com.ovea.tajin.framework.async.guava.AnnotatedHandlerFinder.groovy Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of tajin-async Show documentation
The newest version!
/*
 * 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.ovea.tajin.framework.async.guava

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.eventbus.AllowConcurrentEvents
import com.google.common.eventbus.Subscribe
import com.google.common.reflect.TypeToken
import com.google.common.util.concurrent.UncheckedExecutionException

import java.lang.reflect.Method

/**
 * A {@link HandlerFindingStrategy} for collecting all event handler methods that are marked with
 * the {@link com.google.common.eventbus.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, ImmutableList> handlerMethodsCache =
        CacheBuilder.newBuilder()
            .weakKeys()
            .build(new CacheLoader, ImmutableList>() {
            @Override
            public ImmutableList load(Class concreteClass) throws Exception {
                return getAnnotatedMethodsInternal(concreteClass);
            }
        });

    /**
     * {@inheritDoc}
     *
     * This implementation finds all methods marked with a {@link com.google.common.eventbus.Subscribe} annotation.
     */
    @Override
    public Multimap, EventHandler> findAllHandlers(Object listener) {
        Multimap, 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 getAnnotatedMethods(Class clazz) {
        try {
            return handlerMethodsCache.getUnchecked(clazz);
        } catch (UncheckedExecutionException e) {
            throw Throwables.propagate(e.getCause());
        }
    }

    private static ImmutableList getAnnotatedMethodsInternal(Class clazz) {
        Set> supers = TypeToken.of(clazz).getTypes().rawTypes();
        ImmutableList.Builder 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 com.google.common.eventbus.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;
    }
}