猫头鹰的深夜翻译：设计模式EventBus

/**
 * interface describing a generic event, and it's associated meta data, it's this what's going to
 * get sent in the bus to be dispatched to intrested Subscribers
 *
 * @author chermehdi
 */
public interface Event<T> {
  /**
   * @returns the stored data associated with the event
   */
  T getData();
}

import java.util.Set;
/**
 * Description of a generic subscriber
 *
 * @author chermehdi
 */
public interface Subscribable {
  /**
   * Consume the events dispatched by the bus, events passed as parameter are can only be of type
   * declared by the supports() Set
   */
  void handle(Event<?> event);
  /**
   * describes the set of classes the subscribable object intends to handle
   */
  
  Set<Class<?>> supports();
}

import java.util.List;
/**
 * Description of the contract of a generic EventBus implementation, the library contains two main
 * version, Sync and Async event bus implementations, if you want to provide your own implementation
 * and stay compliant with the components of the library just implement this contract
 *
 * @author chermehdi
 */
public interface EventBus {
  /**
   * registers a new subscribable to this EventBus instance
   */
  void register(Subscribable subscribable);
  /**
   * send the given event in this EventBus implementation to be consumed by interested subscribers
   */
  void dispatch(Event<?> event);
  /**
   * get the list of all the subscribers associated with this EventBus instance
   */
  List<Subscribable> getSubscribers();
}

import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Vector;
import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.Collectors;
/**
 * Simple implementation demonstrating how a guava EventBus works generally, without all the noise
 * of special cases handling, and special guava collections
 *
 * @author chermehdi
 */
public class EventBus {
  private Map<Class<?>, List<Invocation>> invocations;
  private String name;
  public EventBus(String name) {
    this.name = name;
    invocations = new ConcurrentHashMap<>();
  }
  public void post(Object object) {
    Class<?> clazz = object.getClass();
    if (invocations.containsKey(clazz)) {
      invocations.get(clazz).forEach(invocation -> invocation.invoke(object));
    }
  }
  public void register(Object object) {
    Class<?> currentClass = object.getClass();
    // we try to navigate the object tree back to object ot see if
    // there is any annotated @Subscribe classes
    while (currentClass != null) {
      List<Method> subscribeMethods = findSubscriptionMethods(currentClass);
      for (Method method : subscribeMethods) {
        // we know for sure that it has only one parameter
        Class<?> type = method.getParameterTypes()[0];
        if (invocations.containsKey(type)) {
          invocations.get(type).add(new Invocation(method, object));
        } else {
          List<Invocation> temp = new Vector<>();
          temp.add(new Invocation(method, object));
          invocations.put(type, temp);
        }
      }
      currentClass = currentClass.getSuperclass();
    }
  }
  private List<Method> findSubscriptionMethods(Class<?> type) {
    List<Method> subscribeMethods = Arrays.stream(type.getDeclaredMethods())
        .filter(method -> method.isAnnotationPresent(Subscribe.class))
        .collect(Collectors.toList());
    checkSubscriberMethods(subscribeMethods);
    return subscribeMethods;
  }
  private void checkSubscriberMethods(List<Method> subscribeMethods) {
    boolean hasMoreThanOneParameter = subscribeMethods.stream()
        .anyMatch(method -> method.getParameterCount() != 1);
    if (hasMoreThanOneParameter) {
      throw new IllegalArgumentException(
          "Method annotated with @Susbscribe has more than one parameter");
    }
  }
  public Map<Class<?>, List<Invocation>> getInvocations() {
    return invocations;
  }
  public String getName() {
    return name;
  }
}