ApplicationEventMulticaster是spring中事件广播器接口，负责事件的广播发布。AbstractApplicationContext中使用initApplicationEventMulticaster()初始化事件广播器。
public interface ApplicationEventMulticaster {
/**
* Add a listener to be notified of all events.
* @param listener the listener to add
*/
//添加事件监听器
void addApplicationListener(ApplicationListener<?> listener);
/**
* Add a listener bean to be notified of all events.
* @param listenerBeanName the name of the listener bean to add
*/
//添加事件监听器，使用容器中的bean
void addApplicationListenerBean(String listenerBeanName);
/**
* Remove a listener from the notification list.
* @param listener the listener to remove
*/
//移除事件监听器
void removeApplicationListener(ApplicationListener<?> listener);
/**
* Remove a listener bean from the notification list.
* @param listenerBeanName the name of the listener bean to remove
*/
void removeApplicationListenerBean(String listenerBeanName);
/**
* Remove all listeners registered with this multicaster.
* <p>After a remove call, the multicaster will perform no action
* on event notification until new listeners are registered.
*/
//移除所有事件监听器
void removeAllListeners();
/**
* Multicast the given application event to appropriate listeners.
* <p>Consider using {@link #multicastEvent(ApplicationEvent, ResolvableType)}
* if possible as it provides better support for generics-based events.
* @param event the event to multicast
*/
//发布事件
void multicastEvent(ApplicationEvent event);
/**
* Multicast the given application event to appropriate listeners.
* <p>If the {@code eventType} is {@code null}, a default type is built
* based on the {@code event} instance.
* @param event the event to multicast
* @param eventType the type of event (can be {@code null})
* @since 4.2
*/
//发布事件
void multicastEvent(ApplicationEvent event, @Nullable ResolvableType eventType);
}
AbstractApplicationContext中使用initApplicationEventMulticaster()初始化事件广播器。
applicationEventMulticaster的bean，这将该bean设为上下文中的事件广播器。applicationEventMulticaster的bean，默认创建SimpleApplicationEventMulticaster来代替。 /**
* Initialize the ApplicationEventMulticaster.
* Uses SimpleApplicationEventMulticaster if none defined in the context.
* @see org.springframework.context.event.SimpleApplicationEventMulticaster
*/
protected void initApplicationEventMulticaster() {
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
//如果beanFactory里面有applicationEventMulticaster，这使用容器里面的这个事件广播器
if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
this.applicationEventMulticaster =
beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
if (logger.isTraceEnabled()) {
logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
}
}
else {
//否则创建SimpleApplicationEventMulticaster来代替
this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
if (logger.isTraceEnabled()) {
logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
"[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
}
}
}
自定义广播器
/**
* @author liangwy
* @since 2022-5-16
*/
@Component
public class MyApplicationEventMulticaster implements ApplicationEventMulticaster {
private ConfigurableBeanFactory beanFactory;
private List<ApplicationListener<?>> listenerList;
public MyApplicationEventMulticaster(ConfigurableBeanFactory beanFactory){
this.beanFactory = beanFactory;
}
@Override
public void addApplicationListener(ApplicationListener<?> listener) {
listenerList.add(listener);
}
@Override
public void addApplicationListenerBean(String listenerBeanName) {
ApplicationListener bean = beanFactory.getBean(listenerBeanName, ApplicationListener.class);
addApplicationListener(bean);
}
@Override
public void removeApplicationListener(ApplicationListener<?> listener) {
listenerList.remove(listener);
}
@Override
public void removeApplicationListenerBean(String listenerBeanName) {
ApplicationListener bean = beanFactory.getBean(listenerBeanName, ApplicationListener.class);
removeApplicationListener(bean);
}
@Override
public void removeAllListeners() {
listenerList.clear();
}
@Override
public void multicastEvent(ApplicationEvent event) {
multicastEvent(event,ResolvableType.forInstance(event));
}
@Override
public void multicastEvent(ApplicationEvent event, @Nullable ResolvableType eventType) {
//判空
ResolvableType type = (eventType != null ? eventType : ResolvableType.forInstance(event));
//如果来自自定义事件,才进行事件分发（不建议这样，这里只是演示示例）
if (type.isAssignableFrom(MyApplicationEvent.class)){
//对监听器遍历处理事件
for (final ApplicationListener listener:listenerList){
listener.onApplicationEvent(event);
}
}
}
}
自定义监听器
/**
* @author liangwy
* @since 2022-5-16
*/
@Component
public class MyApplicationListener implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationEvent event) {
//事件处理
if (event instanceof MyApplicationEvent){
((MyApplicationEvent) event).toDo();
}
}
}
自定义事件
/**
* @author liangwy
* @since 2022-5-16
*/
public class MyApplicationEvent extends ApplicationEvent {
public String msg;
/**
* Create a new {@code ApplicationEvent}.
*
* @param source the object on which the event initially occurred or with
* which the event is associated (never {@code null})
*/
public MyApplicationEvent(Object source) {
super(source);
}
public MyApplicationEvent(Object source,String msg){
super(source);
this.msg = msg;
}
public void toDo(){
System.out.println(msg);
}
}
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(ApplicationMain.class);
applicationContext.getBeanFactory().registerCustomEditor(Date.class,TestPropertyEditorSupport.class);
applicationContext.publishEvent(new MyApplicationEvent("事件源","测试事件"));
测试结果
在控制台打印如下结果
测试事件
SimpleApplicationEventMulticaster是spring中一个ApplicationEventMulticaster实现类。看SimpleApplicationEventMulticaster，看multicastEvent方法部分即可。
@Override
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
//参试使用线程池执行
Executor executor = getTaskExecutor();
for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
if (executor != null) {
//线程执行
executor.execute(() -> invokeListener(listener, event));
}
else {
//直接调用
invokeListener(listener, event);
}
}
}