Tomcat中Lifecycle

LifeCycle

节选部分源码、源码版本 Tomcat8.5

作用

​ 组件生命周期方法的通用接口。 Catalina组件可以实现此接口（以及它们支持的功能的适当接口），以便提供一致的机制来启动和停止组件

状态图

接口定义

public interface Lifecycle {
    // 13个状态常量值
    public static final String BEFORE_INIT_EVENT = "before_init";
    public static final String AFTER_INIT_EVENT = "after_init";
    public static final String START_EVENT = "start";
    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";
    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";
    // 3个监听器方法
    public void addLifecycleListener(LifecycleListener listener);
    public LifecycleListener[] findLifecycleListeners();
    public void removeLifecycleListener(LifecycleListener listener);
    // 4个生命周期方法
    public void init() throws LifecycleException;
    public void start() throws LifecycleException;
    public void stop() throws LifecycleException;
    public void destroy() throws LifecycleException;
    // 2个当前状态方法
    public LifecycleState getState();
    public String getStateName();
}

默认实现类

public abstract class LifecycleBase implements Lifecycle {
    // 源组件的当前状态,不同状态触发不同事件
    private volatile LifecycleState state = LifecycleState.NEW;
}

监听器相关方法

// 用于事件通知的已注册LifecycleListener列表
private final List<LifecycleListener> lifecycleListeners = 
    new CopyOnWriteArrayList<>();

@Override
public void addLifecycleListener(LifecycleListener listener) {
    lifecycleListeners.add(listener);
}

@Override
public LifecycleListener[] findLifecycleListeners() {
    return lifecycleListeners.toArray(new LifecycleListener[0]);
}

@Override
public void removeLifecycleListener(LifecycleListener listener) {
    lifecycleListeners.remove(listener);
}

// 子类根据当前状态触发不同事件，实现不同操作
protected void fireLifecycleEvent(String type, Object data) {
    LifecycleEvent event = new LifecycleEvent(this, type, data);
    for (LifecycleListener listener : lifecycleListeners) {
        listener.lifecycleEvent(event);
    }
}

生命周期方法

init方法

@Override
public final synchronized void init() throws LifecycleException {
    // 只有 NEW 状态可以调用
    if (!state.equals(LifecycleState.NEW)) {
        invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
    }
    // 设置 生命周期状态 -- INITIALIZING，触发相应事件
    setStateInternal(LifecycleState.INITIALIZING, null, false);
    // 模板方法，由具体子类实现
    initInternal();
    // 执行完成，设置生命周期状态 -- INITIALIZED，触发相应事件
    setStateInternal(LifecycleState.INITIALIZED, null, false);
}

Start方法

@Override
public final synchronized void start() throws LifecycleException {
    // 此三种状态不执行
    if (LifecycleState.STARTING_PREP.equals(state) ||      
        LifecycleState.STARTING.equals(state) ||
        LifecycleState.STARTED.equals(state)) {
        return;
    }
    // NEW 状态 执行 init 方法
    if (state.equals(LifecycleState.NEW)) {
        init();
    // 启动失败，调用 stop 方法
    } else if (state.equals(LifecycleState.FAILED)) {
        stop();
    // 其它状态，非法操作
    } else if (!state.equals(LifecycleState.INITIALIZED) &&
            !state.equals(LifecycleState.STOPPED)) {
        throw new LifecycleException()
    }
    // 设置启动状态为 STARTING_PREP【开始准备】
    setStateInternal(LifecycleState.STARTING_PREP, null, false);
    startInternal();
    // 调用完成后判断组件启动状态
    if (state.equals(LifecycleState.FAILED)) {
        stop();
    } else if (!state.equals(LifecycleState.STARTING)) {
        throw new LifecycleException();
    } else {
        setStateInternal(LifecycleState.STARTED, null, false);
    }
}

stop方法

@Override
public final synchronized void stop() throws LifecycleException {
    // STOPPING_PREP、STOPPING、STOPPED此三种状态不予执行
    if (LifecycleState.STOPPING_PREP.equals(state) || 
        LifecycleState.STOPPING.equals(state) ||
        LifecycleState.STOPPED.equals(state)) {
        return;
    }
    // 如果状态为 NEW、修改为 STOPPED
    if (state.equals(LifecycleState.NEW)) {
        state = LifecycleState.STOPPED;
        return;
    }
    // 不为 STARTED、FAILED 2种状态，抛出异常
    if (!state.equals(LifecycleState.STARTED) && 
        !state.equals(LifecycleState.FAILED)) {
        throw new LifecycleException();
    }
    try {
        // 启动失败，触发事件，否则设置生命周期状态
        if (state.equals(LifecycleState.FAILED)) {
            fireLifecycleEvent(BEFORE_STOP_EVENT, null);
        } else {
            setStateInternal(LifecycleState.STOPPING_PREP, null, false);
        }
        // 调用模板方法
        stopInternal();
        if (!state.equals(LifecycleState.STOPPING) && 
            !state.equals(LifecycleState.FAILED)) {
            throw new LifecycleException();
        }
        setStateInternal(LifecycleState.STOPPED, null, false);
    } catch (Throwable t) {
        setStateInternal(LifecycleState.FAILED, null, false);
        throw new LifecycleException();
    } finally {
        if (this instanceof Lifecycle.SingleUse) {
            setStateInternal(LifecycleState.STOPPED, null, false);
            destroy();
        }
    }
}

destroy方法

@Override
public final synchronized void destroy() throws LifecycleException {
    // 启动失败，先调用 stop 方法
    if (LifecycleState.FAILED.equals(state)) {
        stop();
    }
    // DESTROYING、DESTROYED不执行了
    if (LifecycleState.DESTROYING.equals(state) ||
        LifecycleState.DESTROYED.equals(state)) {
        return;
    }
    // 非法状态
    if (!state.equals(LifecycleState.STOPPED) &&
        !state.equals(LifecycleState.FAILED) &&
        !state.equals(LifecycleState.NEW) &&
        !state.equals(LifecycleState.INITIALIZED)) {
        throw new LifecycleException();
    }

    try {
        setStateInternal(LifecycleState.DESTROYING, null, false);
        destroyInternal();
        setStateInternal(LifecycleState.DESTROYED, null, false);
    } catch (Throwable t) {
        setStateInternal(LifecycleState.FAILED, null, false);
        throw new LifecycleException();
    }
}

设置状态方法

private synchronized void setStateInternal(LifecycleState state,
        Object data, boolean check) throws LifecycleException {

    // 检查参数
    if (check) {
        if (state == null) {
            throw new LifecycleException();
            return;
        }
        if (!(state == LifecycleState.FAILED ||
                (this.state == LifecycleState.STARTING_PREP &&
                        state == LifecycleState.STARTING) ||
                (this.state == LifecycleState.STOPPING_PREP &&
                        state == LifecycleState.STOPPING) ||
                (this.state == LifecycleState.FAILED &&
                        state == LifecycleState.STOPPING))) {
            throw new LifecycleException();
        }
    }
    this.state = state;
    String lifecycleEvent = state.getLifecycleEvent();
    if (lifecycleEvent != null) {
        fireLifecycleEvent(lifecycleEvent, data);
    }
}

模板方法

• 四个模板方法，由子类具体实现

protected abstract void initInternal() throws LifecycleException;
protected abstract void startInternal() throws LifecycleException;
protected abstract void stopInternal() throws LifecycleException;
protected abstract void destroyInternal() throws LifecycleException;

总结

​ 通过提供init、start、stop、destory方法，通过相应的模板方法【模板设计模式】，提供组件的统一生命周期的管理、事件调度。