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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
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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.
*/
package com.google.common.eventbus;
import com.google.common.base.Throwables;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Multimap;
import com.google.common.reflect.TypeToken;
import com.google.common.util.concurrent.UncheckedExecutionException;
import java.lang.reflect.Method;
import java.util.Set;
/**
* A {@link HandlerFindingStrategy} for collecting all event handler methods that are marked with
* the {@link Subscribe} annotation.
*
* @author Cliff Biffle
* @author Louis Wasserman
*/
class AnnotatedHandlerFinder implements HandlerFindingStrategy {
/**
* A thread-safe cache that contains the mapping from each class to all methods in that class and
* all super-classes, that are annotated with {@code @Subscribe}. The cache is shared across all
* instances of this class; this greatly improves performance if multiple EventBus instances are
* created and objects of the same class are registered on all of them.
*/
private static final LoadingCache<Class<?>, ImmutableList<Method>> handlerMethodsCache =
CacheBuilder.newBuilder()
.weakKeys()
.build(new CacheLoader<Class<?>, ImmutableList<Method>>() {
@Override
public ImmutableList<Method> load(Class<?> concreteClass) throws Exception {
return getAnnotatedMethodsInternal(concreteClass);
}
});
/**
* {@inheritDoc}
*
* This implementation finds all methods marked with a {@link Subscribe} annotation.
*/
@Override
public Multimap<Class<?>, EventHandler> findAllHandlers(Object listener) {
Multimap<Class<?>, EventHandler> methodsInListener = HashMultimap.create();
Class<?> clazz = listener.getClass();
for (Method method : getAnnotatedMethods(clazz)) {
Class<?>[] parameterTypes = method.getParameterTypes();
Class<?> eventType = parameterTypes[0];
EventHandler handler = makeHandler(listener, method);
methodsInListener.put(eventType, handler);
}
return methodsInListener;
}
private static ImmutableList<Method> getAnnotatedMethods(Class<?> clazz) {
try {
return handlerMethodsCache.getUnchecked(clazz);
} catch (UncheckedExecutionException e) {
throw Throwables.propagate(e.getCause());
}
}
private static ImmutableList<Method> getAnnotatedMethodsInternal(Class<?> clazz) {
Set<? extends Class<?>> supers = TypeToken.of(clazz).getTypes().rawTypes();
ImmutableList.Builder<Method> result = ImmutableList.builder();
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];
result.add(method);
break;
}
} catch (NoSuchMethodException ignored) {
// Move on.
}
}
}
return result.build();
}
/**
* Creates an {@code EventHandler} for subsequently calling {@code method} on
* {@code listener}.
* Selects an EventHandler implementation based on the annotations on
* {@code method}.
*
* @param listener object bearing the event handler method.
* @param method the event handler method to wrap in an EventHandler.
* @return an EventHandler that will call {@code method} on {@code listener}
* when invoked.
*/
private static EventHandler makeHandler(Object listener, Method method) {
EventHandler wrapper;
if (methodIsDeclaredThreadSafe(method)) {
wrapper = new EventHandler(listener, method);
} else {
wrapper = new SynchronizedEventHandler(listener, method);
}
return wrapper;
}
/**
* Checks whether {@code method} is thread-safe, as indicated by the
* {@link AllowConcurrentEvents} annotation.
*
* @param method handler method to check.
* @return {@code true} if {@code handler} is marked as thread-safe,
* {@code false} otherwise.
*/
private static boolean methodIsDeclaredThreadSafe(Method method) {
return method.getAnnotation(AllowConcurrentEvents.class) != null;
}
}
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