内容简介：在现行微服务的趋势下，一次调用的过程中涉及多个服务节点，产生的日志分布在不同的服务器上，虽说可以使用ELK技术将分散的日志，汇总到es中，但是如何将这些日志贯穿起来，则是一个关键问题。如果需要查看一次调用的全链路日志，则一般的做法是通过在系统边界中产生一个在使用HTTP协议作为服务协议的系统里，可以统一使用一个封装好的http client做traceId透传。但是dubbo实现traceId透传就稍微复杂些了。根据上节讲的
在现行微服务的趋势下，一次调用的过程中涉及多个服务节点，产生的日志分布在不同的服务器上，虽说可以使用ELK技术将分散的日志，汇总到es中，但是如何将这些日志贯穿起来，则是一个关键问题。
如果需要查看一次调用的全链路日志，则一般的做法是通过在系统边界中产生一个 traceId ，向调用链的后续服务传递 traceId ，后续服务继续使用 traceId 打印日志，并再向其他后续服务传递 traceId ，此过程简称， traceId透传 。
在使用HTTP协议作为服务协议的系统里，可以统一使用一个封装好的http client做traceId透传。但是dubbo实现traceId透传就稍微复杂些了。根据上节讲的 《☆聊聊Dubbo（六）：核心源码-Filter链原理》 ，一般情况下， 会自定义Filter来实现traceId透传 ，但还有两种比较特殊的实现方式： （1）重新实现dubbo内部的相关类；（2）基于RpcContext实现；
1 基于重写实现
1.1 源码分析
Proxy是 Dubbo 使用javassist为consumer 端service生成的动态代理instance。
Implement是provider端的service实现instance。
traceId透传，即要求Proxy 和 Implement具有相同的traceId。Dubbo具有良好的分层特征， transport的对象是RPCInvocation 。
所以，重写的重点逻辑实现，就是Proxy将traceId放入RPCInvocation，交由Client进行序列化和TCP传输，Server反序列化得到RPCInvocation，取出traceId，交由Implement即可。
下面为consumer端 JavassistProxyFactory 的代码分析：
public class JavassistProxyFactory extends AbstractProxyFactory {
/**
* Spring容器启动时，该代理工厂类方法会为Consumer生成Service代理类
* invoker和interfaces都是从Spring配置文件中读取出来
*/
@SuppressWarnings("unchecked")
public <T> T getProxy(Invoker<T> invoker, Class<?>[] interfaces) {
// 生成Service代理类的每个方法的字节码，都调用了InvokerInvocationHandler.invoke(...)方法，
// 做实际RpcInvocation包装、序列化、TCP传输、反序列化结果
return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
}
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);
}
};
}
}
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下面为consumer端 InvokerInvocationHandler 的代码分析：
public class InvokerInvocationHandler implements InvocationHandler {
private final Invoker<?> invoker;
public InvokerInvocationHandler(Invoker<?> handler){
this.invoker = handler;
}
/**
* 真正调用RPC时，各个Service代理的字节码里调用了这个通用的invoke
* proxy就是之前生成的代理对象，第二个参数是方法名，第三个参数是参数列表
* 知道了（1）哪个接口（2）哪个方法（3）参数是什么，就完全可以映射到Provider端实现并获取返回值
*/
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
Class<?>[] parameterTypes = method.getParameterTypes();
if (method.getDeclaringClass() == Object.class) {
return method.invoke(invoker, args);
}
if ("toString".equals(methodName) && parameterTypes.length == 0) {
return invoker.toString();
}
if ("hashCode".equals(methodName) && parameterTypes.length == 0) {
return invoker.hashCode();
}
if ("equals".equals(methodName) && parameterTypes.length == 1) {
return invoker.equals(args[0]);
}
// 因为到这里，还是consumer端的业务线程，所以在这里取ThreadLocal里的traceId，
// 再放入RpcInvocation的attachment，那么Provider就可以从收到的RpcInvocation实例取出透传的traceId
return invoker.invoke(new RpcInvocation(method, args)).recreate();
}
}
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下面为Provider端 DubboProtocol 的代码分析：
private ExchangeHandler requestHandler = new ExchangeHandlerAdapter() {
public Object reply(ExchangeChannel channel, Object message) throws RemotingException {
if (message instanceof Invocation) {
Invocation inv = (Invocation) message;
Invoker<?> invoker = getInvoker(channel, inv);
//如果是callback 需要处理高版本调用低版本的问题
