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本文次要钻研一下event-sourcing-cqrs的model
Event
public abstract class Event { private final UUID aggregateId; private final ZonedDateTime timestamp; private final int version; protected Event(UUID aggregateId, ZonedDateTime timestamp, int version) { this.aggregateId = checkNotNull(aggregateId); this.timestamp = checkNotNull(timestamp); this.version = version; } public UUID getAggregateId() { return aggregateId; } public ZonedDateTime getTimestamp() { return this.timestamp; } public int getVersion() { return version; }}Event定义了aggregateId、timestamp、version属性
EventStore
public interface EventStore { void store(UUID aggregateId, List<Event> newEvents, int baseVersion) throws OptimisticLockingException; List<Event> load(UUID aggregateId);}EventStore接口定义了store、load办法
Aggregate
public abstract class Aggregate { private UUID id; private int baseVersion; private List<Event> newEvents; protected Aggregate(UUID id) { this(id, emptyList()); } protected Aggregate(UUID id, List<Event> eventStream) { checkNotNull(id); checkNotNull(eventStream); this.id = id; eventStream.forEach(e -> { apply(e); this.baseVersion = e.getVersion(); }); this.newEvents = new ArrayList<>(); } protected void applyNewEvent(Event event) { checkArgument(event.getVersion() == getNextVersion(), "New event version '%s' does not match expected next version '%s'", event.getVersion(), getNextVersion()); apply(event); newEvents.add(event); } private void apply(Event event) { try { Method method = this.getClass().getDeclaredMethod("apply", event.getClass()); method.setAccessible(true); method.invoke(this, event); } catch (InvocationTargetException e) { Throwables.propagate(e.getCause()); } catch (NoSuchMethodException | IllegalAccessException e) { throw new UnsupportedOperationException( format("Aggregate '%s' doesn't apply event type '%s'", this.getClass(), event.getClass()), e); } } public UUID getId() { return id; } public int getBaseVersion() { return baseVersion; } public List<Event> getNewEvents() { return ImmutableList.copyOf(newEvents); } protected int getNextVersion() { return baseVersion + newEvents.size() + 1; }}Aggregate定义了id、baseVersion、newEvents属性；其applyNewEvent办法会执行apply(event)及newEvents.add(event)；apply办法通过反射执行event的apply办法
ValueObject
public abstract class ValueObject { @Override public boolean equals(Object o) { return EqualsBuilder.reflectionEquals(this, o); } @Override public int hashCode() { return HashCodeBuilder.reflectionHashCode(this); } @Override public String toString() { return ToStringBuilder.reflectionToString(this, ToStringStyle.SHORT_PREFIX_STYLE); }}ValueObject笼罩了equals、hashCode、toString办法
Specification
public interface Specification<T> { boolean isSatisfiedBy(T value);}Specification接口定义了isSatisfiedBy办法
小结
event-sourcing-cqrs-examples的model定义了Event、Aggregate、ValueObject抽象类以及EventStore、Specification接口。
doc
- event-sourcing-cqrs-examples