How Tomcat Works （6）生命周期Lifecycle
总体概述
这一章讲的是tomcat的组件之一，LifeCycle组件，通过这个组件可以统一管理其他组件，可以达到统一启动/关闭组件的目的，那么LifeCycle是如何实现看似如此神奇的功能的呢？
实现了LifeCycle接口的组件，可以触发如下的事件
- BEFORE_START_EVENT
- START_EVENT
- AFTER_START_EVENT
- BEFORE_STOP_EVENT
- STOP_EVENT
- AFTER_STOP_EVENT
而事件监听器LifeCycleListener，它监听到这些事件然后做出响应的举动，在这里就可以去统一的开启/关闭容器
主要类以及接口
LifeCycle接口
public interface Lifecycle {
/**
* The LifecycleEvent type for the "component start" event.
*/
//start事件,其实它就是个字符串
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";
//添加Listener
public void addLifecycleListener(LifecycleListener listener);
//返回实现了这个接口的容器所绑定的listener
public LifecycleListener[] findLifecycleListeners();
//移除某个listener
public void removeLifecycleListener(LifecycleListener listener);
//lifecycle接口最重要的两个方法，组件必须提供这两个方法的实现，以供父组件调用，
//实现父组件对于子组件的开启/关闭
public void start() throws LifecycleException;
public void stop() throws LifecycleException;
}
LifeEvent类
生命周期事件是org.apache.catalina.LifecycleEvent类的实例，其实这个类也很简单，对于上面的String进行了一些包装，添加了一些额外的属性而已，类定义如下
public final class LifecycleEvent
extends EventObject {
private Object data = null;
private Lifecycle lifecycle = null;
//这里的type就对应lifecycle中定义的那6个事件
private String type = null;
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;
}
public Object getData() {
return (this.data);
}
public Lifecycle getLifecycle() {
return (this.lifecycle);
}
public String getType() {
return (this.type);
}
}