[pull] master from ipipman:master

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

@@ -0,0 +1,372 @@
+### 事件监听器触发机制解析
+
+
+
+#### 以SpringBoot Staring事件具例子
+
+- SpringContext#run方法中的，listeners.staring()方法
+
+```java
+	/**
+	 * Run the Spring application, creating and refreshing a new
+	 * {@link ApplicationContext}.
+	 * @param args the application arguments (usually passed from a Java main method)
+	 * @return a running {@link ApplicationContext}
+	 */
+	public ConfigurableApplicationContext run(String... args) {
+		StopWatch stopWatch = new StopWatch();
+		stopWatch.start();
+		ConfigurableApplicationContext context = null;
+		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
+		configureHeadlessProperty();
+		SpringApplicationRunListeners listeners = getRunListeners(args);
+    // 告知框架已经开始启动
+		listeners.starting();
+		try {
+```
+
+
+
+- SpringApplicationRunListeners#starting() 内部方法
+
+```java
+	public void starting() {
+    // 调用 SpringApplicationRunListenser#staring() 方法
+		for (SpringApplicationRunListener listener : this.listeners) {
+			listener.starting();
+		}
+	}
+```
+
+
+
+- SpringApplicationRunListener方法，定义了框架各个阶段的事件监听方法
+
+```java
+/**
+ * Listener for the {@link SpringApplication} {@code run} method.
+ * {@link SpringApplicationRunListener}s are loaded via the {@link SpringFactoriesLoader}
+ * and should declare a public constructor that accepts a {@link SpringApplication}
+ * instance and a {@code String[]} of arguments. A new
+ * {@link SpringApplicationRunListener} instance will be created for each run.
+ *
+ * @author Phillip Webb
+ * @author Dave Syer
+ * @author Andy Wilkinson
+ * @since 1.0.0
+ */
+public interface SpringApplicationRunListener {
+
+	/**
+	 * Called immediately when the run method has first started. Can be used for very
+	 * early initialization.
+	 */
+	void starting();
+
+	/**
+	 * Called once the environment has been prepared, but before the
+	 * {@link ApplicationContext} has been created.
+	 * @param environment the environment
+	 */
+	void environmentPrepared(ConfigurableEnvironment environment);
+
+	/**
+	 * Called once the {@link ApplicationContext} has been created and prepared, but
+	 * before sources have been loaded.
+	 * @param context the application context
+	 */
+	void contextPrepared(ConfigurableApplicationContext context);
+
+	/**
+	 * Called once the application context has been loaded but before it has been
+	 * refreshed.
+	 * @param context the application context
+	 */
+	void contextLoaded(ConfigurableApplicationContext context);
+
+	/**
+	 * The context has been refreshed and the application has started but
+	 * {@link CommandLineRunner CommandLineRunners} and {@link ApplicationRunner
+	 * ApplicationRunners} have not been called.
+	 * @param context the application context.
+	 * @since 2.0.0
+	 */
+	void started(ConfigurableApplicationContext context);
+
+	/**
+	 * Called immediately before the run method finishes, when the application context has
+	 * been refreshed and all {@link CommandLineRunner CommandLineRunners} and
+	 * {@link ApplicationRunner ApplicationRunners} have been called.
+	 * @param context the application context.
+	 * @since 2.0.0
+	 */
+	void running(ConfigurableApplicationContext context);
+
+	/**
+	 * Called when a failure occurs when running the application.
+	 * @param context the application context or {@code null} if a failure occurred before
+	 * the context was created
+	 * @param exception the failure
+	 * @since 2.0.0
+	 */
+	void failed(ConfigurableApplicationContext context, Throwable exception);
+
+}
+```
+
+
+
+- SpringApplicationRunListener#starting() 方法，通过 SimpleApplicationEventMulticaster 广播器发送 ApplicationStartingEvent 事件
+
+```java
+/**
+ * {@link SpringApplicationRunListener} to publish {@link SpringApplicationEvent}s.
+ * <p>
+ * Uses an internal {@link ApplicationEventMulticaster} for the events that are fired
+ * before the context is actually refreshed.
+ *
+ * @author Phillip Webb
+ * @author Stephane Nicoll
+ * @author Andy Wilkinson
+ * @author Artsiom Yudovin
+ * @since 1.0.0
+ */
+public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
+
+	private final SpringApplication application;
+
+	private final String[] args;
+
+	private final SimpleApplicationEventMulticaster initialMulticaster;
+
+	public EventPublishingRunListener(SpringApplication application, String[] args) {
+		this.application = application;
+		this.args = args;
+		this.initialMulticaster = new SimpleApplicationEventMulticaster();
+		for (ApplicationListener<?> listener : application.getListeners()) {
+			this.initialMulticaster.addApplicationListener(listener);
+		}
+	}
+
+	@Override
+	public void starting() {
+    // 通过广播器，发送ApplicationStaringEvent事件
+		this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));
+	}
+
+```
+
+
+
+- SimpleApplicationEventMulticaster#multicastEvent() 广播器发送方法
+
+```java
+public class SimpleApplicationEventMulticaster extends AbstractApplicationEventMulticaster {
+
