Nacos server事件分发EventDispatcher代码小结

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我是靠谱客的博主安静冬日，最近开发中收集的这篇文章主要介绍Nacos server事件分发EventDispatcher代码小结，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

EventDispatcher类，作为事件分发器。

AbstractEventListener静态内部抽象类，继承该类后实例化的子类，将在该类中的构造方法被注册到EventDispatcher中，这一点以前我没有想到，挺好的写法，设计模式是监听器模式，通过事件调用具体事件的监听类。对于Spring监听器的实现也是类似，只不过spring监听器将事件作为参数与监听器绑定，通过监听器轮询反射获取参数类型进行比对，而nacos事件分发监听是直接通过监听器与事件类进行成员变量的绑定，注册监听事件的过程有点绕，过程总结如下：

实例化子类监听器-》注册子类监听器，注册过程同时要调用子类监听器的interest方法，返回事件类型，将事件类型与监听器进行多对一的注册Entry入口中

 /**
* add event listener
*/
static public void addEventListener(AbstractEventListener listener) {
for (Class<? extends Event> type : listener.interest()) {
getEntry(type).listeners.addIfAbsent(listener);
}
}

Entry类的成员变量：
final Class<? extends Event> eventType;
final CopyOnWriteArrayList<AbstractEventListener> listeners;

static Entry getEntry(Class<? extends Event> eventType) {
for (; ; ) {
for (Entry entry : LISTENER_HUB) {
if (entry.eventType == eventType) {
return entry;
}
}
Entry tmp = new Entry(eventType);
/**
*
false means already exists
*/
if (LISTENER_HUB.addIfAbsent(tmp)) {
return tmp;
}
}
}

使用过程通过调用：

EventDispatcher.fireEvent(new ConfigDataChangeEvent(false, dataId, group, tenant, time.getTime()));

/**
* fire event, notify listeners.
*/
static public void fireEvent(Event event) {
if (null == event) {
throw new IllegalArgumentException();
}
for (AbstractEventListener listener : getEntry(event.getClass()).listeners) {
try {
listener.onEvent(event);
} catch (Exception e) {
log.error(e.toString(), e);
}
}
}

完整事件分配的代码：


public class EventDispatcher {
/**
* add event listener
*/
static public void addEventListener(AbstractEventListener listener) {
for (Class<? extends Event> type : listener.interest()) {
getEntry(type).listeners.addIfAbsent(listener);
}
}
/**
* fire event, notify listeners.
*/
static public void fireEvent(Event event) {
if (null == event) {
throw new IllegalArgumentException();
}
for (AbstractEventListener listener : getEntry(event.getClass()).listeners) {
try {
listener.onEvent(event);
} catch (Exception e) {
log.error(e.toString(), e);
}
}
}
/**
* For only test purpose
*/
static public void clear() {
LISTENER_HUB.clear();
}
/**
* get event listener for eventType. Add Entry if not exist.
*/
static Entry getEntry(Class<? extends Event> eventType) {
for (; ; ) {
for (Entry entry : LISTENER_HUB) {
if (entry.eventType == eventType) {
return entry;
}
}
Entry tmp = new Entry(eventType);
/**
*
false means already exists
*/
if (LISTENER_HUB.addIfAbsent(tmp)) {
return tmp;
}
}
}
static private class Entry {
final Class<? extends Event> eventType;
final CopyOnWriteArrayList<AbstractEventListener> listeners;
Entry(Class<? extends Event> type) {
eventType = type;
listeners = new CopyOnWriteArrayList<AbstractEventListener>();
}
@Override
public boolean equals(Object obj) {
if (null == obj || obj.getClass() != getClass()) {
return false;
}
if (this == obj) {
return true;
}
return eventType == ((Entry)obj).eventType;
}
@Override
public int hashCode() {
return super.hashCode();
}
}
static private final Logger log = LoggerFactory.getLogger(EventDispatcher.class);
static final CopyOnWriteArrayList<Entry> LISTENER_HUB = new CopyOnWriteArrayList<Entry>();
public interface Event {
}
static public abstract class AbstractEventListener {
public AbstractEventListener() {
/**
* automatic register
*/
EventDispatcher.addEventListener(this);
}
/**
* 感兴趣的事件列表
*
* @return event list
*/
abstract public List<Class<? extends Event>> interest();
/**
* 处理事件
*
* @param event event
*/
abstract public void onEvent(Event event);
}
}