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