/*
* Copyright 2002-2019 the original author or 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
*
* https://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 org.springframework.context.event;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import org.springframework.aop.framework.AopProxyUtils;
import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.core.ResolvableType;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;
/**
* Abstract implementation of the {@link ApplicationEventMulticaster} interface,
* providing the basic listener registration facility.
*
* <p>Doesn't permit multiple instances of the same listener by default,
* as it keeps listeners in a linked Set. The collection class used to hold
* ApplicationListener objects can be overridden through the "collectionClass"
* bean property.
*
* <p>Implementing ApplicationEventMulticaster's actual {@link #multicastEvent} method
* is left to subclasses. {@link SimpleApplicationEventMulticaster} simply multicasts
* all events to all registered listeners, invoking them in the calling thread.
* Alternative implementations could be more sophisticated in those respects.
*
* @author Juergen Hoeller
* @author Stephane Nicoll
* @since 1.2.3
* @see #getApplicationListeners(ApplicationEvent, ResolvableType)
* @see SimpleApplicationEventMulticaster
*/
public abstract class AbstractApplicationEventMulticaster
implements ApplicationEventMulticaster, BeanClassLoaderAware, BeanFactoryAware {
private final ListenerRetriever defaultRetriever = new ListenerRetriever(false);
final Map<ListenerCacheKey, ListenerRetriever> retrieverCache = new ConcurrentHashMap<>(64);
@Nullable
private ClassLoader beanClassLoader;
@Nullable
private BeanFactory beanFactory;
private Object retrievalMutex = this.defaultRetriever;
@Override
public void setBeanClassLoader(ClassLoader classLoader) {
this.beanClassLoader = classLoader;
}
@Override
public void setBeanFactory(BeanFactory beanFactory) {
this.beanFactory = beanFactory;
if (beanFactory instanceof ConfigurableBeanFactory) {
ConfigurableBeanFactory cbf = (ConfigurableBeanFactory) beanFactory;
if (this.beanClassLoader == null) {
this.beanClassLoader = cbf.getBeanClassLoader();
}
this.retrievalMutex = cbf.getSingletonMutex();
}
}
private BeanFactory getBeanFactory() {
if (this.beanFactory == null) {
throw new IllegalStateException("ApplicationEventMulticaster cannot retrieve listener beans " +
"because it is not associated with a BeanFactory");
}
return this.beanFactory;
}
@Override
public void addApplicationListener(ApplicationListener<?> listener) {
synchronized (this.retrievalMutex) {
// Explicitly remove target for a proxy, if registered already,
// in order to avoid double invocations of the same listener.
Object singletonTarget = AopProxyUtils.getSingletonTarget(listener);
if (singletonTarget instanceof ApplicationListener) {
this.defaultRetriever.applicationListeners.remove(singletonTarget);
}
this.defaultRetriever.applicationListeners.add(listener);
this.retrieverCache.clear();
}
}
@Override
public void addApplicationListenerBean(String listenerBeanName) {
synchronized (this.retrievalMutex) {
this.defaultRetriever.applicationListenerBeans.add(listenerBeanName);
this.retrieverCache.clear();
}
}
@Override
public void removeApplicationListener(ApplicationListener<?> listener) {
synchronized (this.retrievalMutex) {
this.defaultRetriever.applicationListeners.remove(listener);
this.retrieverCache.clear();
}
}
@Override
public void removeApplicationListenerBean(String listenerBeanName) {
synchronized (this.retrievalMutex) {
this.defaultRetriever.applicationListenerBeans.remove(listenerBeanName);
this.retrieverCache.clear();
}
}
@Override
public void removeAllListeners() {
synchronized (this.retrievalMutex) {
this.defaultRetriever.applicationListeners.clear();
this.defaultRetriever.applicationListenerBeans.clear();
this.retrieverCache.clear();
}
}
/**
* Return a Collection containing all ApplicationListeners.
* @return a Collection of ApplicationListeners
* @see org.springframework.context.ApplicationListener
*/
protected Collection<ApplicationListener<?>> getApplicationListeners() {
synchronized (this.retrievalMutex) {
return this.defaultRetriever.getApplicationListeners();
}
}
/**
* Return a Collection of ApplicationListeners matching the given
* event type. Non-matching listeners get excluded early.
