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   * Copyright (C) 2007 The Guava Authors
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
 import java.util.Set;

A HandlerFindingStrategy for collecting all event handler methods that are marked with the Subscribe annotation.

Cliff Biffle
Louis Wasserman
This implementation finds all methods marked with a Subscribe annotation.
   public Multimap<Class<?>, EventHandlerfindAllHandlers(Object listener) {
     Multimap<Class<?>, EventHandlermethodsInListener = HashMultimap.create();
     Class<?> clazz = listener.getClass();
     Set<? extends Class<?>> supers = TypeToken.of(clazz).getTypes().rawTypes();
     for (Method method : clazz.getMethods()) {
        * Iterate over each distinct method of {@code clazz}, checking if it is annotated with
        * @Subscribe by any of the superclasses or superinterfaces that declare it.
       for (Class<?> c : supers) {
         try {
           Method m = c.getMethod(method.getName(), method.getParameterTypes());
           if (m.isAnnotationPresent(Subscribe.class)) {
             Class<?>[] parameterTypes = method.getParameterTypes();
             if (parameterTypes.length != 1) {
               throw new IllegalArgumentException("Method " + method
                   + " has @Subscribe annotation, but requires " + parameterTypes.length
                   + " arguments.  Event handler methods must require a single argument.");
             Class<?> eventType = parameterTypes[0];
             EventHandler handler = makeHandler(listenermethod);
         } catch (NoSuchMethodException ignored) {
           // Move on.
     return methodsInListener;

Creates an EventHandler for subsequently calling method on listener. Selects an EventHandler implementation based on the annotations on method.

listener object bearing the event handler method.
method the event handler method to wrap in an EventHandler.
an EventHandler that will call method on listener when invoked.
   private static EventHandler makeHandler(Object listenerMethod method) {
     EventHandler wrapper;
     if (methodIsDeclaredThreadSafe(method)) {
       wrapper = new EventHandler(listenermethod);
     } else {
       wrapper = new SynchronizedEventHandler(listenermethod);
     return wrapper;

Checks whether method is thread-safe, as indicated by the AllowConcurrentEvents annotation.

method handler method to check.
true if handler is marked as thread-safe, false otherwise.
  private static boolean methodIsDeclaredThreadSafe(Method method) {
    return method.getAnnotation(AllowConcurrentEvents.class) != null;
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