Springboot listener

 

在啓動流程中，會出發許多ApplicationEvent。這時會調用對應的listener的onApplicationEvent方法。ApplicationEvent時觀察者模式， 

(1) 實體繼承ApplicationEvent

(2) 注入的Listener 實現接口ApplicationListener， 觸發後的處理邏輯在onApplicationnEvent中

(3) 事件發起方經過ApplicationContext 實例的publishEvent方法將 (1)的實體傳入(2)

 

SpringBoot 啓動時的入口方法SpringApplication.run 內部實現爲

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

第一步 new SpringApplication 內部會注入系統Listener  具體的listeners參見 http://www.javashuo.com/article/p-yytkatbe-ew.html

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

第二步 調用 run(args)  啓動Listener

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

第二步 2.1 如何獲取監聽器：在getRunListeners中會讀取配置文件，加載的是Springboot META-INF/spring.factories 中的 org.springframework.boot.context.event.EventPublishingRunListener， 並生成"事件發佈啓動監聽器"的工廠實例

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確保的字符串的惟一性 Set<String> names = new LinkedHashSet<String>( SpringFactoriesLoader.loadFactoryNames(type, classLoader));// 1.載入工廠名稱集合 List<T> instances = createSpringFactoriesInstances(type, parameterTypes,// 2.建立工廠實例  classLoader, args, names); AnnotationAwareOrderComparator.sort(instances);// 排序 return instances; }

META-INF/spring.factories

# Run Listeners  這裏呢，看這裏！！！！
org.springframework.boot.SpringApplicationRunListener=\ org.springframework.boot.context.event.EventPublishingRunListener

 

第二步 2.2 啓動監聽 starting()

SpringApplicationRunListeners listeners = this.getRunListeners(args);
//若是有監聽器監聽啓動事件，則執行對應的動做
listeners.starting();

 

當前監聽是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); } } }