Dubbo服务服务暴露之ProxyFactory Invoker-白红宇

Dubbo服务服务暴露之ProxyFactory Invoker

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发布时间：2019-06-21

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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 getProxy(Invoker
     
       invoker) throws RpcException;    /**     * create invoker.     *     * @param 
      
            * @param proxy     * @param type     * @param url     * @return invoker     */    @Adaptive({Constants.PROXY_KEY})    
       
         Invoker
        
          getInvoker(T proxy, Class
         
           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 getProxy(Invoker
     
       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 
      
            * @return     */    public 
       
         Invoker
        
          getInvoker(T proxy, Class
         
           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
          
           (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
    
      extends Node {   //获取服务对象接口    Class
     
       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
    
      type;    private final URL url;    public AbstractProxyInvoker(T proxy, Class
     
       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
    
      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
    
      attachments = new HashMap
     
      ();    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

转载于:https://my.oschina.net/LucasZhu/blog/1833087

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