【知识库】–Dubbo ReferenceBean获取 — 源码过程（254）

此段分析的由来：

     <dubbo:reference/> 自定义标签被spring加载时生成ReferenceBean，而ReferenceBean类的定义

public class ReferenceBean<T> extends ReferenceConfig<T> implements FactoryBean, ApplicationContextAware, InitializingBean, DisposableBean 

看到实现了spring的FactoryBean 他有一个接口用来获取代理对象：getObject().其实对于dubbo来说就是生成对远程服务调用的代理。

public Object getObject() throws Exception {
    return get();
}

继续调用

ReferenceConfig

public synchronized T get() {
    if (destroyed) {
        throw new IllegalStateException("Already destroyed!");
    }
    if (ref == null) {
        init();
    }
    return ref;
}

继续调用：

private void init() {
    if (initialized) {
        return;
    }
    checkAndLoadConfig();
    ref = createProxy();
    initialized = true;
}

@SuppressWarnings({
 
 "unchecked", "rawtypes", "deprecation"})
private T createProxy() {
    URL tmpUrl = new URL("temp", "localhost", 0, initedParameterMap);
    if (isJvmRefer(tmpUrl)) {
        URL url = new URL(Constants.LOCAL_PROTOCOL, NetUtils.LOCALHOST, 0, interfaceClass.getName()).addParameters(initedParameterMap);
        invoker = refprotocol.refer(interfaceClass, url);
        if (logger.isInfoEnabled()) {
            logger.info("Using injvm service " + interfaceClass.getName());
        }
    } else {
        urls.addAll(getInvokerUrls());//获取registryUrls
        invoker = getClusterInvoker(urls);//伪装策略
    }
    Boolean c = check;
    if (c == null && consumer != null) {
        c = consumer.isCheck();
    }
    if (c == null) {
        c = true; // default true
    }
    if (c && !invoker.isAvailable()) {
        throw new IllegalStateException("Failed to check the status of the service " + interfaceName + ". No provider available for the service " + (group == null ? "" : group + "/") + interfaceName + (version == null ? "" : ":" + version) + " from the url " + invoker.getUrl() + " to the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion());
    }
    if (logger.isInfoEnabled()) {
        logger.info("Refer dubbo service " + interfaceClass.getName() + " from url " + invoker.getUrl());
    }
    // 创建服务代理
    return (T) proxyFactory.getProxy(invoker);
}

private List<URL> getInvokerUrls() {
    List<URL> urlList = Lists.newArrayList();
    if (url != null && url.length() > 0) { // 用户指定URL，指定的URL可能是对点对直连地址，也可能是注册中心URL
        String[] us = Constants.SEMICOLON_SPLIT_PATTERN.split(url);
        if (us != null && us.length > 0) {
            for (String u : us) {
                URL url = URL.valueOf(u);
                if (url.getPath() == null || url.getPath().length() == 0) {
                    url = url.setPath(interfaceName);
                }
                if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
                    urlList.add(url.addParameterAndEncoded(Constants.REFER_KEY, StringUtils.toQueryString(initedParameterMap)));
                } else {
                    urlList.add(ClusterUtils.mergeUrl(url, initedParameterMap));//此处应该是不是dubbo://127.0.0.1:20880...等待debug
                }
            }
        }
    } else { // 通过注册中心配置拼装URL
        List<URL> us = loadRegistries(false);
        if (us != null && us.size() > 0) {
            for (URL u : us) {
                URL monitorUrl = loadMonitor(u);
                if (monitorUrl != null) {
                    initedParameterMap.put(Constants.MONITOR_KEY, URL.encode(monitorUrl.toFullString()));
                }
                Map<String, String> params = Maps.newHashMap(this.initedParameterMap);
                String quota = u.getParameter(Constants.REGISTRY_WEIGHT_KEY);
                if (!Strings.isNullOrEmpty(quota)) {
                    params.put(Constants.REGISTRY_WEIGHT_KEY, quota);
                }
                String unit = u.getParameter(Constants.QDUBBO_UNIT);
                if (!Strings.isNullOrEmpty(unit)) {
                    params.put(Constants.QDUBBO_UNIT, unit);
                }
                urlList.add(u.removeParameter(Constants.REGISTRY_WEIGHT_KEY).addParameterAndEncoded(Constants.REFER_KEY,  StringUtils.toQueryString(params))); //增加REFER_KEY = "refer"; 结果例如registry://127.0.0.1:9098/com.alibaba.dubbo.registry.RegistryService?application=demo-consumer&dubbo=2.0.0&pid=2484&refer=application%3Ddemo-consumer ...
            }
        }
        if (urlList.isEmpty()) {
            throw new IllegalStateException("No such any registry to reference " + interfaceName + " on the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion() + ", please config <dubbo:registry address=\"...\" /> to your spring config.");
        }
    }
    return urlList;
}

跟进 — getClusterInvoker(urls);

@SuppressWarnings("unchecked")
private Invoker<?> getClusterInvoker(List<URL> urls) {
    List<Invoker<?>> invokers = new ArrayList<Invoker<?>>();
    URL registryURL = null;
    for (URL url : urls) {
        invokers.add(refprotocol.refer(interfaceClass, url));       //SPI扩展接口自适应获取invoker
        if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {// 注册中心协议  REGISTRY_PROTOCOL = "registry";

            registryURL = url; // 用了最后一个registry url
        }
    }
    if (registryURL != null) { // 有 注册中心协议的URL
        if (useUnitCluster()) {
            URL u = registryURL.addParameterIfAbsent(Constants.REGISTRY_KEY + "." + Constants.CLUSTER_KEY, FailfastCluster.NAME);
            return registryCluster.join(new UnitDirectory(u, invokers));
        } else {
            URL u = registryURL.addParameterIfAbsent(Constants.REGISTRY_KEY + "." + Constants.CLUSTER_KEY, AvailableCluster.NAME);//默认是用available策略    伪装成一个invoker    
            return registryCluster.join(new StaticDirectory(u, invokers));
        }
    } else { // 不是 注册中心的URL
        return cluster.join(new StaticDirectory(invokers));
    }
}

最后使用代理工厂创建–代理T

// 创建服务代理
return (T) proxyFactory.getProxy(invoker);