tomcat 7 源码分析-8 生命周期lifecycle和监听listener

ezeke

　　每个应用都有生命周期lifecycle，可能包括init,start,stop,destroy等更多。针对生命周期的变化，如何做变化作出反应，tomcat在设计的时候，把时间监听listener结合起来，所以listener取的名字是lifecyclelistener，对lifecycle进行监听。
　　总的最底层的来自两个interface的设计Lifecycle和LifecycleListener。
　　lifecycle这个接口定义了除本身生命周期的函数，另外还定义了整个生命周期阶段的事件类型(这个肯定是为lifecyclelistener准备的)，同时还对LifecycleListener有增加，删除，通知等的函数。LifecycleListener这个接口定义了对事件Event的反应。简单看下Lifecycle和LifecycleListener的代码片段。

public interface Lifecycle {
/**
* The LifecycleEvent type for the "component init" event.
*/
public static final String INIT_EVENT = "init";

/**
* The LifecycleEvent type for the "component start" event.
*/
public static final String START_EVENT = "start";

/**
* The LifecycleEvent type for the "component before start" event.
*/
public static final String BEFORE_START_EVENT = "before_start";
[..........]
// --------------------------------------------------------- Public Methods

/**
* Add a LifecycleEvent listener to this component.
*
* @param listener The listener to add
*/
public void addLifecycleListener(LifecycleListener listener);

/**
* Get the lifecycle listeners associated with this lifecycle. If this
* Lifecycle has no listeners registered, a zero-length array is returned.
*/
public LifecycleListener[] findLifecycleListeners();
[.............]
public void init() throws LifecycleException;
public void start() throws LifecycleException;
public void stop() throws LifecycleException;
public void destroy() throws LifecycleException;
public LifecycleState getState();
}
 
public interface LifecycleListener {

/**
* Acknowledge the occurrence of the specified event.
*
* @param event LifecycleEvent that has occurred
*/
public void lifecycleEvent(LifecycleEvent event);

}
　　后续的问题是，谁来维护LifecycleListener？谁维护LifecycleListener，必然要提供真正意思上对操作(增，删，查和通知)函数。Tomcat将这些交给了LifecycleSupport。同时LifecycleSupport还提供对lifecycle传来的bype，data封装成
　　LifecycleEvent类，给LifecycleListener用。

public final class LifecycleSupport {
public LifecycleSupport(Lifecycle lifecycle) {
super();
this.lifecycle = lifecycle;
}
private Lifecycle lifecycle = null;
private LifecycleListener listeners[] = new LifecycleListener[0];
private final Object listenersLock = new Object(); // Lock object for changes to listeners
public void addLifecycleListener(LifecycleListener listener) {
synchronized (listenersLock) {
LifecycleListener results[] =
new LifecycleListener[listeners.length + 1];
for (int i = 0; i < listeners.length; i++)
results = listeners;
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[] = listeners;
for (int i = 0; i < interested.length; i++)
interested.lifecycleEvent(event);
}
public void removeLifecycleListener(LifecycleListener listener) {
synchronized (listenersLock) {
int n = -1;
for (int i = 0; i < listeners.length; i++) {
if (listeners == 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;
}
listeners = results;
}
}

}
　　tomcat的应用都继承之Lifecycle，包括server，service，Connector，GlobalNamingResources等，而针对这些又实现不同的LifecycleListener。