/**
 * 自适应 Protocol 实现对象
 */
private static final Protocol refprotocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
/**
 * 自适应 ProxyFactory 实现对象
 */
private static final ProxyFactory proxyFactory = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();
    
/**
 * 直连服务提供者地址
 */
// url for peer-to-peer invocation
private String url;

  1: private T createProxy(Map<String, String> map) {
  2:     URL tmpUrl = new URL("temp", "localhost", 0, map);
  3:     // 是否本地引用
  4:     final boolean isJvmRefer;
  5:     // injvm 属性为空，不通过该属性判断
  6:     if (isInjvm() == null) {
  7:         // 直连服务提供者，参见文档《直连提供者》http://dubbo.apache.org/zh-cn/docs/user/demos/explicit-target.html
  8:         if (url != null && url.length() > 0) { // if a url is specified, don't do local reference
  9:             isJvmRefer = false;
 10:         // 通过 `tmpUrl` 判断，是否需要本地引用
 11:         } else if (InjvmProtocol.getInjvmProtocol().isInjvmRefer(tmpUrl)) {
 12:             // by default, reference local service if there is
 13:             isJvmRefer = true;
 14:         // 默认不是
 15:         } else {
 16:             isJvmRefer = false;
 17:         }
 18:     // 通过 injvm 属性。
 19:     } else {
 20:         isJvmRefer = isInjvm();
 21:     }
 22: 
 23:     // 本地引用
 24:     if (isJvmRefer) {
 25:         // 创建服务引用 URL 对象
 26:         URL url = new URL(Constants.LOCAL_PROTOCOL, NetUtils.LOCALHOST, 0, interfaceClass.getName()).addParameters(map);
 27:         // 引用服务，返回 Invoker 对象
 28:         invoker = refprotocol.refer(interfaceClass, url);
 29:         if (logger.isInfoEnabled()) {
 30:             logger.info("Using injvm service " + interfaceClass.getName());
 31:         }
 32:     // 正常流程，一般为远程引用
 33:     } else {
 34:         // ... 省略本文暂时不分享的服务远程引用 
 35:         }
 36:     }
 37: 
 38:     // 启动时检查
 39:     Boolean c = check;
 40:     if (c == null && consumer != null) {
 41:         c = consumer.isCheck();
 42:     }
 43:     if (c == null) {
 44:         c = true; // default true
 45:     }
 46:     if (c && !invoker.isAvailable()) {
 47:         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());
 48:     }
 49:     if (logger.isInfoEnabled()) {
 50:         logger.info("Refer dubbo service " + interfaceClass.getName() + " from url " + invoker.getUrl());
 51:     }
 52: 
 53:     // 创建 Service 代理对象
 54:     // create service proxy
 55:     return (T) proxyFactory.getProxy(invoker);
 56: }

1: public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
2:     // 注册中心
3:     if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
4:         return protocol.refer(type, url);
5:     }
6:     // 引用服务，返回 Invoker 对象
7:     // 给改 Invoker 对象，包装成带有 Filter 过滤链的 Invoker 对象
8:     return buildInvokerChain(protocol.refer(type, url), Constants.REFERENCE_FILTER_KEY, Constants.CONSUMER);
9: }

 1: public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
 2:     // 注册中心协议
 3:     if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
 4:         return protocol.refer(type, url);
 5:     }
 6:     // 引用服务
 7:     Invoker<T> invoker = protocol.refer(type, url);
 8:     // 获得 InvokerListener 数组
 9:     List<InvokerListener> listeners = Collections.unmodifiableList(ExtensionLoader.getExtensionLoader(InvokerListener.class).getActivateExtension(url, Constants.INVOKER_LISTENER_KEY));
10:     // 创建 ListenerInvokerWrapper 对象
11:     return new ListenerInvokerWrapper<T>(invoker, listeners);
12: }

public <T> Invoker<T> refer(Class<T> serviceType, URL url) throws RpcException {
    return new InjvmInvoker<T>(serviceType, url, url.getServiceKey(), exporterMap);
}

