Spring之事件發布系統

Spring boot應用，啟動Spring容器大致有如下幾個過程：

• 容器開始啟動
• 初始化環境變量
• 初始化上下文
• 加載上下文
• 完成

對應的Spring應用的啟動器的監聽器可以監聽以上的過程，接口如下：

public interface SpringApplicationRunListener {

/**
* Called immediately when the run method has first started. Can be used for very
* early initialization.
*/
void started();

/**
* 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);

/**
* Called immediately before the run method finishes.
* @param context the application context or null if a failure occurred before the
* context was created
* @param exception any run exception or null if run completed successfully.
*/
void finished(ConfigurableApplicationContext context, Throwable exception);

}

監聽器

對應幾個關鍵事件

監聽器接口中的每個方法代表容器啟動過程一個階段，每一個階段可以自定義執行一系列任務。可以將SpringApplicationRunListener理解成一個命令模式（傳入一個對象，至於當前這個時間點，如何調用，不關心）。每一個階段執行的序列圖如下所示，其中任意方法，為SpringApplicationRunListener接口中定義的，此階段調用的方法。

SpringApplicationRunListeners是對多個SpringApplicationRunListener做了一次代理，聚合多個SpringApplicationRunListener,在任一個過程完成，會依次調用對應方法。

private final List<SpringApplicationRunListener> listeners;

SpringApplicationRunListeners(Log log,
Collection<? extends SpringApplicationRunListener> listeners) {
this.log = log;
this.listeners = new ArrayList<SpringApplicationRunListener>(listeners);
}

public void started() {
for (SpringApplicationRunListener listener : this.listeners) {
listener.started();
}
}

public void environmentPrepared(ConfigurableEnvironment environment) {
for (SpringApplicationRunListener listener : this.listeners) {
listener.environmentPrepared(environment);
}
}

SpringApplicationRunListener有一個特殊的實現EventPublishingRunListener，他的主要功能就是，在特定時間點出發特殊事件。

@Override
public void started() {
this.initialMulticaster.multicastEvent(new ApplicationStartedEvent(
this.application, this.args));
}

@Override
public void environmentPrepared(ConfigurableEnvironment environment) {
this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(
this.application, this.args, environment));
}

事件發布采用觀察者模式，整個事件發布流程如下圖。

Spring Boot+Nginx+Tomcat+SSL配置筆記 http://www.linuxidc.com/Linux/2016-01/127134.htm

Spring Boot 的詳細介紹：請點這裡
Spring Boot 的下載地址：請點這裡