tomcat源码05 - 组件生命周期管理LifeCycle

是小崔啊2025-07-12 18:53

组件生命周期管理LifeCycle

文章目录

我们已经知道Catalina初始化了Server（它调用了 Server 类的 init 和 start 方法来启动 Tomcat）

会发现Server是Tomcat的配置文件server.xml的顶层元素

那这个阶段其实已经进入到Tomcat内部组件的详解；这时候有一个问题，这么多组件是如何管理它的生命周期的呢

一：生命周期管理引入

Server后续组件生命周期及其初始化

二：LifeCycle接口

理解Lifecycle主要有两点：第一是三类接口方法；第二是状态机。

1：一个标准的LifeCycle有哪些方法

分成三类去看：

java 复制代码 
public interface Lifecycle {
    /** ==============> 第1类：针对监听器 <================== **/
    // 添加监听器
    public void addLifecycleListener(LifecycleListener listener);
    // 获取所以监听器
    public LifecycleListener[] findLifecycleListeners();
    // 移除某个监听器
    public void removeLifecycleListener(LifecycleListener listener);

    /**  ==============> 第2类：针对控制流程 <================== **/
    // 初始化方法
    public void init() throws LifecycleException;
    // 启动方法
    public void start() throws LifecycleException;
    // 停止方法，和start对应
    public void stop() throws LifecycleException;
    // 销毁方法，和init对应
    public void destroy() throws LifecycleException;

    /**  ==============> 第3类：针对状态 <================== **/
    // 获取生命周期状态
    public LifecycleState getState();
    // 获取字符串类型的生命周期状态
    public String getStateName();
}

2：LifeCycle状态机有哪些状态

Tomcat 给各个组件定义了一些生命周期中的状态，在枚举类LifecycleState里：

java 复制代码 
public enum LifecycleState {
    NEW(false, null),
    INITIALIZING(false, Lifecycle.BEFORE_INIT_EVENT),
    INITIALIZED(false, Lifecycle.AFTER_INIT_EVENT),
    STARTING_PREP(false, Lifecycle.BEFORE_START_EVENT),
    STARTING(true, Lifecycle.START_EVENT),
    STARTED(true, Lifecycle.AFTER_START_EVENT),
    STOPPING_PREP(true, Lifecycle.BEFORE_STOP_EVENT),
    STOPPING(false, Lifecycle.STOP_EVENT),
    STOPPED(false, Lifecycle.AFTER_STOP_EVENT),
    DESTROYING(false, Lifecycle.BEFORE_DESTROY_EVENT),
    DESTROYED(false, Lifecycle.AFTER_DESTROY_EVENT),
    FAILED(false, null);

    private final boolean available;
    private final String lifecycleEvent;

    private LifecycleState(boolean available, String lifecycleEvent) {
        this.available = available;
        this.lifecycleEvent = lifecycleEvent;
    }
    ......
}

三：LifecycleBase

LifecycleBase是Lifecycle的基本实现

1：监听器相关

生命周期监听器保存在一个线程安全的CopyOnWriteArrayList中。

所以add和remove都是直接调用此List的相应方法。

findLifecycleListeners返回的是一个数组，为了线程安全，所以这儿会生成一个新数组。

java 复制代码 
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);
}

2：生命周期相关

2.1：init()
java 复制代码 
@Override
public final synchronized void init() throws LifecycleException {
    // 非NEW状态，不允许调用init()方法
    if (!state.equals(LifecycleState.NEW)) {
        invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
    }

    try {
        // 初始化逻辑之前，先将状态变更为`INITIALIZING`
        setStateInternal(LifecycleState.INITIALIZING, null, false);
        // 初始化，该方法为一个abstract方法，需要组件自行实现
        initInternal();
        // 初始化完成之后，状态变更为`INITIALIZED`
        setStateInternal(LifecycleState.INITIALIZED, null, false);
    } catch (Throwable t) {
        // 初始化的过程中，可能会有异常抛出，这时需要捕获异常，并将状态变更为`FAILED`
        ExceptionUtils.handleThrowable(t);
        setStateInternal(LifecycleState.FAILED, null, false);
        throw new LifecycleException(sm.getString("lifecycleBase.initFail",toString()), t);
    }
}


// 直接异常
private void invalidTransition(String type) throws LifecycleException {
    String msg = sm.getString("lifecycleBase.invalidTransition", type, toString(), state);
    throw new LifecycleException(msg);
}

setStateInternal方法用于维护状态，同时在状态转换成功之后触发事件。

为了状态的可见性，所以state声明为volatile类型的

java 复制代码 
private volatile LifecycleState state = LifecycleState.NEW;。

    private synchronized void setStateInternal(LifecycleState state, Object data, boolean check) throws LifecycleException {
    
    if (log.isDebugEnabled()) {
        log.debug(sm.getString("lifecycleBase.setState", this, state));
    }

