dubbo为consumer创建代理

ReferenceConfig.init()方法中获取到了最终的代理对象，先观察一下代理对象的视图。

默认使用javassist生成动态类，可配置proxy为jdk，则使用jdk动态代理：

<dubbo:reference id="hello" interface="com.zhang.HelloService" proxy="jdk" merger="true" check="false"/>

jdk代理对象视图如下图：

RegistryDirectory中有一个 urlInvokerMap。

// Map<url, Invoker> cache service url to invoker mapping.
private volatile Map<String, Invoker<T>> urlInvokerMap;

示例：

键: dubbo://192.168.233.6:20880/com.zhang.HelloService?anyhost=true&application=consumerk_app&check=false&dubbo=2.5.2&group=a&interface=com.zhang.HelloService&iothreads=2&merger=true&methods=sayHello,sayException,sayHi,sayFuck&pid=6736&sayException.retries=0&sayFuck.retries=0&sayFuck.return=true&sayHello.retries=0&sayHi.retries=0&side=consumer&timeout=6000&timestamp=1516256748120
值: com.alibaba.dubbo.registry.integration.RegistryDirectory$InvokerDelegete@4147e2b6

然后分析代理的创建过程，主要的调用栈如下：

贴出Protocol$Adpative的代码：

package com.alibaba.dubbo.rpc;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class Protocol$Adpative implements com.alibaba.dubbo.rpc.Protocol {
    public void destroy() {
        throw new UnsupportedOperationException(
                "method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
    }

    public int getDefaultPort() {
        throw new UnsupportedOperationException(
                "method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
    }

    public com.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0,
            com.alibaba.dubbo.common.URL arg1) throws java.lang.Class {
        if (arg1 == null)
            throw new IllegalArgumentException("url == null");
        com.alibaba.dubbo.common.URL url = arg1;
        //url不同，获得的扩展名是不一样的
        String extName = (url.getProtocol() == null ? "dubbo" : url
                .getProtocol());
        if (extName == null)
            throw new IllegalStateException(
                    "Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
                            + url.toString() + ") use keys([protocol])");
        com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
                .getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class)
                .getExtension(extName);
        return extension.refer(arg0, arg1);
    }

    public com.alibaba.dubbo.rpc.Exporter export(
            com.alibaba.dubbo.rpc.Invoker arg0)
            throws com.alibaba.dubbo.rpc.Invoker {
        if (arg0 == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.Invoker argument == null");
        if (arg0.getUrl() == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.Invoker argument getUrl() == null");
        com.alibaba.dubbo.common.URL url = arg0.getUrl();
        String extName = (url.getProtocol() == null ? "dubbo" : url
                .getProtocol());
        if (extName == null)
            throw new IllegalStateException(
                    "Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
                            + url.toString() + ") use keys([protocol])");
        com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
                .getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class)
                .getExtension(extName);
        return extension.export(arg0);
    }
}

从调用栈可以看到，Protocol$Adpative.refer(Class, URL)调用了2次。但是传递的URL参数是不一样的，

第一次获取的protocol是 ProtocolFilterWrapper/ProtocolListenerWrapper/RegistryProtocol，
第二次获取的protocol是 ProtocolFilterWrapper/ProtocolListenerWrapper/DubboProtocol。

所以在ProtocolListenerWrapper和ProtocolFilterWrapper中走的分支不同。
（第一次的URL是：
registry://192.168.153.1:2181/com.alibaba.dubbo.registry.RegistryService?application=consumer&dubbo=2.1.2&localhost=true&pid=2504&refer=application%3Dconsumer%26dubbo%3D2.1.2%26interface%3Dcom.zhang.HelloService%26methods%3DsayHello%26pid%3D2504%26timestamp%3D1516461886484&registry=zookeeper&timestamp=1516461886531
Protocol$Adpative.refer的refer方法中，getExtension()返回的扩展是ProtocolListenerWrapper/ProtocolFilterWrapper/RegistryProtocol。
第二次的URL是：
dubbo://192.168.153.1:20880/com.zhang.HelloService?anyhost=true&application=consumer&check=false&dubbo=2.1.2&interface=com.zhang.HelloService&methods=sayHello&pid=2504&timestamp=1516461886484）