* @param event the event to be propagated. Allows for excluding
* non-matching listeners early, based on cached matching information.
* @param eventType the event type
* @return a Collection of ApplicationListeners
* @see org.springframework.context.ApplicationListener
*/
protected Collection<ApplicationListener<?>> getApplicationListeners(
ApplicationEvent event, ResolvableType eventType) {
Object source = event.getSource();
Class<?> sourceType = (source != null ? source.getClass() : null);
ListenerCacheKey cacheKey = new ListenerCacheKey(eventType, sourceType);
// Quick check for existing entry on ConcurrentHashMap...
ListenerRetriever retriever = this.retrieverCache.get(cacheKey);
if (retriever != null) {
return retriever.getApplicationListeners();
}
if (this.beanClassLoader == null ||
(ClassUtils.isCacheSafe(event.getClass(), this.beanClassLoader) &&
(sourceType == null || ClassUtils.isCacheSafe(sourceType, this.beanClassLoader)))) {
// Fully synchronized building and caching of a ListenerRetriever
synchronized (this.retrievalMutex) {
retriever = this.retrieverCache.get(cacheKey);
if (retriever != null) {
return retriever.getApplicationListeners();
}
retriever = new ListenerRetriever(true);
Collection<ApplicationListener<?>> listeners =
retrieveApplicationListeners(eventType, sourceType, retriever);
this.retrieverCache.put(cacheKey, retriever);
return listeners;
}
}
else {
// No ListenerRetriever caching -> no synchronization necessary
return retrieveApplicationListeners(eventType, sourceType, null);
}
}
/**
* Actually retrieve the application listeners for the given event and source type.
* @param eventType the event type
* @param sourceType the event source type
* @param retriever the ListenerRetriever, if supposed to populate one (for caching purposes)
* @return the pre-filtered list of application listeners for the given event and source type
*/
private Collection<ApplicationListener<?>> retrieveApplicationListeners(
ResolvableType eventType, @Nullable Class<?> sourceType, @Nullable ListenerRetriever retriever) {
List<ApplicationListener<?>> allListeners = new ArrayList<>();
Set<ApplicationListener<?>> listeners;
Set<String> listenerBeans;
synchronized (this.retrievalMutex) {
listeners = new LinkedHashSet<>(this.defaultRetriever.applicationListeners);
listenerBeans = new LinkedHashSet<>(this.defaultRetriever.applicationListenerBeans);
}
for (ApplicationListener<?> listener : listeners) {
if (supportsEvent(listener, eventType, sourceType)) {
if (retriever != null) {
retriever.applicationListeners.add(listener);
}
allListeners.add(listener);
}
}
if (!listenerBeans.isEmpty()) {
BeanFactory beanFactory = getBeanFactory();
for (String listenerBeanName : listenerBeans) {
try {
Class<?> listenerType = beanFactory.getType(listenerBeanName);
if (listenerType == null || supportsEvent(listenerType, eventType)) {
ApplicationListener<?> listener =
beanFactory.getBean(listenerBeanName, ApplicationListener.class);
if (!allListeners.contains(listener) && supportsEvent(listener, eventType, sourceType)) {
if (retriever != null) {
if (beanFactory.isSingleton(listenerBeanName)) {
retriever.applicationListeners.add(listener);
}
else {
retriever.applicationListenerBeans.add(listenerBeanName);
}
}
allListeners.add(listener);
}
}
}
catch (NoSuchBeanDefinitionException ex) {
// Singleton listener instance (without backing bean definition) disappeared -
// probably in the middle of the destruction phase
}
}
}
AnnotationAwareOrderComparator.sort(allListeners);
if (retriever != null && retriever.applicationListenerBeans.isEmpty()) {
retriever.applicationListeners.clear();
retriever.applicationListeners.addAll(allListeners);
}
return allListeners;
}
/**
* Filter a listener early through checking its generically declared event
* type before trying to instantiate it.
* <p>If this method returns {@code true} for a given listener as a first pass,
* the listener instance will get retrieved and fully evaluated through a
* {@link #supportsEvent(ApplicationListener, ResolvableType, Class)} call afterwards.