    // 是否校验状态
    if (check) {
        // state不允许为null
        if (state == null) {
            invalidTransition("null");
            return;
        }
        // 判断状态，确定是否是无效的转换 -> invalidTransition(state.name());
        boolean flag1 = state == LifecycleState.FAILED;
        boolean flag2 = (this.state == LifecycleState.STARTING_PREP && state == LifecycleState.STARTING);
        boolean flag3 = (this.state == LifecycleState.STOPPING_PREP && state == LifecycleState.STOPPING);
        boolean flag4 = (this.state == LifecycleState.FAILED && state == LifecycleState.STOPPING);
        if (!(flag1 || flag2 || flag3 || flag4)) {
            invalidTransition(state.name());
        }
    }

    // 设置状态
    this.state = state;
    // 触发事件
    String lifecycleEvent = state.getLifecycleEvent();
    if (lifecycleEvent != null) {
        fireLifecycleEvent(lifecycleEvent, data);
    }
}

设置完 state 的状态之后，就触发该状态的事件了，通知事件监听器

java 复制代码 
private final List<LifecycleListener> lifecycleListeners = new CopyOnWriteArrayList<>();


protected void fireLifecycleEvent(String type, Object data) {
    // 声明生命周期事件
    LifecycleEvent event = new LifecycleEvent(this, type, data);
    for (LifecycleListener listener : lifecycleListeners) {
        listener.lifecycleEvent(event);
    }
}

这里的 LifecycleListener 对象是在解析 server.xml 文件时就已经创建好并加到 lifecycleListeners 里的

2.2：start()
java 复制代码 
@Override
public final synchronized void start() throws LifecycleException {
    // `STARTING_PREP`、`STARTING`和`STARTED时，将忽略start()逻辑
    boolean flag1 = LifecycleState.STARTING_PREP.equals(state);
    boolean flag2 = LifecycleState.STARTING.equals(state);
    boolean flag3 = LifecycleState.STARTED.equals(state)
    if (flag1 || flag2 || flag3) {
        if (log.isDebugEnabled()) {
            Exception e = new LifecycleException();
            log.debug(sm.getString("lifecycleBase.alreadyStarted", toString()), e);
        } else if (log.isInfoEnabled()) {
            log.info(sm.getString("lifecycleBase.alreadyStarted", toString()));
        }
        return;
    }

    // `NEW`状态时，执行init()方法
    if (state.equals(LifecycleState.NEW)) {
        init();
    }

    // `FAILED`状态时，执行stop()方法
    else if (state.equals(LifecycleState.FAILED)) {
        stop();
    }

    // 不是`INITIALIZED`和`STOPPED`时，则说明是非法的操作
    else if (!state.equals(LifecycleState.INITIALIZED) &&!state.equals(LifecycleState.STOPPED)) {
        invalidTransition(Lifecycle.BEFORE_START_EVENT);
    }

    try {
        // start前的状态设置
        setStateInternal(LifecycleState.STARTING_PREP, null, false);
        // start逻辑，抽象方法，由组件自行实现
        startInternal();
        // start过程中，可能因为某些原因失败，这时需要stop操作
        if (state.equals(LifecycleState.FAILED)) {
            stop();
        } else if (!state.equals(LifecycleState.STARTING)) {
            invalidTransition(Lifecycle.AFTER_START_EVENT);
        } else {
            // 设置状态为STARTED
            setStateInternal(LifecycleState.STARTED, null, false);
        }
    } catch (Throwable t) {
        ExceptionUtils.handleThrowable(t);
        setStateInternal(LifecycleState.FAILED, null, false);
        throw new LifecycleException(sm.getString("lifecycleBase.startFail", toString()), t);
    }
}
2.3：stop()
java 复制代码 
@Override
public final synchronized void stop() throws LifecycleException {
    // `STOPPING_PREP`、`STOPPING`和STOPPED时，将忽略stop()的执行
    if (LifecycleState.STOPPING_PREP.equals(state) || LifecycleState.STOPPING.equals(state) ||LifecycleState.STOPPED.equals(state)) {
        if (log.isDebugEnabled()) {
            Exception e = new LifecycleException();
            log.debug(sm.getString("lifecycleBase.alreadyStopped", toString()), e);
        } else if (log.isInfoEnabled()) {
            log.info(sm.getString("lifecycleBase.alreadyStopped", toString()));
        }
        return;
    }

