO;
  
  public VirtualWallet(Long preAllocatedId) {
    this.id = preAllocatedId;
  }
  
  public void freeze(BigDecimal amount) { ... }
  public void unfreeze(BigDecimal amount) { ...}
  public void increaseOverdraftAmount(BigDecimal amount) { ... }
  public void decreaseOverdraftAmount(BigDecimal amount) { ... }
  public void closeOverdraft() { ... }
  public void openOverdraft() { ... }
  
  public BigDecimal balance() {
    return this.balance;
  }
  
  public BigDecimal getAvailableBalance() {
    BigDecimal totalAvaliableBalance = this.balance.subtract(this.frozenAmount);
    if (isAllowedOverdraft) {
      totalAvaliableBalance += this.overdraftAmount;
    }
    return totalAvaliableBalance;
  }
  
  public void debit(BigDecimal amount) {
    BigDecimal totalAvaliableBalance = getAvailableBalance();
    if (totoalAvaliableBalance.compareTo(amount) < 0) {
      throw new InsufficientBalanceException(...);
    }
    this.balance.subtract(amount);
  }
  
  public void credit(BigDecimal amount) {
    if (amount.compareTo(BigDecimal.ZERO) < 0) {
      throw new InvalidAmountException(...);
    }
    this.balance.add(amount);
  }
}

更复杂的业务在Domain中得到解决，实际repo或dao还会在service中进行
Domain中保留独立性 与其他服务层解耦