概要

  • 什么是Lifecycle
  • Lifecycle中的方法
  • LifecycleBase
  • tomcat启动图

    什么是Lifecycle

Lifecycle，其实就是一个状态机，对组件的由生到死状态的管理。如下图所示：

  1.  *            start()
  2.  *  -----------------------------
  3.  *  |                           |
  4.  *  | init()                    |
  5.  * NEW -»-- INITIALIZING        |
  6.  * | |           |              |     ------------------«-----------------------
  7.  * | |           |auto          |     |                                        |
  8.  * | |          \|/    start() \|/   \|/     auto          auto         stop() |
  9.  * | |      INITIALIZED --»-- STARTING_PREP --»- STARTING --»- STARTED --»---  |
  10.  * | |         |                                                            |  |
  11.  * | |destroy()|                                                            |  |
  12.  * | --»-----«--    ------------------------«--------------------------------  ^
  13.  * |     |          |                                                          |
  14.  * |     |         \|/          auto                 auto              start() |
  15.  * |     |     STOPPING_PREP ----»---- STOPPING ------»----- STOPPED -----»-----
  16.  * |    \|/                               ^                     |  ^
  17.  * |     |               stop()           |                     |  |
  18.  * |     |       --------------------------                     |  |
  19.  * |     |       |                                              |  |
  20.  * |     |       |    destroy()                       destroy() |  |
  21.  * |     |    FAILED ----»------ DESTROYING ---«-----------------  |
  22.  * |     |                        ^     |                          |
  23.  * |     |     destroy()          |     |auto                      |
  24.  * |     --------»-----------------    \|/                         |
  25.  * |                                 DESTROYED                     |
  26.  * |                                                               |
  27.  * |                            stop()                             |
  28.  * ----»-----------------------------»------------------------------

生命周期状态图

  1. 当组件在STARTING_PREP、STARTING或STARTED时，调用start()方法没有任何效果
  2. 当组件在NEW状态时，调用start()方法会导致init()方法被立刻执行，随后start()方法被执行
  3. 当组件在STOPPING_PREP、STOPPING或STOPPED时，调用stop()方法没有任何效果
  4. 当一个组件在NEW状态时，调用stop()方法会将组件状态变更为STOPPED，比较典型的场景就是组件启动失败，其子组件还没有启动。当一个组件停止的时候，它将尝试停止它下面的所有子组件，即使子组件还没有启动。

Lifecycle中的方法

Lifecycle有哪些方法，如下所示：

  1. public interface Lifecycle {
  2.     // 添加监听器
  3.     public void addLifecycleListener(LifecycleListener listener);
  4.     // 获取所以监听器
  5.     public LifecycleListener[] findLifecycleListeners();
  6.     // 移除某个监听器
  7.     public void removeLifecycleListener(LifecycleListener listener);
  8.     // 初始化方法
  9.     public void init() throws LifecycleException;
  10.     // 启动方法
  11.     public void start() throws LifecycleException;
  12.     // 停止方法，和start对应
  13.     public void stop() throws LifecycleException;
  14.     // 销毁方法，和init对应
  15.     public void destroy() throws LifecycleException;
  16.     // 获取生命周期状态
  17.     public LifecycleState getState();
  18.     // 获取字符串类型的生命周期状态
  19.     public String getStateName();
  20. }

这些方法基本上都会抛出异常-LifecycleException。同时这些方法都非常简单，也很容易懂，在此不再赘述。

LifecycleBase

LifecycleBase是Lifecycle的基本实现。看下Lifecycle中的方法。

1.增加、删除和获取监听器

  1. private final List<LifecycleListener> lifecycleListeners = new CopyOnWriteArrayList<>();
  3. @Override
  4. public void addLifecycleListener(LifecycleListener listener) {
  5.     lifecycleListeners.add(listener);
  6. }
  7. @Override
  8. public LifecycleListener[] findLifecycleListeners() {
  9.     return lifecycleListeners.toArray(new LifecycleListener[0]);
  10. }
  11. @Override
  12. public void removeLifecycleListener(LifecycleListener listener) {
  13.     lifecycleListeners.remove(listener);
  14. }
  1. 生命周期监听器保存在一个线程安全的List中，CopyOnWriteArrayList。所以add和remove都是直接调用此List的相应方法。
  2. 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。

