Dubbo服务服务暴露之ProxyFactory Invoker

Dubbo服务暴露过程中有涉及到调用ProxyFactory 中方法获取Invoker对象的过程，现在我们来深究下源码，来看下这个过程是在做些什么，返回的Invoker 对象是什么，我们来看一下代码的切入点：

Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url);

这里proxyFactory实在ServiceConfig中定义的静态常量，赋值后无法修改：

private static final ProxyFactory proxyFactory = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();

proxyFactory通过ExtensionLoader拓展机制进行加载。查看ProxyFactory接口源码如下：

/*
* Copyright 1999-2011 Alibaba Group.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*
http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.alibaba.dubbo.rpc;
import com.alibaba.dubbo.common.Constants;
import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.common.extension.Adaptive;
import com.alibaba.dubbo.common.extension.SPI;
/**
* ProxyFactory. (API/SPI, Singleton, ThreadSafe)
*
* @author william.liangf
*/
@SPI("javassist")
public interface ProxyFactory {
/**
* create proxy.
*
* @param invoker
* @return proxy
*/
@Adaptive({Constants.PROXY_KEY})
<T> T getProxy(Invoker<T> invoker) throws RpcException;
/**
* create invoker.
*
* @param <T>
* @param proxy
* @param type
* @param url
* @return invoker
*/
@Adaptive({Constants.PROXY_KEY})
<T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) throws RpcException;
}

ProxyFactory接口有三个实现类，分别为JavassistProxyFactory、JdkProxyFactory、StubProxyFactoryWrapper。其中JavassistProxyFactory、JdkProxyFactory作为代理工厂，StubProxyFactoryWrapper实现了对代理工厂进行装饰的功能。在Dubbo中通过SPI配置默认的代理工厂为JavassistProxyFactory

接下来我们重点来看JavassistProxyFactory 代理工厂：

继承图如下：

JavassistProxyFactory 源码非常简单，只有两个方法：(代码调试的入参已经注释在源码中)

/*
* Copyright 1999-2011 Alibaba Group.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*
http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.alibaba.dubbo.rpc.proxy.javassist;
import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.common.bytecode.Proxy;
import com.alibaba.dubbo.common.bytecode.Wrapper;
import com.alibaba.dubbo.rpc.Invoker;
import com.alibaba.dubbo.rpc.proxy.AbstractProxyFactory;
import com.alibaba.dubbo.rpc.proxy.AbstractProxyInvoker;
import com.alibaba.dubbo.rpc.proxy.InvokerInvocationHandler;
/**
* JavaassistRpcProxyFactory
*
* @author william.liangf
*/
public class JavassistProxyFactory extends AbstractProxyFactory {
@SuppressWarnings("unchecked")
public <T> T getProxy(Invoker<T> invoker, Class<?>[] interfaces) {
return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
}
/**
*
* @param proxy DemoServiceImpl
* @param type interface com.alibaba.dubbo.demo.DemoService
* @param url
injvm://127.0.0.1/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&default.accepts=1000&default.threadpool=fixed&default.threads=100&default.timeout=5000&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&methods=sayHello&owner=uce&pid=9176&side=provider&timestamp=1527927801444
* @param <T>
* @return
*/
public <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) {
// TODO Wrapper类不能正确处理带$的类名
final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf('$') < 0 ? proxy.getClass() : type);
return new AbstractProxyInvoker<T>(proxy, type, url) {
@Override
protected Object doInvoke(T proxy, String methodName,
Class<?>[] parameterTypes,
Object[] arguments) throws Throwable {
return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments);
}
};
}
}

其中getProxy是实现抽象类AbstractProxyFactory中的抽象方法。AbstractProxyFactory抽象类实现了ProxyFactory接口中getProxy方法，JdkProxyFactory也实现了抽象类AbstractProxyFactory中的getProxy抽象方法。Javassist与Jdk动态代理的共同部分被封装在父类AbstractProxyFactory中，具体的实现类只需负责实现代理生成过程的差异化部分。

其中getInvoker方法是在ProxyFactory接口中定义的，用于创建Invoker。getInvoker中代码很简单，直接返回一个匿名类。匿名类继承了AbstractProxyInvoker抽象类，AbstractProxyInvoker抽象类又实现了Invoker接口，即表明该匿名类实现了Invoker接口，匿名类是封装了服务提供者的调用者。

Invoker接口定义了一个泛型。定义的方法很简单，只有两个方法，如下：

package com.alibaba.dubbo.rpc;
import com.alibaba.dubbo.common.Node;
public interface Invoker<T> extends Node {
//获取服务对象接口
Class<T> getInterface();
//获取封装了服务的调用者
Result invoke(Invocation invocation) throws RpcException;
}

抽象类AbstractProxyInvoker实现了Invoker接口，AbstractProxyInvoker定义属性和构造方法如下：

private final T proxy;
private final Class<T> type;
private final URL url;
public AbstractProxyInvoker(T proxy, Class<T> type, URL url) {
if (proxy == null) {
throw new IllegalArgumentException("proxy == null");
}
if (type == null) {
throw new IllegalArgumentException("interface == null");
}
if (!type.isInstance(proxy)) {
throw new IllegalArgumentException(proxy.getClass().getName() + " not implement interface " + type);
}
this.proxy = proxy;
this.type = type;
this.url = url;
}

• proxy：是final类型变量，指向服务提供者
• type：是final类型变量，服务的接口类型
• url：是final类型变量，携带服务地址、端口等多种信息的自定义URL对象

AbstractProxyInvoker也实现了invoker方法。方法内部很简单，直接通过RpcResult创建一个对象即可，创建RpcResult时的构建参数是通过方法doInvoke生成的。如下：

public Result invoke(Invocation invocation) throws RpcException {
try {
return new RpcResult(doInvoke(proxy, invocation.getMethodName(), invocation.getParameterTypes(), invocation.getArguments()));
} catch (InvocationTargetException e) {
return new RpcResult(e.getTargetException());
} catch (Throwable e) {
throw new RpcException("Failed to invoke remote proxy method " + invocation.getMethodName() + " to " + getUrl() + ", cause: " + e.getMessage(), e);
}
}

这里的doInvoke方法是抽象方法，由子类实现。抽象方法定义如下：

protected abstract Object doInvoke(T proxy, String methodName, Class<?>[] parameterTypes, Object[] arguments) throws Throwable;

在ProxyFactory接口JavassistProxyFactory实现类中，getInvoker方法内部通过匿名内部类实现了doInvoke抽象方法。

Result接口主要定义了RPC 调用的相关方法，如下：

package com.alibaba.dubbo.rpc;
import java.util.Map;
public interface Result {
Object getValue();
Throwable getException();
boolean hasException();
Object recreate() throws Throwable;
@Deprecated
Object getResult();
Map<String, String> getAttachments();
String getAttachment(String key);
String getAttachment(String key, String defaultValue);
}

RpcResult是对Result接口的一个实现。可看作对传入对象Object的一个包装，部分源码如下：

public class RpcResult implements Result, Serializable {
private static final long serialVersionUID = -6925924956850004727L;
private Object result;
private Throwable exception;
private Map<String, String> attachments = new HashMap<String, String>();
public RpcResult() {
}
public RpcResult(Object result) {
this.result = result;
}
public RpcResult(Throwable exception) {
this.exception = exception;
}
public Object recreate() throws Throwable {
if (exception != null) {
throw exception;
}
return result;
}
}

这就是Dubbo服务发布的Invoker生成过程