//ProtocolListenerWrapper类
public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
    if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
        //先进这个分支
        return protocol.refer(type, url);
    }
    //后续再进这个分支
    return new ListenerInvokerWrapper<T>(protocol.refer(type, url), 
            Collections.unmodifiableList(
                    ExtensionLoader.getExtensionLoader(InvokerListener.class)
                    .getActivateExtension(url, Constants.INVOKER_LISTENER_KEY)));
}

//ProtocolFilterWrapper类
public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
    if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
        //先进这个分支
        return protocol.refer(type, url);
    }
    //后续再进这个分支
    return buildInvokerChain(protocol.refer(type, url), Constants.REFERENCE_FILTER_KEY, Constants.CONSUMER);
}

ReferenceConfig<T>的createProxy方法负责创建代理，分析之后得到的步骤大致如下：

1. 生成invoker

// ReferenceConfig.createProxy方法。refprotocol是Protocol$Adpative对象
invoker = refprotocol.refer(interfaceClass, url);

    1.1 生成filter链（使用内部类把filter和next封装起来。相当于创建一个类，有Filter属性，和Invoker属性）

//ProtocolFilterWrapper类
private static <T> Invoker<T> buildInvokerChain(final Invoker<T> invoker, String key, String group) {
    Invoker<T> last = invoker;
    // ConsumerContextFilter, MonitorFilter, FutureFilter
    List<Filter> filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);
    if (filters.size() > 0) {
        for (int i = filters.size() - 1; i >= 0; i --) {
            final Filter filter = filters.get(i);
            final Invoker<T> next = last;
            last = new Invoker<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 filter.invoke(next, invocation);
                }
                public void destroy() {
                    invoker.destroy();
                }
                @Override
                public String toString() {
                    return invoker.toString();
                }
            };
        }
    }
    return last;
}

    1.2 生成RegistryDirectory$InvokerDelegete对象

// RegistryDirectory.toInvokers
// protocol.refer(serviceType, url)就是调用Protocol$Adpative的refer方法，即递归调用
invoker = new InvokerDelegete<T>(protocol.refer(serviceType, url), url, providerUrl);

    1.3 生成MockClusterInvoker。涉及2个类：Protocol$Adpative和Cluster$Adpative，调用栈如下，

package com.alibaba.dubbo.rpc.cluster;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class Cluster$Adpative implements com.alibaba.dubbo.rpc.cluster.Cluster {
    public com.alibaba.dubbo.rpc.Invoker join(
            com.alibaba.dubbo.rpc.cluster.Directory arg0)
            throws com.alibaba.dubbo.rpc.cluster.Directory {
        if (arg0 == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.cluster.Directory argument == null");
        if (arg0.getUrl() == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.cluster.Directory argument getUrl() == null");
        com.alibaba.dubbo.common.URL url = arg0.getUrl();
        String extName = url.getParameter("cluster", "failover");
        if (extName == null)
            throw new IllegalStateException(
                    "Fail to get extension(com.alibaba.dubbo.rpc.cluster.Cluster) name from url("
                            + url.toString() + ") use keys([cluster])");
        com.alibaba.dubbo.rpc.cluster.Cluster extension = (com.alibaba.dubbo.rpc.cluster.Cluster) ExtensionLoader
                .getExtensionLoader(com.alibaba.dubbo.rpc.cluster.Cluster.class)
                .getExtension(extName);
        // extension是MockClusterWrapper
        return extension.join(arg0);
    }
}

2. 创建代理。

private static final ProxyFactory proxyFactory = 
        ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();
private T createProxy(Map<String, String> map) {
    // 省略其他代码
    return (T) proxyFactory.getProxy(invoker);
}

/META-INF/dubbo/internal/com.alibaba.dubbo.rpc.ProxyFactory文件内容：

stub=com.alibaba.dubbo.rpc.proxy.wrapper.StubProxyFactoryWrapper
jdk=com.alibaba.dubbo.rpc.proxy.jdk.JdkProxyFactory
javassist=com.alibaba.dubbo.rpc.proxy.javassist.JavassistProxyFactory

