序

本文主要研究一下nacos config的EventDispatcher

EventDispatcher

nacos-1.1.3/config/src/main/java/com/alibaba/nacos/config/server/utils/event/EventDispatcher.java

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 final Logger log = LoggerFactory.getLogger(EventDispatcher.class);    static final CopyOnWriteArrayList<Entry> LISTENER_HUB = new CopyOnWriteArrayList<Entry>();    public interface Event {    }    //......}
  • EventDispatcher定义了addEventListener、fireEvent、clear方法；addEventListener会添加listener到Entry；fireEvent会遍历指定event的listener然后回调其onEvent方法；clear会清空整个LISTENER_HUB

Entry

nacos-1.1.3/config/src/main/java/com/alibaba/nacos/config/server/utils/event/EventDispatcher.java

    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();        }    }
  • Entry有个eventType属性以及AbstractEventListener类型的listener集合

AbstractEventListener

nacos-1.1.3/config/src/main/java/com/alibaba/nacos/config/server/utils/event/EventDispatcher.java

    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);    }
  • AbstractEventListener定义了interest、onEvent方法

小结

EventDispatcher定义了addEventListener、fireEvent、clear方法；addEventListener会添加listener到Entry；fireEvent会遍历指定event的listener然后回调其onEvent方法；clear会清空整个LISTENER_HUB

doc

  • EventDispatcher