public static final String BEFORE_START_EVENT = "before_start";
    public static final String AFTER_START_EVENT = "after_start";
    public static final String STOP_EVENT = "stop";
    public static final String BEFORE_STOP_EVENT = "before_stop";
    public static final String AFTER_STOP_EVENT = "after_stop";
    public static final String AFTER_DESTROY_EVENT = "after_destroy";
    public static final String BEFORE_DESTROY_EVENT = "before_destroy";
    /**
     * The LifecycleEvent type for the "periodic" event.
     * 周期性事件（后臺(tái)線程定時(shí)執(zhí)行一些事情，比如：熱部署、熱替換）
     */
    public static final String PERIODIC_EVENT = "periodic";
    public static final String CONFIGURE_START_EVENT = "configure_start";
    public static final String CONFIGURE_STOP_EVENT = "configure_stop";

    public void addLifecycleListener(LifecycleListener listener);
    public LifecycleListener[] findLifecycleListeners();
    public void removeLifecycleListener(LifecycleListener listener);

public interface LifecycleListener {
    /**
     * Acknowledge the occurrence of the specified event.
     *  觸發(fā)監(jiān)聽(tīng)器后要執(zhí)行邏輯的方法
     * @param event LifecycleEvent that has occurred
     */
    public void lifecycleEvent(LifecycleEvent event);
}

public final class LifecycleEvent extends EventObject {
    private static final long serialVersionUID = 1L;
    /**
     * Construct a new LifecycleEvent with the specified parameters.
     *
     * @param lifecycle Component on which this event occurred
     * @param type Event type (required)
     * @param data Event data (if any)
     */
    public LifecycleEvent(Lifecycle lifecycle, String type, Object data) {
        super(lifecycle); // 向上轉(zhuǎn)型，可接受一切實(shí)現(xiàn)了生命周期的組件
        this.type = type;
        this.data = data;
    }
    /**
     * The event data associated with this event.
     * 攜帶的額外的數(shù)據(jù)，傳遞給監(jiān)聽(tīng)器的數(shù)據(jù)
     */
    private final Object data;
    /**
     * The event type this instance represents.
     * 事件類型
     */
    private final String type;
    /**
     * @return the event data of this event.
     */
    public Object getData() {
        return data;
    }
    /**
     * @return the Lifecycle on which this event occurred.
     */
    public Lifecycle getLifecycle() {
        return (Lifecycle) getSource();
    }
    /**
     * @return the event type of this event.
     */
    public String getType() {
        return this.type;
    }
}

// 存儲(chǔ)了所有的實(shí)現(xiàn)了LifecycleListener接口的監(jiān)聽(tīng)器 
private final List<LifecycleListener> lifecycleListeners = new CopyOnWriteArrayList<>();

    /**
     * Allow sub classes to fire {@link Lifecycle} events.
     *     監(jiān)聽(tīng)器觸發(fā)相關(guān)的事件
     * @param type  Event type  事件類型
     * @param data  Data associated with event.
     */
    protected void fireLifecycleEvent(String type, Object data) {
        LifecycleEvent event = new LifecycleEvent(this, type, data);
        for (LifecycleListener listener : lifecycleListeners) {
            listener.lifecycleEvent(event);
        }
    }

 
    // 添加監(jiān)聽(tīng)器
    @Override
    public void addLifecycleListener(LifecycleListener listener) {
        lifecycleListeners.add(listener);
    }
    // 查找所有的監(jiān)聽(tīng)并轉(zhuǎn)換為了數(shù)組類型
    @Override
    public LifecycleListener[] findLifecycleListeners() {
        return lifecycleListeners.toArray(new LifecycleListener[0]);
    }
    // 移除某個(gè)監(jiān)聽(tīng)器
    @Override
    public void removeLifecycleListener(LifecycleListener listener) {
        lifecycleListeners.remove(listener);
    }

    /**
     * 實(shí)現(xiàn)了 Lifecycle 中定義的init方法
     * 該方法和對(duì)應(yīng)的組件的狀態(tài)產(chǎn)生的關(guān)聯(lián)
     * @throws LifecycleException
     */
    @Override
    public final synchronized void init() throws LifecycleException {
        if (!state.equals(LifecycleState.NEW)) {
            // 無(wú)效的操作  只有狀態(tài)為 New 的才能調(diào)用init方法進(jìn)入初始化
            invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
        }
        try {
            // 設(shè)置狀態(tài)為初始化進(jìn)行中....同步在方法中會(huì)觸發(fā)對(duì)應(yīng)的事件
            setStateInternal(LifecycleState.INITIALIZING, null, false);
            initInternal(); // 交給子類具體的實(shí)現(xiàn) 初始化操作
            // 更新?tīng)顟B(tài)為初始化完成 同步在方法中會(huì)觸發(fā)對(duì)應(yīng)的事件
            setStateInternal(LifecycleState.INITIALIZED, null, false);
        } catch (Throwable t) {
            handleSubClassException(t, "lifecycleBase.initFail", toString());
        }
    }

        // ....
        this.state = state; // 更新?tīng)顟B(tài)
        // 根據(jù)狀態(tài)和事件的綁定關(guān)系獲取對(duì)應(yīng)的事件
        String lifecycleEvent = state.getLifecycleEvent();
        if (lifecycleEvent != null) {
            // 發(fā)布對(duì)應(yīng)的事件
            fireLifecycleEvent(lifecycleEvent, data);
        }