* @param listenerType the listener's type as determined by the BeanFactory
* @param eventType the event type to check
* @return whether the given listener should be included in the candidates
* for the given event type
*/
protected boolean supportsEvent(Class<?> listenerType, ResolvableType eventType) {
if (GenericApplicationListener.class.isAssignableFrom(listenerType) ||
SmartApplicationListener.class.isAssignableFrom(listenerType)) {
return true;
}
ResolvableType declaredEventType = GenericApplicationListenerAdapter.resolveDeclaredEventType(listenerType);
return (declaredEventType == null || declaredEventType.isAssignableFrom(eventType));
}
/**
* Determine whether the given listener supports the given event.
* <p>The default implementation detects the {@link SmartApplicationListener}
* and {@link GenericApplicationListener} interfaces. In case of a standard
* {@link ApplicationListener}, a {@link GenericApplicationListenerAdapter}
* will be used to introspect the generically declared type of the target listener.
* @param listener the target listener to check
* @param eventType the event type to check against
* @param sourceType the source type to check against
* @return whether the given listener should be included in the candidates
* for the given event type
*/
protected boolean supportsEvent(
ApplicationListener<?> listener, ResolvableType eventType, @Nullable Class<?> sourceType) {
GenericApplicationListener smartListener = (listener instanceof GenericApplicationListener ?
(GenericApplicationListener) listener : new GenericApplicationListenerAdapter(listener));
return (smartListener.supportsEventType(eventType) && smartListener.supportsSourceType(sourceType));
}
/**
* Cache key for ListenerRetrievers, based on event type and source type.
*/
private static final class ListenerCacheKey implements Comparable<ListenerCacheKey> {
private final ResolvableType eventType;
@Nullable
private final Class<?> sourceType;
public ListenerCacheKey(ResolvableType eventType, @Nullable Class<?> sourceType) {
Assert.notNull(eventType, "Event type must not be null");
this.eventType = eventType;
this.sourceType = sourceType;
}
@Override
public boolean equals(Object other) {
if (this == other) {
return true;
}
ListenerCacheKey otherKey = (ListenerCacheKey) other;
return (this.eventType.equals(otherKey.eventType) &&
ObjectUtils.nullSafeEquals(this.sourceType, otherKey.sourceType));
}
@Override
public int hashCode() {
return this.eventType.hashCode() * 29 + ObjectUtils.nullSafeHashCode(this.sourceType);
}
@Override
public String toString() {
return "ListenerCacheKey [eventType = " + this.eventType + ", sourceType = " + this.sourceType + "]";
}
@Override
public int compareTo(ListenerCacheKey other) {
int result = this.eventType.toString().compareTo(other.eventType.toString());
if (result == 0) {
if (this.sourceType == null) {
return (other.sourceType == null ? 0 : -1);
}
if (other.sourceType == null) {
return 1;
}
result = this.sourceType.getName().compareTo(other.sourceType.getName());
}
return result;
}
}
/**
* Helper class that encapsulates a specific set of target listeners,
* allowing for efficient retrieval of pre-filtered listeners.
* <p>An instance of this helper gets cached per event type and source type.
*/
private class ListenerRetriever {
public final Set<ApplicationListener<?>> applicationListeners = new LinkedHashSet<>();
public final Set<String> applicationListenerBeans = new LinkedHashSet<>();
private final boolean preFiltered;
public ListenerRetriever(boolean preFiltered) {
this.preFiltered = preFiltered;
}
public Collection<ApplicationListener<?>> getApplicationListeners() {
List<ApplicationListener<?>> allListeners = new ArrayList<>(
this.applicationListeners.size() + this.applicationListenerBeans.size());
allListeners.addAll(this.applicationListeners);
if (!this.applicationListenerBeans.isEmpty()) {
BeanFactory beanFactory = getBeanFactory();
for (String listenerBeanName : this.applicationListenerBeans) {
try {
ApplicationListener<?> listener = beanFactory.getBean(listenerBeanName, ApplicationListener.class);
if (this.preFiltered || !allListeners.contains(listener)) {
allListeners.add(listener);
}
}
catch (NoSuchBeanDefinitionException ex) {
// Singleton listener instance (without backing bean definition) disappeared -
// probably in the middle of the destruction phase
}
}
}
if (!this.preFiltered || !this.applicationListenerBeans.isEmpty()) {
AnnotationAwareOrderComparator.sort(allListeners);
}
return allListeners;
}
}
}
