监听器顾名思义监听某个事件。那肯定包含一个发事件的东西和一个监听到事件时，作出相应的处理动作。
发事件，那么就要定义一些事件(常量)。
监听事件，那么就要设计一些监听器，然后把它存储起来。
在Tomcat中具体涉及到以下接口:
顶层接口Lifecycle
public interface Lifecycle {
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 void addLifecycleListener(LifecycleListener listener);
public LifecycleListener[] findLifecycleListeners();
public void removeLifecycleListener(LifecycleListener listener);
public void start() throws LifecycleException;
public void stop() throws LifecycleException;
}
监听器接口LifecycleListener
public interface LifecycleListener {
//自定义的监听器要实现这个接口
public void lifecycleEvent(LifecycleEvent event);
}
Tomcat自己提供了一个工具类LifecycleSupport来把上面的给关联起来.
public final class LifecycleSupport {
public LifecycleSupport(Lifecycle lifecycle) {
super();
this.lifecycle = lifecycle;
}
private Lifecycle lifecycle = null;
*///存储了所有的监听器
private LifecycleListener listeners[] = new LifecycleListener[0];
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();
}
//给所有的监听器 都发送这个事件
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;
}
}
}
