Tomcat监听器设计思路-白红宇

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;}复制代码

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);}复制代码

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;        }    }}复制代码