2.init()

  1. @Override
  2. public final synchronized void init() throws LifecycleException {
  3.     // 非NEW状态，不允许调用init()方法
  4.     if (!state.equals(LifecycleState.NEW)) {
  5.         invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
  6.     }
  8.     try {
  9.         // 初始化逻辑之前，先将状态变更为`INITIALIZING`
  10.         setStateInternal(LifecycleState.INITIALIZING, null, false);
  11.         // 初始化，该方法为一个abstract方法，需要组件自行实现
  12.         initInternal();
  13.         // 初始化完成之后，状态变更为`INITIALIZED`
  14.         setStateInternal(LifecycleState.INITIALIZED, null, false);
  15.     } catch (Throwable t) {
  16.         // 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`
  17.         ExceptionUtils.handleThrowable(t);
  18.         setStateInternal(LifecycleState.FAILED, null, false);
  19.         throw new LifecycleException(
  20.                 sm.getString("lifecycleBase.initFail",toString()), t);
  21.     }
  22. }

再来看看invalidTransition方法，该方法直接抛出异常。

  1. private void invalidTransition(String type) throws LifecycleException {
  2.     String msg = sm.getString("lifecycleBase.invalidTransition", type,
  3.             toString(), state);
  4.     throw new LifecycleException(msg);
  5. }

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。

private volatile LifecycleState state = LifecycleState.NEW;。

  1. private synchronized void setStateInternal(LifecycleState state,
  2.         Object data, boolean check) throws LifecycleException {
  3.     if (log.isDebugEnabled()) {
  4.         log.debug(sm.getString("lifecycleBase.setState", this, state));
  5.     }
  7.     // 是否校验状态
  8.     if (check) {
  9.         // Must have been triggered by one of the abstract methods (assume
  10.         // code in this class is correct)
  11.         // null is never a valid state
  12.         // state不允许为null
  13.         if (state == null) {
  14.             invalidTransition("null");
  15.             // Unreachable code - here to stop eclipse complaining about
  16.             // a possible NPE further down the method
  17.             return;
  18.         }
  20.         // Any method can transition to failed
  21.         // startInternal() permits STARTING_PREP to STARTING
  22.         // stopInternal() permits STOPPING_PREP to STOPPING and FAILED to
  23.         // STOPPING
  24.         if (!(state == LifecycleState.FAILED ||
  25.                 (this.state == LifecycleState.STARTING_PREP &&
  26.                         state == LifecycleState.STARTING) ||
  27.                 (this.state == LifecycleState.STOPPING_PREP &&
  28.                         state == LifecycleState.STOPPING) ||
  29.                 (this.state == LifecycleState.FAILED &&
  30.                         state == LifecycleState.STOPPING))) {
  31.             // No other transition permitted
  32.             invalidTransition(state.name());
  33.         }
  34.     }
  36.     // 设置状态
  37.     this.state = state;
  38.     // 触发事件
  39.     String lifecycleEvent = state.getLifecycleEvent();
  40.     if (lifecycleEvent != null) {
  41.         fireLifecycleEvent(lifecycleEvent, data);
  42.     }
  43. }

3.start()