可以看到上面有一个wrapper，所以调用getExtension方法获得的扩展是StubProxyFactoryWrapper。

动态生成的ProxyFactory$Adpative类代码，格式化如下：

package com.alibaba.dubbo.rpc;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class ProxyFactory$Adpative implements com.alibaba.dubbo.rpc.ProxyFactory {
    public java.lang.Object getProxy(com.alibaba.dubbo.rpc.Invoker arg0)
            throws com.alibaba.dubbo.rpc.Invoker {
        if (arg0 == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.Invoker argument == null");
        if (arg0.getUrl() == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.Invoker argument getUrl() == null");
        com.alibaba.dubbo.common.URL url = arg0.getUrl();
        String extName = url.getParameter("proxy", "javassist");
        if (extName == null)
            throw new IllegalStateException(
                    "Fail to get extension(com.alibaba.dubbo.rpc.ProxyFactory) name from url("
                            + url.toString() + ") use keys([proxy])");
        com.alibaba.dubbo.rpc.ProxyFactory extension = (com.alibaba.dubbo.rpc.ProxyFactory) ExtensionLoader
                .getExtensionLoader(com.alibaba.dubbo.rpc.ProxyFactory.class)
                .getExtension(extName);
        // extension其实是StubProxyFactoryWrapper对象，对JavassistProxyFactory做一个wrap
        return extension.getProxy(arg0);
    }

    public com.alibaba.dubbo.rpc.Invoker getInvoker(java.lang.Object arg0,
            java.lang.Class arg1, com.alibaba.dubbo.common.URL arg2)
            throws java.lang.Object {
        if (arg2 == null)
            throw new IllegalArgumentException("url == null");
        com.alibaba.dubbo.common.URL url = arg2;
        String extName = url.getParameter("proxy", "javassist");
        if (extName == null)
            throw new IllegalStateException(
                    "Fail to get extension(com.alibaba.dubbo.rpc.ProxyFactory) name from url("
                            + url.toString() + ") use keys([proxy])");
        com.alibaba.dubbo.rpc.ProxyFactory extension = (com.alibaba.dubbo.rpc.ProxyFactory) ExtensionLoader
                .getExtensionLoader(com.alibaba.dubbo.rpc.ProxyFactory.class)
                .getExtension(extName);
        return extension.getInvoker(arg0, arg1, arg2);
    }
}

 所以getExtension的返回对象是：StubProxyFactoryWrapper/JavassistProxyFactory

// JavassistProxyFactory
public <T> T getProxy(Invoker<T> invoker, Class<?>[] interfaces) {
    //一、 Proxy p = Proxy.getProxy(interfaces);
    //二、 p.newInstance(new InvokerInvocationHandler(invoker));
    return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
}

Proxy0和proxy0是javassist动态生成的类：其中p是Proxy0实例，调用newInstance(InvocationHandler)方法创建proxy0实例。

下面是推测的代码（大概）：

class com.alibaba.dubbo.common.bytecode.Proxy0 extends com.alibaba.dubbo.common.bytecode.Proxy {
    public Object newInstance(java.lang.reflect.InvocationHandler h){
        return new com.alibaba.dubbo.common.bytecode.proxy0($1);
    }
}

class com.alibaba.dubbo.common.bytecode.proxy0 implements
    com.alibaba.dubbo.rpc.service.EchoService, com.zhang.HelloService {
    public <init>(java.lang.reflect.InvocationHandler arg0){
        handler=$1;
    }
    public static java.lang.reflect.Method[] methods;
    private java.lang.reflect.InvocationHandler handler;
    
    public java.lang.String sayHello(){
        Object[] args = new Object[0];
        Object ret = handler.invoke(this, methods[0], args);
        return (java.lang.String)ret;
    }
    public java.lang.Object $echo(java.lang.Object arg0){
        Object[] args = new Object[1];
        args[0] = ($w)$1;
        Object ret = handler.invoke(this, methods[1], args);
        return (java.lang.Object)ret;
    }
}