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)象解耦氯材，并減少技術(shù)代碼入侵荣挨。
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)域事件莉掂，此方法需要在業(yè)務(wù)代碼中顯式發(fā)布事件葛圃，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憎妙，但靈活性較高库正。
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厘唾，必須是一個(gè)集合褥符，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)體中抚垃，與領(lǐng)域服務(wù)完全解耦喷楣，沒(méi)有入侵趟大。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)布抡蛙。
三、 事件監(jiān)聽(tīng)
@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(tīng)事件
@EventListener沒(méi)有事務(wù)支持魂迄，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)失敗回滾粗截，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(tīng)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)完成后捣炬，再執(zhí)行事件監(jiān)聽(tīng)方法熊昌，從而保證數(shù)據(jù)的一致性
3. TransactionPhase.AFTER_ROLLBACK回滾事務(wù)問(wèn)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)送事件湿酸，故AFTER_ROLLBACK方法只會(huì)在同一事務(wù)中其它語(yǔ)句執(zhí)行失敗或顯式rollback時(shí)才會(huì)執(zhí)行婿屹，如果save方法執(zhí)行失敗，將不會(huì)監(jiān)聽(tīng)到回滾事件推溃。
4. @Async異步事件監(jiān)聽(tīng)
- 沒(méi)有此注解事件監(jiān)聽(tīng)方法與主方法為一個(gè)事務(wù)昂利。
- 使用此注解將脫離原有事務(wù)，BEFORE_COMMIT也無(wú)法攔截事務(wù)提交前時(shí)刻
- 此注解需要配合
@EnableAsync一起使用
四铁坎、 總結(jié)
通過(guò)對(duì) @DomainEvents蜂奸、@TransactionalEventListener的使用，在有效的解決領(lǐng)域事件發(fā)布的情況下硬萍，減少了對(duì)業(yè)務(wù)代碼的入侵扩所，同時(shí)盡一步解決了數(shù)據(jù)一致性問(wèn)題。
在分布式結(jié)構(gòu)下朴乖，通過(guò)MQ發(fā)送事件通知給其它服務(wù)祖屏，為解決一致性問(wèn)題，防止對(duì)方服務(wù)處理失敗可先將事件保久化到數(shù)據(jù)庫(kù)后买羞，再重試袁勺。
五、 源碼
https://gitee.com/hypier/barry-jpa/tree/master/jpa-section-5
