在tomcat中，每一個元件生命週期都是需要統一管理的，一般是由呼叫該元件的元件來啟動或停止當前組建，如connector元件控制processor元件啟動和停止，因此每個元件主要類都會繼承Lifecycle介面。tomcat中週期控制採用觀察者模式來設計。其中主要類和介面如下：
- Lifecycle介面（要使用生命週期控制的類都會繼承該類）
- LifecycleListener介面（監聽器都會繼承該類）
- LifecycleSupport類（用來對監聽器進行管理）
- LifecycleEvent類（該類是一個輔助類，用來作為引數型別）
- LifecycleException類（異常類）
Talk is cheap. Show me the code.
Lifecycle介面
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介面
public interface LifecycleListener {
public void lifecycleEvent(LifecycleEvent event);
} LifecycleSupport類
該類是一種中間類，主要目的就是對LifecycleListener[]陣列進行管理。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
//新增監聽器，該方法中動態陣列的方法值得借鑑
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類
該類是一個輔助類，用來 lifecycleEvent(LifecycleEvent event)方法的引數型別。
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類
該類只是一個異常類，該處程式碼省略。
connector中的實際呼叫
如tomcat4中connector元件的預設實現類HttpConnector就實現了Lifecycle介面，如下所示
public final class HttpConnector implements Connector, Lifecycle, Runnable{
//例項化一個LifecycleSupport 類，用來管理監聽器的註冊和取消。
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 + "]";
//啟用監聽器，該方法會呼叫各個監聽器的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;
}*/
}