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詳解基于Spring Data的領(lǐng)域事件發(fā)布

更新時(shí)間：2020年04月02日 09:22:04 作者：barry的異想世界

這篇文章主要介紹了詳解基于Spring Data的領(lǐng)域事件發(fā)布，文中通過示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，需要的朋友們下面隨著小編來一起學(xué)習(xí)學(xué)習(xí)吧

領(lǐng)域事件發(fā)布是一個(gè)領(lǐng)域?qū)ο鬄榱俗屍渌鼘?duì)象知道自己已經(jīng)處理完成某個(gè)操作時(shí)發(fā)出的一個(gè)通知，事件發(fā)布力求從代碼層面讓自身對(duì)象與外部對(duì)象解耦，并減少技術(shù)代碼入侵。

一、手動(dòng)發(fā)布事件

// 實(shí)體定義
@Entity
public class Department implements Serializable {
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Integer departmentId;

  @Enumerated(EnumType.STRING)
  private State state;
}

// 事件定義
public class DepartmentEvent {
  private Department department;
  private State state;
  public DepartmentEvent(Department department) {
    this.department = department;
    state = department.getState();
  }
}

// 領(lǐng)域服務(wù)
@Service
public class ApplicationService {

  @Autowired
  private ApplicationEventPublisher applicationEventPublisher;

  @Autowired
  private DepartmentRepository departmentRepository;

  @Transactional(rollbackFor = Exception.class)
  public void departmentAdd(Department department) {
    departmentRepository.save(department);
    // 事件發(fā)布
    applicationEventPublisher.publishEvent(new DepartmentEvent(department));
  }
}

使用applicationEventPublisher.publishEvent在領(lǐng)域服務(wù)處理完成后發(fā)布領(lǐng)域事件，此方法需要在業(yè)務(wù)代碼中顯式發(fā)布事件，并在領(lǐng)域服務(wù)里引入ApplicationEventPublisher類，但對(duì)領(lǐng)域服務(wù)本身有一定的入侵性，但靈活性較高。

二、自動(dòng)發(fā)布事件

// 實(shí)體定義
@Entity
public class SaleOrder implements Serializable {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Integer orderId;
  
  @Enumerated(EnumType.STRING)
  private State state;

  // 返回類型定義
  @DomainEvents
  public List<Object> domainEvents(){
    return Stream.of(new SaleOrderEvent(this)).collect(Collectors.toList());
  }

  // 事件發(fā)布后callback
  @AfterDomainEventPublication
  void callback() {
    System.err.println("ok");
  }
}

// 事件定義
public class SaleOrderEvent {
  private SaleOrder saleOrder;
  private State state;
  public SaleOrderEvent(SaleOrder saleOrder) {
    this.saleOrder = saleOrder;
    state = saleOrder.getState();
  }
}

// 領(lǐng)域服務(wù)
@Service
public class ApplicationService {
  @Autowired
  private OrderRepository orderRepository;
  
  @Transactional(rollbackFor = Exception.class)
  public void saleOrderAdd(SaleOrder saleOrder) {
    orderRepository.save(saleOrder);
  }
}

使用@DomainEvents定義事件返回的類型，必須是一個(gè)集合，使用@AfterDomainEventPublication定義事件發(fā)布后的回調(diào)。

此方法實(shí)事件類型定義在實(shí)體中，與領(lǐng)域服務(wù)完全解耦，沒有入侵。系統(tǒng)會(huì)在orderRepository.save(saleOrder)后自動(dòng)調(diào)用事件發(fā)布，另delete方法不會(huì)調(diào)用事件發(fā)布。

三、事件監(jiān)聽

@Component
public class ApplicationEventProcessor {

  @EventListener(condition = "#departmentEvent.getState().toString() == 'SUCCEED'")
  public void departmentCreated(DepartmentEvent departmentEvent) {
    System.err.println("dept-event1:" + departmentEvent);
  }

  @Async
  @TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT, condition = "#saleOrderEvent.getState().toString() == 'SUCCEED'")
  public void saleOrderCreated(SaleOrderEvent saleOrderEvent) {
    System.err.println("sale-event succeed1:" + saleOrderEvent);
  }

  @TransactionalEventListener(phase = TransactionPhase.BEFORE_COMMIT, condition = "#saleOrderEvent.getState().toString() == 'SUCCEED'")
  public void saleOrderCreatedBefore(SaleOrderEvent saleOrderEvent) {
    System.err.println("sale-event succeed2:" + saleOrderEvent);
  }

  @Async
  @TransactionalEventListener(phase = TransactionPhase.AFTER_ROLLBACK)
  public void saleOrderCreatedFailed(SaleOrderEvent saleOrderEvent) {
    System.out.println("sale-event failed:" + saleOrderEvent);
  }
}

1. 使用@EventListener監(jiān)聽事件

@EventListener沒有事務(wù)支持，只要事件發(fā)出就可監(jiān)控到

@Transactional(rollbackFor = Exception.class)
public void departmentAdd(Department department) {
  departmentRepository.save(department);
  applicationEventPublisher.publishEvent(new DepartmentEvent(department));
  throw new RuntimeException("failed");
}

上述情況會(huì)造成事務(wù)失敗回滾，但事件監(jiān)控端已經(jīng)執(zhí)行，可能導(dǎo)致數(shù)據(jù)不一致的情況發(fā)生

2. 使用@TransactionalEventListener監(jiān)聽事件

TransactionPhase.BEFORE_COMMIT 事務(wù)提交前
TransactionPhase.AFTER_COMMIT 事務(wù)提交后
TransactionPhase.AFTER_ROLLBACK 事務(wù)回滾后
TransactionPhase.AFTER_COMPLETION 事務(wù)完成后

使用TransactionPhase.AFTER_COMMIT可在事務(wù)完成后，再執(zhí)行事件監(jiān)聽方法，從而保證數(shù)據(jù)的一致性

3. TransactionPhase.AFTER_ROLLBACK回滾事務(wù)問題

@Async
@TransactionalEventListener(phase = TransactionPhase.AFTER_ROLLBACK, condition = "#departmentEvent.getState().toString() == 'SUCCEED'")
public void departmentCreatedFailed(DepartmentEvent departmentEvent) {
  System.err.println("dept-event3:" + departmentEvent);
}

由于@DomainEvents作用在實(shí)體上的，只有剛orderRepository.save(saleOrder)執(zhí)行成功后才會(huì)發(fā)送事件，故AFTER_ROLLBACK方法只會(huì)在同一事務(wù)中其它語句執(zhí)行失敗或顯式rollback時(shí)才會(huì)執(zhí)行，如果save方法執(zhí)行失敗，將不會(huì)監(jiān)聽到回滾事件。

4. @Async異步事件監(jiān)聽