/**
 * 接口类型
 */
private final Class<T> type;
/**
 * 服务 URL
 */
private final URL url;
/**
 * 公用的隐式传参。在 {@link #invoke(Invocation)} 方法中使用。
 */
private final Map<String, String> attachment;
/**
 * 是否可用
 */
private volatile boolean available = true;
/**
 * 是否销毁
 */
private AtomicBoolean destroyed = new AtomicBoolean(false);

/**
 * 服务键
 */
private final String key;
/**
 * Exporter 集合
 *
 * key: 服务键
 *
 * 该值实际就是 {@link com.alibaba.dubbo.rpc.protocol.AbstractProtocol#exporterMap}
 */
private final Map<String, Exporter<?>> exporterMap;

InjvmInvoker(Class<T> type, URL url, String key, Map<String, Exporter<?>> exporterMap) {
    super(type, url);
    this.key = key;
    this.exporterMap = exporterMap;
}

@Override
public boolean isAvailable() {
    // 判断是否有 Exporter 对象
    InjvmExporter<?> exporter = (InjvmExporter<?>) exporterMap.get(key);
    if (exporter == null) {
        return false;
    } else {
        return super.isAvailable();
    }
}

public class ListenerInvokerWrapper<T> implements Invoker<T> {

    private static final Logger logger = LoggerFactory.getLogger(ListenerInvokerWrapper.class);

    /**
     * 真实的 Invoker 对象
     */
    private final Invoker<T> invoker;
    /**
     * Invoker 监听器数组
     */
    private final List<InvokerListener> listeners;

    public ListenerInvokerWrapper(Invoker<T> invoker, List<InvokerListener> listeners) {
        if (invoker == null) {
            throw new IllegalArgumentException("invoker == null");
        }
        this.invoker = invoker;
        this.listeners = listeners;
        // 执行监听器
        if (listeners != null && !listeners.isEmpty()) {
            for (InvokerListener listener : listeners) {
                if (listener != null) {
                    try {
                        listener.referred(invoker);
                    } catch (Throwable t) {
                        logger.error(t.getMessage(), t);
                    }
                }
            }
        }
    }

    public Class<T> getInterface() {
        return invoker.getInterface();
    }

    public URL getUrl() {
        return invoker.getUrl();
    }

    public boolean isAvailable() {
        return invoker.isAvailable();
    }

    public Result invoke(Invocation invocation) throws RpcException {
        return invoker.invoke(invocation);
    }

    @Override
    public String toString() {
        return getInterface() + " -> " + (getUrl() == null ? " " : getUrl().toString());
    }

    public void destroy() {
        try {
            invoker.destroy();
        } finally {
            // 执行监听器
            if (listeners != null && !listeners.isEmpty()) {
                for (InvokerListener listener : listeners) {
                    if (listener != null) {
                        try {
                            listener.destroyed(invoker);
                        } catch (Throwable t) {
                            logger.error(t.getMessage(), t);
                        }
                    }
                }
            }
        }
    }

}

@SPI
public interface InvokerListener {

    /**
     * The invoker referred
     *
     * 当服务引用完成
     *
     * @param invoker
     * @throws RpcException
     * @see com.alibaba.dubbo.rpc.Protocol#refer(Class, URL)
     */
    void referred(Invoker<?> invoker) throws RpcException;

    /**
     * The invoker destroyed.
     *
     * 当服务销毁引用完成
     *
     * @param invoker
     * @see com.alibaba.dubbo.rpc.Invoker#destroy()
     */
    void destroyed(Invoker<?> invoker);

}

public abstract class InvokerListenerAdapter implements InvokerListener {

    public void referred(Invoker<?> invoker) throws RpcException { }

    public void destroyed(Invoker<?> invoker) { }

}

@Activate(Constants.DEPRECATED_KEY)
public class DeprecatedInvokerListener extends InvokerListenerAdapter {

    private static final Logger LOGGER = LoggerFactory.getLogger(DeprecatedInvokerListener.class);

    public void referred(Invoker<?> invoker) throws RpcException {
        if (invoker.getUrl().getParameter(Constants.DEPRECATED_KEY, false)) {
            LOGGER.error("The service " + invoker.getInterface().getName() + " is DEPRECATED! Declare from " + invoker.getUrl());
        }
    }

}