dubbo集群容错与负载均衡源码解读

https://dubbo.gitbooks.io/dubbo-user-book/preface/architacture.html

首先连接一下概念

整个Dubbo的RPC框架建立在Protocol、Exporter和Invoker这三个接口上，Protocol扩展点定义了一种RPC协议的实现，即如何发布和引用服务，Exporter代表了一个对外暴露的服务，Invoker执行远程调用并返回结果，实现一个协议要同时实现这三个接口。下面先看一下这三个接口，稍微有点抽象。

1. Protocol

Protocol的源码如下，代码的注释已讲的比较清楚，这里可以看到，Dubbo默认使用的协议是dubbo。

 折叠原码

/*  * 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.URL; import com.alibaba.dubbo.common.extension.Adaptive; import com.alibaba.dubbo.common.extension.SPI;   /**  * Protocol. (API/SPI, Singleton, ThreadSafe)  *  * @author william.liangf  */ @SPI("dubbo") public interface Protocol {           /**      * 获取缺省端口，当用户没有配置端口时使用。      *      * @return 缺省端口      */     int getDefaultPort();       /**      * 暴露远程服务：<br>      * 1. 协议在接收请求时，应记录请求来源方地址信息：RpcContext.getContext().setRemoteAddress();<br>      * 2. export()必须是幂等的，也就是暴露同一个URL的Invoker两次，和暴露一次没有区别。<br>      * 3. export()传入的Invoker由框架实现并传入，协议不需要关心。<br>      *      * @param <T> 服务的类型      * @param invoker 服务的执行体      * @return exporter 暴露服务的引用，用于取消暴露      * @throws RpcException 当暴露服务出错时抛出，比如端口已占用      */     @Adaptive     <T> Exporter<T> export(Invoker<T> invoker) throws RpcException;       /**      * 引用远程服务：<br>      * 1. 当用户调用refer()所返回的Invoker对象的invoke()方法时，协议需相应执行同URL远端export()传入的Invoker对象的invoke()方法。<br>      * 2. refer()返回的Invoker由协议实现，协议通常需要在此Invoker中发送远程请求。<br>      * 3. 当url中有设置check=false时，连接失败不能抛出异常，并内部自动恢复。<br>      *      * @param <T> 服务的类型      * @param type 服务的类型      * @param url 远程服务的URL地址      * @return invoker 服务的本地代理      * @throws RpcException 当连接服务提供方失败时抛出      */     @Adaptive     <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException;       /**      * 释放协议：<br>      * 1. 取消该协议所有已经暴露和引用的服务。<br>      * 2. 释放协议所占用的所有资源，比如连接和端口。<br>      * 3. 协议在释放后，依然能暴露和引用新的服务。<br>      */     void destroy();   }

 

2. Exporter

Exporter代表了一个对外暴露的服务，其源码如下，getInvoker返回调用服务的Invoker，unexport取消该服务的暴露。

 折叠原码

/*  * 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;   /**  * Exporter. (API/SPI, Prototype, ThreadSafe)  *  * @see com.alibaba.dubbo.rpc.Protocol#export(Invoker)  * @see com.alibaba.dubbo.rpc.ExporterListener  * @see com.alibaba.dubbo.rpc.protocol.AbstractExporter  * @author william.liangf  */ public interface Exporter<T> {           /**      * get invoker.      *      * @return invoker      */     Invoker<T> getInvoker();           /**      * unexport.      *      * <code>      *     getInvoker().destroy();      * </code>      */     void unexport();   }

 

3. Invoker

Invoker用于执行一个RPC调用，其代码如下，getInterface返回它是哪个服务的Invoker，invoker方法用于执行远程调用，并返回执行结果。

 折叠原码

/*  * 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.Node;   /**  * Invoker. (API/SPI, Prototype, ThreadSafe)  *  * @see com.alibaba.dubbo.rpc.Protocol#refer(Class, com.alibaba.dubbo.common.URL)  * @see com.alibaba.dubbo.rpc.InvokerListener  * @see com.alibaba.dubbo.rpc.protocol.AbstractInvoker  * @author william.liangf  */ public interface Invoker<T> extends Node {       /**      * get service interface.      *      * @return service interface.      */     Class<T> getInterface();       /**      * invoke.      *      * @param invocation      * @return result      * @throws RpcException      */     Result invoke(Invocation invocation) throws RpcException;   }

