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add springboot event listener source code analysis
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‎springboot-source-code-analysis/(7)事件监听器触发机制解析.md

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### 事件监听器触发机制解析
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#### 以SpringBoot Staring事件具例子
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- SpringContext#run方法中的，listeners.staring()方法
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```java
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/**
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* Run the Spring application, creating and refreshing a new
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* {@link ApplicationContext}.
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* @param args the application arguments (usually passed from a Java main method)
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* @return a running {@link ApplicationContext}
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*/
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public ConfigurableApplicationContext run(String... args) {
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StopWatch stopWatch = new StopWatch();
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stopWatch.start();
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ConfigurableApplicationContext context = null;
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Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
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configureHeadlessProperty();
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SpringApplicationRunListeners listeners = getRunListeners(args);
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// 告知框架已经开始启动
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listeners.starting();
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try {
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```
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- SpringApplicationRunListeners#starting() 内部方法
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```java
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public void starting() {
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// 调用 SpringApplicationRunListenser#staring() 方法
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for (SpringApplicationRunListener listener : this.listeners) {
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listener.starting();
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}
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}
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```
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- SpringApplicationRunListener方法，定义了框架各个阶段的事件监听方法
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```java
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/**
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* Listener for the {@link SpringApplication} {@code run} method.
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* {@link SpringApplicationRunListener}s are loaded via the {@link SpringFactoriesLoader}
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* and should declare a public constructor that accepts a {@link SpringApplication}
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* instance and a {@code String[]} of arguments. A new
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* {@link SpringApplicationRunListener} instance will be created for each run.
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*
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* @author Phillip Webb
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* @author Dave Syer
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* @author Andy Wilkinson
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* @since 1.0.0
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*/
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public interface SpringApplicationRunListener {
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/**
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* Called immediately when the run method has first started. Can be used for very
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* early initialization.
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*/
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void starting();
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/**
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* Called once the environment has been prepared, but before the
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* {@link ApplicationContext} has been created.
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* @param environment the environment
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*/
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void environmentPrepared(ConfigurableEnvironment environment);
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/**
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* Called once the {@link ApplicationContext} has been created and prepared, but
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* before sources have been loaded.
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* @param context the application context
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*/
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void contextPrepared(ConfigurableApplicationContext context);
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/**
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* Called once the application context has been loaded but before it has been
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* refreshed.
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* @param context the application context
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*/
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void contextLoaded(ConfigurableApplicationContext context);
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/**
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* The context has been refreshed and the application has started but
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* {@link CommandLineRunner CommandLineRunners} and {@link ApplicationRunner
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* ApplicationRunners} have not been called.
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* @param context the application context.
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* @since 2.0.0
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*/
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void started(ConfigurableApplicationContext context);
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/**
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* Called immediately before the run method finishes, when the application context has
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* been refreshed and all {@link CommandLineRunner CommandLineRunners} and
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* {@link ApplicationRunner ApplicationRunners} have been called.
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* @param context the application context.
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* @since 2.0.0
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*/
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void running(ConfigurableApplicationContext context);
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/**
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* Called when a failure occurs when running the application.
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* @param context the application context or {@code null} if a failure occurred before
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* the context was created
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* @param exception the failure
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* @since 2.0.0
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*/
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void failed(ConfigurableApplicationContext context, Throwable exception);
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}
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```
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- SpringApplicationRunListener#starting() 方法，通过 SimpleApplicationEventMulticaster 广播器发送 ApplicationStartingEvent 事件
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```java
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/**
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* {@link SpringApplicationRunListener} to publish {@link SpringApplicationEvent}s.
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* <p>
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* Uses an internal {@link ApplicationEventMulticaster} for the events that are fired
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* before the context is actually refreshed.
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*
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* @author Phillip Webb
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* @author Stephane Nicoll
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* @author Andy Wilkinson
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* @author Artsiom Yudovin
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* @since 1.0.0
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*/
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public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
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private final SpringApplication application;
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private final String[] args;
