Use custom AnnotatedHandlerFinder and pretend all events are thread safe

api/src/main/java/com/google/common/eventbus/AnnotatedHandlerFinder.java

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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 = new EventHandler(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();
+  }
+}