Springboot listener

 

在启动流程中，会出发许多ApplicationEvent。这时会调用对应的listener的onApplicationEvent方法。ApplicationEvent时观察者模式， 

(1) 实体继承ApplicationEvent

(2) 注入的Listener 实现接口ApplicationListener， 触发后的处理逻辑在onApplicationnEvent中

(3) 事件发起方经过ApplicationContext 实例的publishEvent方法将 (1)的实体传入(2)

 

SpringBoot 启动时的入口方法SpringApplication.run 内部实现为

public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) { return new SpringApplication(primarySources).run(args); }

第一步 new SpringApplication 内部会注入系统Listener  具体的listeners参见 https://blog.csdn.net/zl1zl2zl3/article/details/79765725

this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));

第二步 调用 run(args)  启动Listener

SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting();

第二步 2.1 如何获取监听器：在getRunListeners中会读取配置文件，加载的是Springboot META-INF/spring.factories 中的 org.springframework.boot.context.event.EventPublishingRunListener， 并生成"事件发布启动监听器"的工厂实例

private SpringApplicationRunListeners getRunListeners(String[] args) { Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class }; return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances( SpringApplicationRunListener.class, types, this, args)); } private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) { return getSpringFactoriesInstances(type, new Class<?>[] {}); } private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) { ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); // 使用Set确保的字符串的惟一性 Set<String> names = new LinkedHashSet<String>( SpringFactoriesLoader.loadFactoryNames(type, classLoader));// 1.载入工厂名称集合 List<T> instances = createSpringFactoriesInstances(type, parameterTypes,// 2.建立工厂实例  classLoader, args, names); AnnotationAwareOrderComparator.sort(instances);// 排序 return instances; }

META-INF/spring.factories

# Run Listeners 这里呢，看这里！！！！ org.springframework.boot.SpringApplicationRunListener=\ org.springframework.boot.context.event.EventPublishingRunListener

 

第二步 2.2 启动监听 starting()

SpringApplicationRunListeners listeners = this.getRunListeners(args); //若是有监听器监听启动事件，则执行对应的动做 listeners.starting();

 

当前监听是EventPublishingRunListener，starting 方法以下

public void starting() { this.initialMulticaster .multicastEvent(new ApplicationStartedEvent(this.application, this.args)); } public void multicastEvent(ApplicationEvent event) { multicastEvent(event, resolveDefaultEventType(event)); } public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) { ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event)); for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) { Executor executor = getTaskExecutor(); if (executor != null) { executor.execute(new Runnable() { @Override public void run() { invokeListener(listener, event); } }); } else { invokeListener(listener, event); } } }