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private final SimpleApplicationEventMulticaster initialMulticaster;
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public EventPublishingRunListener(SpringApplication application, String[] args) {
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this.application = application;
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this.args = args;
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this.initialMulticaster = new SimpleApplicationEventMulticaster();
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for (ApplicationListener<?> listener : application.getListeners()) {
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this.initialMulticaster.addApplicationListener(listener);
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}
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}
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@Override
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public void starting() {
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// 通过广播器，发送ApplicationStaringEvent事件
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this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));
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}
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```
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- SimpleApplicationEventMulticaster#multicastEvent() 广播器发送方法
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```java
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public class SimpleApplicationEventMulticaster extends AbstractApplicationEventMulticaster {
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@Override
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public void multicastEvent(ApplicationEvent event) {
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multicastEvent(event, resolveDefaultEventType(event));
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}
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@Override
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public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
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ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
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Executor executor = getTaskExecutor();
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// 通过AbstractApplicationEventMulticaster#getApplicationListeners() 方法获得对该事件感兴趣的监听器列表
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for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
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if (executor != null) {
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executor.execute(() -> invokeListener(listener, event));
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}
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else {
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invokeListener(listener, event);
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}
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}
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}
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```
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- AbstractApplicationEventMulticaster#getApplicationListeners() 方法，获得对该事件感兴趣的监听器列表
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```java
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/**
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* Return a Collection of ApplicationListeners matching the given
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* event type. Non-matching listeners get excluded early.
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* @param event the event to be propagated. Allows for excluding
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* non-matching listeners early, based on cached matching information.
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* @param eventType the event type
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* @return a Collection of ApplicationListeners
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* @see org.springframework.context.ApplicationListener
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*/
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protected Collection<ApplicationListener<?>> getApplicationListeners(
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ApplicationEvent event, ResolvableType eventType) {
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Object source = event.getSource();
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Class<?> sourceType = (source != null ? source.getClass() : null);
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ListenerCacheKey cacheKey = new ListenerCacheKey(eventType, sourceType);
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// Quick check for existing entry on ConcurrentHashMap...
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ListenerRetriever retriever = this.retrieverCache.get(cacheKey);
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if (retriever != null) {
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return retriever.getApplicationListeners();
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}
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if (this.beanClassLoader == null ||
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(ClassUtils.isCacheSafe(event.getClass(), this.beanClassLoader) &&
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(sourceType == null || ClassUtils.isCacheSafe(sourceType, this.beanClassLoader)))) {
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// Fully synchronized building and caching of a ListenerRetriever
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// 避免其它线程操作ListenersCache缓存
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synchronized (this.retrievalMutex) {
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retriever = this.retrieverCache.get(cacheKey);
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// 双重检测锁
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if (retriever != null) {
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return retriever.getApplicationListeners();
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}
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retriever = new ListenerRetriever(true);
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// 通过AbstractApplicationEventMulicaster#retrieveApplicationListeners()获取感兴趣的事件监听列表
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Collection<ApplicationListener<?>> listeners =
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retrieveApplicationListeners(eventType, sourceType, retriever);
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this.retrieverCache.put(cacheKey, retriever);
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return listeners;
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}
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}
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else {
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// No ListenerRetriever caching -> no synchronization necessary
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return retrieveApplicationListeners(eventType, sourceType, null);
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}
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}
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```
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- 如果 this.retrieverCache 缓存获取不到 监听器列表，就从AbstractApplicationEventMulticaster#retrieveApplicationListeners()中获取
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```java
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/**
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* Actually retrieve the application listeners for the given event and source type.
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* @param eventType the event type
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* @param sourceType the event source type
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* @param retriever the ListenerRetriever, if supposed to populate one (for caching purposes)
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* @return the pre-filtered list of application listeners for the given event and source type
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*/
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private Collection<ApplicationListener<?>> retrieveApplicationListeners(
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ResolvableType eventType, @Nullable Class<?> sourceType, @Nullable ListenerRetriever retriever) {
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List<ApplicationListener<?>> allListeners = new ArrayList<>();
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Set<ApplicationListener<?>> listeners;
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Set<String> listenerBeans;
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// 通过互斥锁初始化Set<ApplicationListener>对象
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synchronized (this.retrievalMutex) {
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listeners = new LinkedHashSet<>(this.defaultRetriever.applicationListeners);
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listenerBeans = new LinkedHashSet<>(this.defaultRetriever.applicationListenerBeans);
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}
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/**
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获取所有事件监听器
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在 spring.factories 中定义的实践监听器
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# Application Listeners
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org.springframework.context.ApplicationListener=\
