分布式系统的跟踪系统Dubbo RPC处理

   接着前一篇博文http://blog.csdn.net/doctor_who2004/article/details/46974695      

    上篇只是提供了一个思想，今天具体给出dubbo rpc 处理细节。

   dubbo prc处理部分，那就是dubbo 的filter 扩展。dubbo 的filter 接口：

/* * 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.extension.SPI;/** * Filter. (SPI, Singleton, ThreadSafe) *  * @author william.liangf */@SPIpublic interface Filter {/** * do invoke filter. *  * <code> * // before filter     * Result result = invoker.invoke(invocation);     * // after filter     * return result;     * </code>     *      * @see com.alibaba.dubbo.rpc.Invoker#invoke(Invocation) * @param invoker service * @param invocation invocation. * @return invoke result. * @throws RpcException */Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException;}

因为，这个过滤器里面只有一个方法，所以，我们如何在prc通信中，传递我们需要的东西呢，那就是看这个方法了。

可以参看dubbo 官方文档，我们要看的就是com.alibaba.dubbo.rpc.Invocation:

/* * 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();}

我们看一下这个接口的实现类：com.alibaba.dubbo.rpc.RpcInvocation:

这个类里面有几个方法：setAttachment、getAttachment等，是我们自定义传递RPC参数的地方。

所以，利用好这几个方法，我们就可以在Dubbo prc 网络通信中，传递我们需要传递的信息，当然，在本文中，指的是跟踪用的对象结构（能把调用链还原成树形结构的数据结构）。

当然，我们可以利用filter保存或打印出一些信息，比如方法名、传递参数名、prc返回结果及异常信息：例如

log.info("[{}] , [{}], [{}], {}, [{}], [{}], [{}ms]   ", uuid, invoker.getInterface(), invocation.getMethodName(), Arrays.toString(invocation.getArguments()), result.getValue(), result.getException(), elapsed);

具体实现就不贴代码了。