    // `NEW`状态时，直接将状态变更为`STOPPED`
    if (state.equals(LifecycleState.NEW)) {
        state = LifecycleState.STOPPED;
        return;
    }

    // stop()的执行，必须要是`STARTED`和`FAILED`
    if (!state.equals(LifecycleState.STARTED) && !state.equals(LifecycleState.FAILED)) {
        invalidTransition(Lifecycle.BEFORE_STOP_EVENT);
    }

    try {
        // `FAILED`时，直接触发BEFORE_STOP_EVENT事件
        if (state.equals(LifecycleState.FAILED)) {
            fireLifecycleEvent(BEFORE_STOP_EVENT, null);
        } else {
            // 设置状态为STOPPING_PREP
            setStateInternal(LifecycleState.STOPPING_PREP, null, false);
        }

        // stop逻辑，抽象方法，组件自行实现
        stopInternal();

        // 保证组件实现的stopInternal返回的是stopping || failed，否则直接是无效状态
        if (!state.equals(LifecycleState.STOPPING) && !state.equals(LifecycleState.FAILED)) {
            invalidTransition(Lifecycle.AFTER_STOP_EVENT);
        }
        // 设置状态为STOPPED
        setStateInternal(LifecycleState.STOPPED, null, false);
    } catch (Throwable t) {
        ExceptionUtils.handleThrowable(t);
        // 如果中途有异常，failed状态
        setStateInternal(LifecycleState.FAILED, null, false);
        throw new LifecycleException(sm.getString("lifecycleBase.stopFail",toString()), t);
    } finally {
        if (this instanceof Lifecycle.SingleUse) {
            // Complete stop process first
            setStateInternal(LifecycleState.STOPPED, null, false);
            destroy();
        }
    }
}
2.4：destory()
java 复制代码 
@Override
public final synchronized void destroy() throws LifecycleException {
    // `FAILED`状态时，直接触发stop()逻辑
    if (LifecycleState.FAILED.equals(state)) {
        try {
            // Triggers clean-up
            stop();
        } catch (LifecycleException e) {
            // Just log. Still want to destroy.
            log.warn(sm.getString(
                "lifecycleBase.destroyStopFail", toString()), e);
        }
    }

    // `DESTROYING`和`DESTROYED`时，忽略destroy的执行
    if (LifecycleState.DESTROYING.equals(state) ||
        LifecycleState.DESTROYED.equals(state)) {

        if (log.isDebugEnabled()) {
            Exception e = new LifecycleException();
            log.debug(sm.getString("lifecycleBase.alreadyDestroyed", toString()), e);
        } else if (log.isInfoEnabled() && !(this instanceof Lifecycle.SingleUse)) {
            log.info(sm.getString("lifecycleBase.alreadyDestroyed", toString()));
        }

        return;
    }

    // 非法状态判断 - stopped || failed || new || initialized -> 非法状态
    if (!state.equals(LifecycleState.STOPPED) &&
        !state.equals(LifecycleState.FAILED) &&
        !state.equals(LifecycleState.NEW) &&
        !state.equals(LifecycleState.INITIALIZED)) {
        invalidTransition(Lifecycle.BEFORE_DESTROY_EVENT);
    }

    try {
        // destroy前状态设置
        setStateInternal(LifecycleState.DESTROYING, null, false);
        // 抽象方法，组件自行实现
        destroyInternal();
        // destroy后状态设置
        setStateInternal(LifecycleState.DESTROYED, null, false);
    } catch (Throwable t) {
        ExceptionUtils.handleThrowable(t);
        setStateInternal(LifecycleState.FAILED, null, false);
        throw new LifecycleException(
            sm.getString("lifecycleBase.destroyFail",toString()), t);
    }
}

3：总结

可以通过上面的源码看出，生命周期管理主要使用了状态机 + 模板模式实现的：

java 复制代码 
// 模板方法如下
// 初始化方法
protected abstract void initInternal() throws LifecycleException;
// 启动方法
protected abstract void startInternal() throws LifecycleException;
// 停止方法
protected abstract void stopInternal() throws LifecycleException;
// 销毁方法
protected abstract void destroyInternal() throws LifecycleException;
热门推荐
01Java类变量（静态变量）02集群聊天服务器---MySQL数据库的建立03KGG转MP3工具|非KGM文件|解密音频04使用Ruby接入实时行情API教程05【无标题】06Coze扣子平台完整体验和实践（附国内和国际版对比）07绿色建筑新态势：楼宇自控助力能效提升，推动成本优化新路径08基于odoo17的设计模式详解---单例模式09扣子（coze）实战|我用扣子搭建了一个自动分析小红薯笔记内容的AI应用|详细步骤拆解10基于uni-app的书法学习管理小程序的设计与实现