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org.springframework.boot.ClearCachesApplicationListener,\
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org.springframework.boot.builder.ParentContextCloserApplicationListener,\
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org.springframework.boot.context.FileEncodingApplicationListener,\
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org.springframework.boot.context.config.AnsiOutputApplicationListener,\
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org.springframework.boot.context.config.ConfigFileApplicationListener,\
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org.springframework.boot.context.config.DelegatingApplicationListener,\
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org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\
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org.springframework.boot.context.logging.LoggingApplicationListener,\
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org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener
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*/
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for (ApplicationListener<?> listener : listeners) {
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// 判断是否对该事件感兴趣
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if (supportsEvent(listener, eventType, sourceType)) {
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if (retriever != null) {
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retriever.applicationListeners.add(listener);
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}
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// 感兴趣就加入到集合当中
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allListeners.add(listener);
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}
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}
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if (!listenerBeans.isEmpty()) {
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BeanFactory beanFactory = getBeanFactory();
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for (String listenerBeanName : listenerBeans) {
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try {
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Class<?> listenerType = beanFactory.getType(listenerBeanName);
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if (listenerType == null || supportsEvent(listenerType, eventType)) {
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ApplicationListener<?> listener =
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beanFactory.getBean(listenerBeanName, ApplicationListener.class);
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if (!allListeners.contains(listener) && supportsEvent(listener, eventType, sourceType)) {
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if (retriever != null) {
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if (beanFactory.isSingleton(listenerBeanName)) {
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retriever.applicationListeners.add(listener);
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}
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else {
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retriever.applicationListenerBeans.add(listenerBeanName);
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}
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}
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allListeners.add(listener);
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}
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}
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}
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catch (NoSuchBeanDefinitionException ex) {
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// Singleton listener instance (without backing bean definition) disappeared -
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// probably in the middle of the destruction phase
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}
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}
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}
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// 监听器排序
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AnnotationAwareOrderComparator.sort(allListeners);
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if (retriever != null && retriever.applicationListenerBeans.isEmpty()) {
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retriever.applicationListeners.clear();
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retriever.applicationListeners.addAll(allListeners);
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}
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return allListeners;
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}
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```
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- 通过AbstractApplicationEventMuliticaster#supportEvent() 方法，判断该事件监听器，是否对该事件感兴趣？
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```java
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/**
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* Determine whether the given listener supports the given event.
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* <p>The default implementation detects the {@link SmartApplicationListener}
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* and {@link GenericApplicationListener} interfaces. In case of a standard
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* {@link ApplicationListener}, a {@link GenericApplicationListenerAdapter}
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* will be used to introspect the generically declared type of the target listener.
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* @param listener the target listener to check
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* @param eventType the event type to check against
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* @param sourceType the source type to check against
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* @return whether the given listener should be included in the candidates
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* for the given event type
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*/
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protected boolean supportsEvent(
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ApplicationListener<?> listener, ResolvableType eventType, @Nullable Class<?> sourceType) {
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// 判断当前事件监听器是否是GenericApplicationListerner接口类的实现类，如果不是的话，就做个委派，方便获取该事件监听器感兴趣事件
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GenericApplicationListener smartListener = (listener instanceof GenericApplicationListener ?
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(GenericApplicationListener) listener : new GenericApplicationListenerAdapter(listener));
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// 判断当前监听器是否感兴趣该事件
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return (smartListener.supportsEventType(eventType) && smartListener.supportsSourceType(sourceType));
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}
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```
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#### 获取监听器列表逻辑
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<img src="https://tva1.sinaimg.cn/large/008i3skNly1gunchq5avkj618e0u0q5l02.jpg" alt="image-20210920200242597" align="left" width="700" />
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- 通过AbstractApplicationEventMulticaster#getApplicationListeners()方法获取感兴趣事件监听器列表
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- 判断当前SpringBoot缓存中是否存在该事件感兴趣的监听器列表
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- 如果没有，调用通过AbstractApplicationEventMulicaster#retrieveApplicationListener()方法，获取所有事件监听器列表
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- 遍历所有事件监听器列表
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- 通过AbstractApplicationEventMuliticaster#supportsEvent() 方法查找出对该事件感兴趣的事件监听器
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- 将感兴趣的事件监听器列表加入SpirngBoot缓存中，并返回给事件触发器
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#### AbstractApplicationEventMuliticaster#supportEvent() 事件监听器匹配器触发条件
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<img src="/Users/huangyan110110114/Library/Application Support/typora-user-images/image-20210920201046825.png" alt="image-20210920201046825" align="left" width="850" />

‎springboot-source-code-analysis/pom.xml

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<parent>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-parent</artifactId>
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<version>2.4.0</version>
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<version>2.1.7.RELEASE</version>
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<relativePath/> <!-- lookup parent from repository -->
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</parent>
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<groupId>com.ipman.source.code.analysis.springboot</groupId>

‎springboot-source-code-analysis/src/test/java/com/example/springboot/source/code/analysis/SpringbootSourceCodeAnalysisApplicationTests.java

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import com.example.springboot.source.code.analysis.event.RainListener;
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import com.example.springboot.source.code.analysis.event.WeatherRunListener;
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import org.junit.jupiter.api.Test;
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import org.junit.Test;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.boot.test.context.SpringBootTest;
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