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本文主要賞析一下buckpal對於Hexagonal Architecture的實踐
項目結構
├── adapter
│ ├── in
│ │ └── web
│ │ └── SendMoneyController.java
│ └── out
│ └── persistence
│ ├── AccountJpaEntity.java
│ ├── AccountMapper.java
│ ├── AccountPersistenceAdapter.java
│ ├── ActivityJpaEntity.java
│ ├── ActivityRepository.java
│ └── SpringDataAccountRepository.java
├── application
│ ├── port
│ │ ├── in
│ │ │ ├── GetAccountBalanceQuery.java
│ │ │ ├── SendMoneyCommand.java
│ │ │ └── SendMoneyUseCase.java
│ │ └── out
│ │ ├── AccountLock.java
│ │ ├── LoadAccountPort.java
│ │ └── UpdateAccountStatePort.java
│ └── service
│ ├── GetAccountBalanceService.java
│ ├── MoneyTransferProperties.java
│ ├── NoOpAccountLock.java
│ ├── SendMoneyService.java
│ └── ThresholdExceededException.java
└── domain
├── Account.java
├── Activity.java
├── ActivityWindow.java
└── Money.java
這裏分爲adapter、application、domain三層；其中application層定義了port包，該包定義了in、out兩種類型的接口；adapter層也分in、out兩類，分別實現application/port層的接口；application的service則實現了port的接口
application/port
in
public interface GetAccountBalanceQuery {
Money getAccountBalance(AccountId accountId);
}
@Value
@EqualsAndHashCode(callSuper = false)
public
class SendMoneyCommand extends SelfValidating<SendMoneyCommand> {
@NotNull
private final AccountId sourceAccountId;
@NotNull
private final AccountId targetAccountId;
@NotNull
private final Money money;
public SendMoneyCommand(
AccountId sourceAccountId,
AccountId targetAccountId,
Money money) {
this.sourceAccountId = sourceAccountId;
this.targetAccountId = targetAccountId;
this.money = money;
this.validateSelf();
}
}
public interface SendMoneyUseCase {
boolean sendMoney(SendMoneyCommand command);
}
application/port/in定義了GetAccountBalanceQuery、SendMoneyUseCase接口
out
public interface AccountLock {
void lockAccount(Account.AccountId accountId);
void releaseAccount(Account.AccountId accountId);
}
public interface LoadAccountPort {
Account loadAccount(AccountId accountId, LocalDateTime baselineDate);
}
public interface UpdateAccountStatePort {
void updateActivities(Account account);
}
application/port/out定義了AccountLock、LoadAccountPort、UpdateAccountStatePort接口
application/service
@RequiredArgsConstructor
class GetAccountBalanceService implements GetAccountBalanceQuery {
private final LoadAccountPort loadAccountPort;
@Override
public Money getAccountBalance(AccountId accountId) {
return loadAccountPort.loadAccount(accountId, LocalDateTime.now())
.calculateBalance();
}
}
@Component
class NoOpAccountLock implements AccountLock {
@Override
public void lockAccount(AccountId accountId) {
// do nothing
}
@Override
public void releaseAccount(AccountId accountId) {
// do nothing
}
}
@RequiredArgsConstructor
@UseCase
@Transactional
public class SendMoneyService implements SendMoneyUseCase {
private final LoadAccountPort loadAccountPort;
private final AccountLock accountLock;
private final UpdateAccountStatePort updateAccountStatePort;
private final MoneyTransferProperties moneyTransferProperties;
@Override
public boolean sendMoney(SendMoneyCommand command) {
checkThreshold(command);
LocalDateTime baselineDate = LocalDateTime.now().minusDays(10);
Account sourceAccount = loadAccountPort.loadAccount(
command.getSourceAccountId(),
baselineDate);
Account targetAccount = loadAccountPort.loadAccount(
command.getTargetAccountId(),
baselineDate);
AccountId sourceAccountId = sourceAccount.getId()
.orElseThrow(() -> new IllegalStateException("expected source account ID not to be empty"));
AccountId targetAccountId = targetAccount.getId()
.orElseThrow(() -> new IllegalStateException("expected target account ID not to be empty"));
accountLock.lockAccount(sourceAccountId);
if (!sourceAccount.withdraw(command.getMoney(), targetAccountId)) {
accountLock.releaseAccount(sourceAccountId);
return false;
}
accountLock.lockAccount(targetAccountId);
if (!targetAccount.deposit(command.getMoney(), sourceAccountId)) {
accountLock.releaseAccount(sourceAccountId);
accountLock.releaseAccount(targetAccountId);
return false;
}
updateAccountStatePort.updateActivities(sourceAccount);
updateAccountStatePort.updateActivities(targetAccount);
accountLock.releaseAccount(sourceAccountId);
accountLock.releaseAccount(targetAccountId);
return true;
}
private void checkThreshold(SendMoneyCommand command) {
if(command.getMoney().isGreaterThan(moneyTransferProperties.getMaximumTransferThreshold())){
throw new ThresholdExceededException(moneyTransferProperties.getMaximumTransferThreshold(), command.getMoney());
}
}
}
application/service的GetAccountBalanceService實現了application.port.in.GetAccountBalanceQuery接口；NoOpAccountLock實現了application.port.out.AccountLock接口；SendMoneyService實現了application.port.in.SendMoneyUseCase接口
domain
@AllArgsConstructor(access = AccessLevel.PRIVATE)
public class Account {
/**
* The unique ID of the account.
