Tomcat中Lifecycle详解（源码阅读）

        在tomcat中，每一个组件生命周期都是需要统一管理的，一般是由调用该组件的组件来启动或停止当前组建，如connector组件控制processor组件启动和停止，因此每个组件主要类都会继承Lifecycle接口。tomcat中周期控制采用观察者模式来设计。其中主要类和接口如下：

1. Lifecycle接口（要使用生命周期控制的类都会继承该类）
2. LifecycleListener接口（监听器都会继承该类）
3. LifecycleSupport类（用来对监听器进行管理）
4. LifecycleEvent类（该类是一个辅助类，用来作为参数类型）
5. LifecycleException类（异常类）

Talk is cheap. Show me the code.

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Lifecycle接口

public interface Lifecycle {    // ----------------------------------------------------- Manifest Constants    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 Methods    public void addLifecycleListener(LifecycleListener listener);    public LifecycleListener[] findLifecycleListeners();    public void removeLifecycleListener(LifecycleListener listener);    public void start() throws LifecycleException;    public void stop() throws LifecycleException;}

LifecycleListener接口

public interface LifecycleListener {    public void lifecycleEvent(LifecycleEvent event);}

LifecycleSupport类
该类是一种中间类，主要目的就是对LifecycleListener[]数组进行管理。而且

public final class LifecycleSupport {    // ----------------------------------------------------------- Constructors        public LifecycleSupport(Lifecycle lifecycle) {        super();        this.lifecycle = lifecycle;    }    // ----------------------------------------------------- Instance Variables    private Lifecycle lifecycle = null;    private LifecycleListener listeners[] = new LifecycleListener[0];    // --------------------------------------------------------- Public Methods    //添加监听器，该方法中动态数组的方法值得借鉴    public void addLifecycleListener(LifecycleListener listener) {      synchronized (listeners) {          LifecycleListener results[] =            new LifecycleListener[listeners.length + 1];          for (int i = 0; i < listeners.length; i++)              results[i] = listeners[i];          results[listeners.length] = listener;          listeners = results;      }    }    public LifecycleListener[] findLifecycleListeners() {        return listeners;    }    public void fireLifecycleEvent(String type, Object data) {        LifecycleEvent event = new LifecycleEvent(lifecycle, type, data);        LifecycleListener interested[] = null;        synchronized (listeners) {            interested = (LifecycleListener[]) listeners.clone();        }        for (int i = 0; i < interested.length; i++)            interested[i].lifecycleEvent(event);    }    public void removeLifecycleListener(LifecycleListener listener) {        synchronized (listeners) {            int n = -1;            for (int i = 0; i < listeners.length; i++) {                if (listeners[i] == listener) {                    n = i;                    break;                }            }            if (n < 0)                return;            LifecycleListener results[] =              new LifecycleListener[listeners.length - 1];            int j = 0;            for (int i = 0; i < listeners.length; i++) {                if (i != n)                    results[j++] = listeners[i];            }            listeners = results;        }    }}

LifecycleEvent类
该类是一个辅助类，用来 lifecycleEvent(LifecycleEvent event)方法的参数类型。

public final class LifecycleEvent extends EventObject {    // ----------------------------------------------------------- Constructors    public LifecycleEvent(Lifecycle lifecycle, String type) {        this(lifecycle, type, null);    }    public LifecycleEvent(Lifecycle lifecycle, String type, Object data) {        super(lifecycle);        this.lifecycle = lifecycle;        this.type = type;        this.data = data;    }    // ----------------------------------------------------- Instance Variables    private Object data = null;    private Lifecycle lifecycle = null;    private String type = null;    // ------------------------------------------------------------- Properties    public Object getData() {        return (this.data);    }    public Lifecycle getLifecycle() {        return (this.lifecycle);    }    public String getType() {        return (this.type);    }}

LifecycleException类
该类只是一个异常类，该处代码省略。

connector中的实际调用

如tomcat4中connector组件的默认实现类HttpConnector就实现了Lifecycle接口，如下所示

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public final class HttpConnector implements Connector, Lifecycle, Runnable{//实例化一个LifecycleSupport 类，用来管理监听器的注册和取消。protected LifecycleSupport lifecycle = new LifecycleSupport(this);public void addLifecycleListener(LifecycleListener listener) {        lifecycle.addLifecycleListener(listener);    }    public LifecycleListener[] findLifecycleListeners() {        return lifecycle.findLifecycleListeners();    }    public void removeLifecycleListener(LifecycleListener listener) {        lifecycle.removeLifecycleListener(listener);    }public void start() throws LifecycleException {        // Validate and update our current state        if (started)            throw new LifecycleException                (sm.getString("httpConnector.alreadyStarted"));        threadName = "HttpConnector[" + port + "]";        //激活监听器，该方法会调用各个监听器的lifecycleEvent（）方法。        lifecycle.fireLifecycleEvent(START_EVENT, null);        started = true;/*        // Start our background thread        threadStart();        // Create the specified minimum number of processors        while (curProcessors < minProcessors) {            if ((maxProcessors > 0) && (curProcessors >= maxProcessors))                break;            HttpProcessor processor = newProcessor();            recycle(processor);        }*/    }    public void stop() throws LifecycleException {        // Validate and update our current state        if (!started)            throw new LifecycleException                (sm.getString("httpConnector.notStarted"));        lifecycle.fireLifecycleEvent(STOP_EVENT, null);        started = false;        // Gracefully shut down all processors we have created        for (int i = created.size() - 1; i >= 0; i--) {            HttpProcessor processor = (HttpProcessor) created.elementAt(i);            if (processor instanceof Lifecycle) {                try {                    ((Lifecycle) processor).stop();                } catch (LifecycleException e) {                    log("HttpConnector.stop", e);                }            }        }      /*  synchronized (threadSync) {            // Close the server socket we were using            if (serverSocket != null) {                try {                    serverSocket.close();                } catch (IOException e) {                    ;                }            }            // Stop our background thread            threadStop();        }        serverSocket = null;    }*/}