 

 

Invoker接口扩展自Node接口，Node代表了一个具有URL地址的节点，其源码如下，getUrl返回该节点的URL地址，isAvailable返回该节点当前是否可用，destory用于销毁该节点。

 折叠原码

/*  * 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.common;   import com.alibaba.dubbo.common.URL;   /**  * Node. (API/SPI, Prototype, ThreadSafe)  *  * @author william.liangf  */ public interface Node {       /**      * get url.      *      * @return url.      */     URL getUrl();           /**      * is available.      *      * @return available.      */     boolean isAvailable();       /**      * destroy.      */     void destroy();   }

 

下面看一下Result接口，Result接口代表了RPC调用的执行结果，其源码如下，getValue返回执行结果的值，如果没有执行结果则返回null，getException返回执行过程中发生的异常，如果没有发生异常，则返回null，hasException用于返回是否发生了异常，recreate方法用于重建执行结果，重建的意思就是，模拟执行，然后获取结果，如果执行正常，则返回值，否则抛出异常。三个attachment用于获取执行中的其他附加信息。

 折叠原码

/*  * 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 java.util.Map;   /**  * RPC invoke result. (API, Prototype, NonThreadSafe)  *  * @serial Don't change the class name and package name.  * @see com.alibaba.dubbo.rpc.Invoker#invoke(Invocation)  * @see com.alibaba.dubbo.rpc.RpcResult  * @author qianlei  * @author william.liangf  */ public interface Result {      /**     * Get invoke result.     *     * @return result. if no result return null.     */    Object getValue();      /**     * Get exception.     *     * @return exception. if no exception return null.     */    Throwable getException();       /**      * Has exception.      *      * @return has exception.      */     boolean hasException();       /**      * Recreate.      *      * <code>      * if (hasException()) {      *     throw getException();      * } else {      *     return getValue();      * }      * </code>      *      * @return result.      * @throws if has exception throw it.      */     Object recreate() throws Throwable;       /**      * @deprecated Replace to getValue()      * @see com.alibaba.dubbo.rpc.Result#getValue()      */     @Deprecated     Object getResult();         /**      * get attachments.      *      * @return attachments.      */     Map<String, String> getAttachments();       /**      * get attachment by key.      *      * @return attachment value.      */     String getAttachment(String key);       /**      * get attachment by key with default value.      *      * @return attachment value.      */     String getAttachment(String key, String defaultValue);   }

 

Invocation表示执行的上下文，其源码如下，getMethodName返回调用的是哪个方法，getParameterTypes返回所要调用的方法的参数类，getArguments返回调用方法时使用的参数，三个attachment方法同样是用于获取一些附加信息，getInvoker返回当前上下文是属于哪个Invoker。

 折叠原码

/*  * 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 java.util.Map;   /**  * Invocation. (API, Prototype, NonThreadSafe)  *  * @serial Don't change the class name and package name.  * @see com.alibaba.dubbo.rpc.Invoker#invoke(Invocation)  * @see com.alibaba.dubbo.rpc.RpcInvocation  * @author qian.lei  * @author william.liangf  */ public interface Invocation {      /**     * get method name.     *     * @serial     * @return method name.     */    String getMethodName();      /**     * get parameter types.     *     * @serial     * @return parameter types.     */    Class<?>[] getParameterTypes();      /**     * get arguments.     *     * @serial     * @return arguments.     */    Object[] getArguments();      /**     * get attachments.     *     * @serial     * @return attachments.     */    Map<String, String> getAttachments();         /**      * get attachment by key.      *      * @serial      * @return attachment value.      */    String getAttachment(String key);         /**      * get attachment by key with default value.      *      * @serial      * @return attachment value.      */    String getAttachment(String key, String defaultValue);       /**      * get the invoker in current context.      *      * @transient      * @return invoker.      */     Invoker<?> getInvoker();   }

URL

http://www.hiwzc.com/dubbo-url.html

http://youaremoon.iteye.com/blog/2279787

 

调用关系

http://blog.youkuaiyun.com/quhongwei_zhanqiu/article/details/41701689