*/
@Getter private final AccountId id;
/**
* The baseline balance of the account. This was the balance of the account before the first
* activity in the activityWindow.
*/
@Getter private final Money baselineBalance;
/**
* The window of latest activities on this account.
*/
@Getter private final ActivityWindow activityWindow;
/**
* Creates an {@link Account} entity without an ID. Use to create a new entity that is not yet
* persisted.
*/
public static Account withoutId(
Money baselineBalance,
ActivityWindow activityWindow) {
return new Account(null, baselineBalance, activityWindow);
}
/**
* Creates an {@link Account} entity with an ID. Use to reconstitute a persisted entity.
*/
public static Account withId(
AccountId accountId,
Money baselineBalance,
ActivityWindow activityWindow) {
return new Account(accountId, baselineBalance, activityWindow);
}
public Optional<AccountId> getId(){
return Optional.ofNullable(this.id);
}
/**
* Calculates the total balance of the account by adding the activity values to the baseline balance.
*/
public Money calculateBalance() {
return Money.add(
this.baselineBalance,
this.activityWindow.calculateBalance(this.id));
}
/**
* Tries to withdraw a certain amount of money from this account.
* If successful, creates a new activity with a negative value.
* @return true if the withdrawal was successful, false if not.
*/
public boolean withdraw(Money money, AccountId targetAccountId) {
if (!mayWithdraw(money)) {
return false;
}
Activity withdrawal = new Activity(
this.id,
this.id,
targetAccountId,
LocalDateTime.now(),
money);
this.activityWindow.addActivity(withdrawal);
return true;
}
private boolean mayWithdraw(Money money) {
return Money.add(
this.calculateBalance(),
money.negate())
.isPositiveOrZero();
}
/**
* Tries to deposit a certain amount of money to this account.
* If sucessful, creates a new activity with a positive value.
* @return true if the deposit was successful, false if not.
*/
public boolean deposit(Money money, AccountId sourceAccountId) {
Activity deposit = new Activity(
this.id,
sourceAccountId,
this.id,
LocalDateTime.now(),
money);
this.activityWindow.addActivity(deposit);
return true;
}
@Value
public static class AccountId {
private Long value;
}
}
public class ActivityWindow {
/**
* The list of account activities within this window.
*/
private List<Activity> activities;
/**
* The timestamp of the first activity within this window.
*/
public LocalDateTime getStartTimestamp() {
return activities.stream()
.min(Comparator.comparing(Activity::getTimestamp))
.orElseThrow(IllegalStateException::new)
.getTimestamp();
}
/**
* The timestamp of the last activity within this window.
* @return
*/
public LocalDateTime getEndTimestamp() {
return activities.stream()
.max(Comparator.comparing(Activity::getTimestamp))
.orElseThrow(IllegalStateException::new)
.getTimestamp();
}
/**
* Calculates the balance by summing up the values of all activities within this window.
*/
public Money calculateBalance(AccountId accountId) {
Money depositBalance = activities.stream()
.filter(a -> a.getTargetAccountId().equals(accountId))
.map(Activity::getMoney)
.reduce(Money.ZERO, Money::add);
Money withdrawalBalance = activities.stream()
.filter(a -> a.getSourceAccountId().equals(accountId))
.map(Activity::getMoney)
.reduce(Money.ZERO, Money::add);
return Money.add(depositBalance, withdrawalBalance.negate());
}
public ActivityWindow(@NonNull List<Activity> activities) {
this.activities = activities;
}
public ActivityWindow(@NonNull Activity... activities) {
this.activities = new ArrayList<>(Arrays.asList(activities));
}
public List<Activity> getActivities() {
return Collections.unmodifiableList(this.activities);
}
public void addActivity(Activity activity) {
this.activities.add(activity);
}
}
Account類定義了calculateBalance、withdraw、deposit方法；ActivityWindow類定義了calculateBalance方法
小結
buckpal工程adapter、application、domain三層；其中application層定義了port包，該包定義了in、out兩種類型的接口；adapter層也分in、out兩類，分別實現application/port層的接口；application的service則實現了port的接口。其中domain層不依賴任何層；application層的port定義了接口，然後service層實現接口和引用接口；adapter層則實現了application的port層的接口。