NacosNamingService中subscribe及unsubscribe的原理和使用方法

这篇文章主要讲解了“NacosNamingService中subscribe及unsubscribe的原理和使用方法”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“NacosNamingService中subscribe及unsubscribe的原理和使用方法”吧！

序

本文主要研究一下NacosNamingService的subscribe及unsubscribe

NacosNamingService

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/naming/NacosNamingService.java

public class NacosNamingService implements NamingService {
    private static final String DEFAULT_PORT = "8080";
    private static final long DEFAULT_HEART_BEAT_INTERVAL = TimeUnit.SECONDS.toMillis(5);

    /**
     * Each Naming instance should have different namespace.
     */
    private String namespace;

    private String endpoint;

    private String serverList;

    private String cacheDir;

    private String logName;

    private HostReactor hostReactor;

    private BeatReactor beatReactor;

    private EventDispatcher eventDispatcher;

    private NamingProxy serverProxy;

    //......

    @Override
    public void subscribe(String serviceName, EventListener listener) throws NacosException {
        subscribe(serviceName, new ArrayList<String>(), listener);
    }

    @Override
    public void subscribe(String serviceName, String groupName, EventListener listener) throws NacosException {
        subscribe(serviceName, groupName, new ArrayList<String>(), listener);
    }

    @Override
    public void subscribe(String serviceName, List<String> clusters, EventListener listener) throws NacosException {
        subscribe(serviceName, Constants.DEFAULT_GROUP, clusters, listener);
    }

    @Override
    public void subscribe(String serviceName, String groupName, List<String> clusters, EventListener listener) throws NacosException {
        eventDispatcher.addListener(hostReactor.getServiceInfo(NamingUtils.getGroupedName(serviceName, groupName),
            StringUtils.join(clusters, ",")), StringUtils.join(clusters, ","), listener);
    }

    @Override
    public void unsubscribe(String serviceName, EventListener listener) throws NacosException {
        unsubscribe(serviceName, new ArrayList<String>(), listener);
    }

    @Override
    public void unsubscribe(String serviceName, String groupName, EventListener listener) throws NacosException {
        unsubscribe(serviceName, groupName, new ArrayList<String>(), listener);
    }

    @Override
    public void unsubscribe(String serviceName, List<String> clusters, EventListener listener) throws NacosException {
        unsubscribe(serviceName, Constants.DEFAULT_GROUP, clusters, listener);
    }

    @Override
    public void unsubscribe(String serviceName, String groupName, List<String> clusters, EventListener listener) throws NacosException {
        eventDispatcher.removeListener(NamingUtils.getGroupedName(serviceName, groupName), StringUtils.join(clusters, ","), listener);
    }

    //......
}

• subscribe方法执行eventDispatcher.addListener；unsubscribe方法执行eventDispatcher.removeListener

EventDispatcher

nacos-1.1.3/client/src/main/java/com/alibaba/nacos/client/naming/core/EventDispatcher.java

public class EventDispatcher {

    private ExecutorService executor = null;

    private BlockingQueue<ServiceInfo> changedServices = new LinkedBlockingQueue<ServiceInfo>();

    private ConcurrentMap<String, List<EventListener>> observerMap
        = new ConcurrentHashMap<String, List<EventListener>>();

    public EventDispatcher() {

        executor = Executors.newSingleThreadExecutor(new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                Thread thread = new Thread(r, "com.alibaba.nacos.naming.client.listener");
                thread.setDaemon(true);

                return thread;
            }
        });

        executor.execute(new Notifier());
    }

    public void addListener(ServiceInfo serviceInfo, String clusters, EventListener listener) {

        NAMING_LOGGER.info("[LISTENER] adding " + serviceInfo.getName() + " with " + clusters + " to listener map");
        List<EventListener> observers = Collections.synchronizedList(new ArrayList<EventListener>());
        observers.add(listener);

        observers = observerMap.putIfAbsent(ServiceInfo.getKey(serviceInfo.getName(), clusters), observers);
        if (observers != null) {
            observers.add(listener);
        }

        serviceChanged(serviceInfo);
    }

    public void removeListener(String serviceName, String clusters, EventListener listener) {

        NAMING_LOGGER.info("[LISTENER] removing " + serviceName + " with " + clusters + " from listener map");

        List<EventListener> observers = observerMap.get(ServiceInfo.getKey(serviceName, clusters));
        if (observers != null) {
            Iterator<EventListener> iter = observers.iterator();
            while (iter.hasNext()) {
                EventListener oldListener = iter.next();
                if (oldListener.equals(listener)) {
                    iter.remove();
                }
            }
            if (observers.isEmpty()) {
                observerMap.remove(ServiceInfo.getKey(serviceName, clusters));
            }
        }
    }

    public List<ServiceInfo> getSubscribeServices() {
        List<ServiceInfo> serviceInfos = new ArrayList<ServiceInfo>();
        for (String key : observerMap.keySet()) {
            serviceInfos.add(ServiceInfo.fromKey(key));
        }
        return serviceInfos;
    }

    public void serviceChanged(ServiceInfo serviceInfo) {
        if (serviceInfo == null) {
            return;
        }

        changedServices.add(serviceInfo);
    }

    private class Notifier implements Runnable {
        @Override
        public void run() {
            while (true) {
                ServiceInfo serviceInfo = null;
                try {
                    serviceInfo = changedServices.poll(5, TimeUnit.MINUTES);
                } catch (Exception ignore) {
                }

                if (serviceInfo == null) {
                    continue;
                }

                try {
                    List<EventListener> listeners = observerMap.get(serviceInfo.getKey());

                    if (!CollectionUtils.isEmpty(listeners)) {
                        for (EventListener listener : listeners) {
                            List<Instance> hosts = Collections.unmodifiableList(serviceInfo.getHosts());
                            listener.onEvent(new NamingEvent(serviceInfo.getName(), serviceInfo.getGroupName(), serviceInfo.getClusters(), hosts));
                        }
                    }

                } catch (Exception e) {
                    NAMING_LOGGER.error("[NA] notify error for service: "
                        + serviceInfo.getName() + ", clusters: " + serviceInfo.getClusters(), e);
                }
            }
        }
    }

    public void setExecutor(ExecutorService executor) {
        ExecutorService oldExecutor = this.executor;
        this.executor = executor;

        oldExecutor.shutdown();
    }
}

• EventDispatcher的构造器创建了executor，并执行Notifier；Notifier使用一个while true循环不断执行changedServices.poll(5, TimeUnit.MINUTES)拉取serviceInfo，拉取到的话会从observerMap取出对应的EventListener列表，然后挨个回调listener.onEvent方法

• addListener方法则是往observerMap创建或添加observers，然后执行serviceChanged方法；removeListener则是从observerMap移除指定的listener，如果指定key的listener列表为空则删除该key

• serviceChanged方法会往changedServices添加serviceInfo；之后Notifier异步线程可用拉取信息执行listener.onEvent回调

小结

NacosNamingService的subscribe方法执行eventDispatcher.addListener；unsubscribe方法执行eventDispatcher.removeListener

感谢各位的阅读，以上就是“NacosNamingService中subscribe及unsubscribe的原理和使用方法”的内容了，经过本文的学习后，相信大家对NacosNamingService中subscribe及unsubscribe的原理和使用方法这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是亿速云，小编将为大家推送更多相关知识点的文章，欢迎关注！