+  @Override
+	public void multicastEvent(ApplicationEvent event) {
+		multicastEvent(event, resolveDefaultEventType(event));
+	}
+
+	@Override
+	public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
+		ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
+		Executor executor = getTaskExecutor();
+    // 通过AbstractApplicationEventMulticaster#getApplicationListeners() 方法获得对该事件感兴趣的监听器列表
+		for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
+			if (executor != null) {
+				executor.execute(() -> invokeListener(listener, event));
+			}
+			else {
+				invokeListener(listener, event);
+			}
+		}
+	}  
+```
+
+
+
+- AbstractApplicationEventMulticaster#getApplicationListeners() 方法，获得对该事件感兴趣的监听器列表
+
+```java
+	/**
+	 * 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
+      // 避免其它线程操作ListenersCache缓存
+			synchronized (this.retrievalMutex) {
+				retriever = this.retrieverCache.get(cacheKey);
+        // 双重检测锁
+				if (retriever != null) {
+					return retriever.getApplicationListeners();
+				}
+				retriever = new ListenerRetriever(true);
+        // 通过AbstractApplicationEventMulicaster#retrieveApplicationListeners()获取感兴趣的事件监听列表
+				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);
+		}
+	}
+```
+
+
+
+- 如果 this.retrieverCache 缓存获取不到 监听器列表，就从AbstractApplicationEventMulticaster#retrieveApplicationListeners()中获取
+
+```java
+/**
+	 * 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;
+    // 通过互斥锁初始化Set<ApplicationListener>对象
+		synchronized (this.retrievalMutex) {
+			listeners = new LinkedHashSet<>(this.defaultRetriever.applicationListeners);
+			listenerBeans = new LinkedHashSet<>(this.defaultRetriever.applicationListenerBeans);
+		}
+    /**
+    	获取所有事件监听器
+      在 spring.factories 中定义的实践监听器
+      # Application Listeners
+      org.springframework.context.ApplicationListener=\
+      org.springframework.boot.ClearCachesApplicationListener,\
+      org.springframework.boot.builder.ParentContextCloserApplicationListener,\
+      org.springframework.boot.context.FileEncodingApplicationListener,\
+      org.springframework.boot.context.config.AnsiOutputApplicationListener,\
+      org.springframework.boot.context.config.ConfigFileApplicationListener,\
+      org.springframework.boot.context.config.DelegatingApplicationListener,\
+      org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\
+      org.springframework.boot.context.logging.LoggingApplicationListener,\
+      org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener
+    */
+		for (ApplicationListener<?> listener : listeners) {
+      // 判断是否对该事件感兴趣
+			if (supportsEvent(listener, eventType, sourceType)) {
+				if (retriever != null) {
+					retriever.applicationListeners.add(listener);
+				}
+        // 感兴趣就加入到集合当中
+				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
+				}
+			}
+		}
+    // 监听器排序
+		AnnotationAwareOrderComparator.sort(allListeners);
+		if (retriever != null && retriever.applicationListenerBeans.isEmpty()) {
+			retriever.applicationListeners.clear();
+			retriever.applicationListeners.addAll(allListeners);
+		}
+		return allListeners;
+	}
+```
+
+
+
+- 通过AbstractApplicationEventMuliticaster#supportEvent() 方法，判断该事件监听器，是否对该事件感兴趣？
+
+```java
+	/**
+	 * 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) {
+
+    // 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
+		GenericApplicationListener smartListener = (listener instanceof GenericApplicationListener ?
+				(GenericApplicationListener) listener : new GenericApplicationListenerAdapter(listener));
+    // 判断当前监听器是否感兴趣该事件
+		return (smartListener.supportsEventType(eventType) && smartListener.supportsSourceType(sourceType));
+	}
+```
+
+
+
+
+
+#### 获取监听器列表逻辑
+
+<img src="https://tva1.sinaimg.cn/large/008i3skNly1gunchq5avkj618e0u0q5l02.jpg" alt="image-20210920200242597" align="left" width="700" />
+
+- 通过AbstractApplicationEventMulticaster#getApplicationListeners()方法获取感兴趣事件监听器列表
+- 判断当前SpringBoot缓存中是否存在该事件感兴趣的监听器列表
+- 如果没有，调用通过AbstractApplicationEventMulicaster#retrieveApplicationListener()方法，获取所有事件监听器列表
+- 遍历所有事件监听器列表
+- 通过AbstractApplicationEventMuliticaster#supportsEvent() 方法查找出对该事件感兴趣的事件监听器
+- 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
+
+
+
+#### AbstractApplicationEventMuliticaster#supportEvent() 事件监听器匹配器触发条件
+
+<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

@@ -5,7 +5,7 @@
     <parent>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-parent</artifactId>
-        <version>2.4.0</version>
+        <version>2.1.7.RELEASE</version>
         <relativePath/> <!-- lookup parent from repository -->
     </parent>
     <groupId>com.ipman.source.code.analysis.springboot</groupId>

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

@@ -2,7 +2,7 @@
 
 import com.example.springboot.source.code.analysis.event.RainListener;
 import com.example.springboot.source.code.analysis.event.WeatherRunListener;
-import org.junit.jupiter.api.Test;
+import org.junit.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;