  1. @Override
  2. public final synchronized void start() throws LifecycleException {
  3.     // `STARTING_PREP`、`STARTING`和`STARTED时，将忽略start()逻辑
  4.     if (LifecycleState.STARTING_PREP.equals(state) || LifecycleState.STARTING.equals(state) ||
  5.             LifecycleState.STARTED.equals(state)) {
  7.         if (log.isDebugEnabled()) {
  8.             Exception e = new LifecycleException();
  9.             log.debug(sm.getString("lifecycleBase.alreadyStarted", toString()), e);
  10.         } else if (log.isInfoEnabled()) {
  11.             log.info(sm.getString("lifecycleBase.alreadyStarted", toString()));
  12.         }
  14.         return;
  15.     }
  17.     // `NEW`状态时，执行init()方法
  18.     if (state.equals(LifecycleState.NEW)) {
  19.         init();
  20.     }
  22.     // `FAILED`状态时，执行stop()方法
  23.     else if (state.equals(LifecycleState.FAILED)) {
  24.         stop();
  25.     }
  27.     // 不是`INITIALIZED`和`STOPPED`时，则说明是非法的操作
  28.     else if (!state.equals(LifecycleState.INITIALIZED) &&
  29.             !state.equals(LifecycleState.STOPPED)) {
  30.         invalidTransition(Lifecycle.BEFORE_START_EVENT);
  31.     }
  33.     try {
  34.         // start前的状态设置
  35.         setStateInternal(LifecycleState.STARTING_PREP, null, false);
  36.         // start逻辑，抽象方法，由组件自行实现
  37.         startInternal();
  38.         // start过程中，可能因为某些原因失败，这时需要stop操作
  39.         if (state.equals(LifecycleState.FAILED)) {
  40.             // This is a 'controlled' failure. The component put itself into the
  41.             // FAILED state so call stop() to complete the clean-up.
  42.             stop();
  43.         } else if (!state.equals(LifecycleState.STARTING)) {
  44.             // Shouldn't be necessary but acts as a check that sub-classes are
  45.             // doing what they are supposed to.
  46.             invalidTransition(Lifecycle.AFTER_START_EVENT);
  47.         } else {
  48.             // 设置状态为STARTED
  49.             setStateInternal(LifecycleState.STARTED, null, false);
  50.         }
  51.     } catch (Throwable t) {
  52.         // This is an 'uncontrolled' failure so put the component into the
  53.         // FAILED state and throw an exception.
  54.         ExceptionUtils.handleThrowable(t);
  55.         setStateInternal(LifecycleState.FAILED, null, false);
  56.         throw new LifecycleException(sm.getString("lifecycleBase.startFail", toString()), t);
  57.     }
  58. }

4.stop()

  1. @Override
  2. public final synchronized void stop() throws LifecycleException {
  3.     // `STOPPING_PREP`、`STOPPING`和STOPPED时，将忽略stop()的执行
  4.     if (LifecycleState.STOPPING_PREP.equals(state) || LifecycleState.STOPPING.equals(state) ||
  5.             LifecycleState.STOPPED.equals(state)) {
  7.         if (log.isDebugEnabled()) {
  8.             Exception e = new LifecycleException();
  9.             log.debug(sm.getString("lifecycleBase.alreadyStopped", toString()), e);
  10.         } else if (log.isInfoEnabled()) {
  11.             log.info(sm.getString("lifecycleBase.alreadyStopped", toString()));
  12.         }
  14.         return;
  15.     }
  17.     // `NEW`状态时，直接将状态变更为`STOPPED`
  18.     if (state.equals(LifecycleState.NEW)) {
  19.         state = LifecycleState.STOPPED;
  20.         return;
  21.     }
  23.     // stop()的执行，必须要是`STARTED`和`FAILED`
  24.     if (!state.equals(LifecycleState.STARTED) && !state.equals(LifecycleState.FAILED)) {
  25.         invalidTransition(Lifecycle.BEFORE_STOP_EVENT);
  26.     }
  28.     try {
  29.         // `FAILED`时，直接触发BEFORE_STOP_EVENT事件
  30.         if (state.equals(LifecycleState.FAILED)) {
  31.             // Don't transition to STOPPING_PREP as that would briefly mark the
  32.             // component as available but do ensure the BEFORE_STOP_EVENT is
  33.             // fired
  34.             fireLifecycleEvent(BEFORE_STOP_EVENT, null);
  35.         } else {
  36.             // 设置状态为STOPPING_PREP
  37.             setStateInternal(LifecycleState.STOPPING_PREP, null, false);
  38.         }
  40.         // stop逻辑，抽象方法，组件自行实现
  41.         stopInternal();
  43.         // Shouldn't be necessary but acts as a check that sub-classes are
  44.         // doing what they are supposed to.
  45.         if (!state.equals(LifecycleState.STOPPING) && !state.equals(LifecycleState.FAILED)) {
  46.             invalidTransition(Lifecycle.AFTER_STOP_EVENT);
  47.         }
  48.         // 设置状态为STOPPED
  49.         setStateInternal(LifecycleState.STOPPED, null, false);
  50.     } catch (Throwable t) {
  51.         ExceptionUtils.handleThrowable(t);
  52.         setStateInternal(LifecycleState.FAILED, null, false);
  53.         throw new LifecycleException(sm.getString("lifecycleBase.stopFail",toString()), t);
  54.     } finally {
  55.         if (this instanceof Lifecycle.SingleUse) {
  56.             // Complete stop process first
  57.             setStateInternal(LifecycleState.STOPPED, null, false);
  58.             destroy();
  59.         }
  60.     }
  61. }

