Tomcat生命周期详解

    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（后台线程定时执行一些事情，比如：热部署、热替换）
     */
    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.
     *  触发监听器后要执行逻辑的方法
     * @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); // 向上转型，可接受一切实现了生命周期的组件
        this.type = type;
        this.data = data;
    }
    /**
     * The event data associated with this event.
     * 携带的额外的数据，传递给监听器的数据
     */
    private final Object data;
    /**
     * The event type this instance represents.
     * 事件类型
     */
    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;
    }
}

// 存储了所有的实现了LifecycleListener接口的监听器 
private final List<LifecycleListener> lifecycleListeners = new CopyOnWriteArrayList<>();

    /**
     * Allow sub classes to fire {@link Lifecycle} events.
     *     监听器触发相关的事件
     * @param type  Event type  事件类型
     * @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);
        }
    }

 
    // 添加监听器
    @Override
    public void addLifecycleListener(LifecycleListener listener) {
        lifecycleListeners.add(listener);
    }
    // 查找所有的监听并转换为了数组类型
    @Override
    public LifecycleListener[] findLifecycleListeners() {
        return lifecycleListeners.toArray(new LifecycleListener[0]);
    }
    // 移除某个监听器
    @Override
    public void removeLifecycleListener(LifecycleListener listener) {
        lifecycleListeners.remove(listener);
    }

    /**
     * 实现了 Lifecycle 中定义的init方法
     * 该方法和对应的组件的状态产生的关联
     * @throws LifecycleException
     */
    @Override
    public final synchronized void init() throws LifecycleException {
        if (!state.equals(LifecycleState.NEW)) {
            // 无效的操作  只有状态为 New 的才能调用init方法进入初始化
            invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
        }
        try {
            // 设置状态为初始化进行中....同步在方法中会触发对应的事件
            setStateInternal(LifecycleState.INITIALIZING, null, false);
            initInternal(); // 交给子类具体的实现 初始化操作
            // 更新状态为初始化完成 同步在方法中会触发对应的事件
            setStateInternal(LifecycleState.INITIALIZED, null, false);
        } catch (Throwable t) {
            handleSubClassException(t, "lifecycleBase.initFail", toString());
        }
    }

        // ....
        this.state = state; // 更新状态
        // 根据状态和事件的绑定关系获取对应的事件
        String lifecycleEvent = state.getLifecycleEvent();
        if (lifecycleEvent != null) {
            // 发布对应的事件
            fireLifecycleEvent(lifecycleEvent, data);
        }