设计模式之美 Part2

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 virtualWalletRepo.getBalance(walletId);
  }

  public void debit(Long walletId, BigDecimal amount) {
    VirtualWalletEntity walletEntity = walletRepo.getWalletEntity(walletId);

    // 贫血型
    // BigDecimal balance = walletEntity.getBalance();
    // if (balance.compareTo(amount) < 0) {
    //   throw new NoSufficientBalanceException(...);
    // }
    // walletRepo.updateBalance(walletId, balance.subtract(amount));

    // DDD
    VirtualWallet wallet = convert(walletEntity);
    wallet.debit(amount);
    walletRepo.updateBalance(walletId, wallet.balance());
  }

  public void credit(Long walletId, BigDecimal amount) {
    VirtualWalletEntity walletEntity = walletRepo.getWalletEntity(walletId);

    // 贫血型
    // BigDecimal balance = walletEntity.getBalance();
    // walletRepo.updateBalance(walletId, balance.add(amount));

    // DDD
    VirtualWallet wallet = convert(walletEntity);
    wallet.credit(amount);
    walletRepo.updateBalance(walletId, wallet.balance());
  }

  public void transfer(Long fromWalletId, Long toWalletId, BigDecimal amount) {
    VirtualWalletTransactionEntity transactionEntity = new VirtualWalletTransactionEntity();
    transactionEntity.setAmount(amount);
    transactionEntity.setCreateTime(System.currentTimeMillis());
    transactionEntity.setFromWalletId(fromWalletId);
    transactionEntity.setToWalletId(toWalletId);
    transactionEntity.setStatus(Status.TO_BE_EXECUTED);
    Long transactionId = transactionRepo.saveTransaction(transactionEntity);
    try {
      debit(fromWalletId, amount);
      credit(toWalletId, amount);
    } catch (InsufficientBalanceException e) {
      transactionRepo.updateStatus(transactionId, Status.CLOSED);
      // ...rethrow exception e...
    } catch (Exception e) {
      transactionRepo.updateStatus(transactionId, Status.FAILED);
      // ...rethrow exception e...
    }
    transactionRepo.updateStatus(transactionId, Status.EXECUTED);
  }
}

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 BigDecimal balance() {
    return this.balance;
  }

  public BigDecimal getAvaliableBalance() {
    BigDecimal totalAvaliableBalance = this.balance.subtract(this.frozenAmount);
    if (isAllowedOverdraft) {
      totalAvaliableBalance += this.overdraftAmount;
    }
    return totalAvaliableBalance;
  }

  public void debit(BigDecimal amount) {}
  public void credit(BigDecimal amount) {}

  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() { ... }
}