5.destroy()

  1. @Override
  2. public final synchronized void destroy() throws LifecycleException {
  3.     // `FAILED`状态时，直接触发stop()逻辑
  4.     if (LifecycleState.FAILED.equals(state)) {
  5.         try {
  6.             // Triggers clean-up
  7.             stop();
  8.         } catch (LifecycleException e) {
  9.             // Just log. Still want to destroy.
  10.             log.warn(sm.getString(
  11.                     "lifecycleBase.destroyStopFail", toString()), e);
  12.         }
  13.     }
  15.     // `DESTROYING`和`DESTROYED`时，忽略destroy的执行
  16.     if (LifecycleState.DESTROYING.equals(state) ||
  17.             LifecycleState.DESTROYED.equals(state)) {
  19.         if (log.isDebugEnabled()) {
  20.             Exception e = new LifecycleException();
  21.             log.debug(sm.getString("lifecycleBase.alreadyDestroyed", toString()), e);
  22.         } else if (log.isInfoEnabled() && !(this instanceof Lifecycle.SingleUse)) {
  23.             // Rather than have every component that might need to call
  24.             // destroy() check for SingleUse, don't log an info message if
  25.             // multiple calls are made to destroy()
  26.             log.info(sm.getString("lifecycleBase.alreadyDestroyed", toString()));
  27.         }
  29.         return;
  30.     }
  32.     // 非法状态判断
  33.     if (!state.equals(LifecycleState.STOPPED) &&
  34.             !state.equals(LifecycleState.FAILED) &&
  35.             !state.equals(LifecycleState.NEW) &&
  36.             !state.equals(LifecycleState.INITIALIZED)) {
  37.         invalidTransition(Lifecycle.BEFORE_DESTROY_EVENT);
  38.     }
  40.     try {
  41.         // destroy前状态设置
  42.         setStateInternal(LifecycleState.DESTROYING, null, false);
  43.        // 抽象方法，组件自行实现
  44.         destroyInternal();
  45.         // destroy后状态设置
  46.         setStateInternal(LifecycleState.DESTROYED, null, false);
  47.     } catch (Throwable t) {
  48.         ExceptionUtils.handleThrowable(t);
  49.         setStateInternal(LifecycleState.FAILED, null, false);
  50.         throw new LifecycleException(
  51.                 sm.getString("lifecycleBase.destroyFail",toString()), t);
  52.     }
  53. }

6.模板方法

从上述源码看得出来，LifecycleBase是使用了状态机+模板模式来实现的。模板方法有下面这几个：

  1. // 初始化方法
  2. protected abstract void initInternal() throws LifecycleException;
  3. // 启动方法
  4. protected abstract void startInternal() throws LifecycleException;
  5. // 停止方法
  6. protected abstract void stopInternal() throws LifecycleException;
  7. // 销毁方法
  8. protected abstract void destroyInternal() throws LifecycleException;

tomcat启动图

Tomcat-Lifecycle - 图1