if (Boolean.TRUE.toString().equals(inv.getAttachments().get(IS_CALLBACK_SERVICE_INVOKE))){
String methodsStr = invoker.getUrl().getParameters().get("methods");
boolean hasMethod = false;
if (methodsStr == null || methodsStr.indexOf(",") == -1){
hasMethod = inv.getMethodName().equals(methodsStr);
} else {
String[] methods = methodsStr.split(",");
for (String method : methods){
if (inv.getMethodName().equals(method)){
hasMethod = true;
break;
}
}
}
if (!hasMethod){
logger.warn(new IllegalStateException("The methodName "+inv.getMethodName()+" not found in callback service interface ,invoke will be ignored. please update the api interface. url is:" + invoker.getUrl()) +" ,invocation is :"+inv );
return null;
}
}
// Provider收到报文之后，从线程池中取出一个线程，反序列化出RpcInvocation、并调用实现类的对应方法
// 所以，此处就是Provider端的实现类的线程，取出traceId，放入ThreadLocal中
RpcContext.getContext().setRemoteAddress(channel.getRemoteAddress());
return invoker.invoke(inv);
}
throw new RemotingException(channel, "Unsupported request: " + message == null ? null : (message.getClass().getName() + ": " + message) + ", channel: consumer: " + channel.getRemoteAddress() + " --> provider: " + channel.getLocalAddress());
}
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1.2 具体实现
package com.alibaba.dubbo.rpc.proxy;
/**
* traceId工具类这个类是新添加的
*/
public class TraceIdUtil {
private static final ThreadLocal<String> TRACE_ID = new ThreadLocal<String>();
public static String getTraceId() {
return TRACE_ID.get();
}
public static void setTraceId(String traceId) {
TRACE_ID.set(traceId);
}
}
/**
* InvokerHandler 这个类 是修改的
*/
public class InvokerInvocationHandler implements InvocationHandler {
private final Invoker<?> invoker;
public InvokerInvocationHandler(Invoker<?> handler){
this.invoker = handler;
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
Class<?>[] parameterTypes = method.getParameterTypes();
if (method.getDeclaringClass() == Object.class) {
return method.invoke(invoker, args);
}
if ("toString".equals(methodName) && parameterTypes.length == 0) {
return invoker.toString();
}
if ("hashCode".equals(methodName) && parameterTypes.length == 0) {
return invoker.hashCode();
}
if ("equals".equals(methodName) && parameterTypes.length == 1) {
return invoker.equals(args[0]);
}
// 这里将cosumer 端的traceId放入RpcInvocation
RpcInvocation rpcInvocation = new RpcInvocation(method, args);
rpcInvocation.setAttachment("traceId", TraceIdUtil.getTraceId());
return invoker.invoke(rpcInvocation).recreate();
}
}
package com.alibaba.dubbo.rpc.protocol.dubbo;
/**
* dubbo protocol support 重新实现DubboProtocol
*
*/
public class DubboProtocol extends AbstractProtocol {
private ExchangeHandler requestHandler = new ExchangeHandlerAdapter() {
public Object reply(ExchangeChannel channel, Object message) throws RemotingException {
if (message instanceof Invocation) {
Invocation inv = (Invocation) message;
Invoker<?> invoker = getInvoker(channel, inv);
//如果是callback 需要处理高版本调用低版本的问题
if (Boolean.TRUE.toString().equals(inv.getAttachments().get(IS_CALLBACK_SERVICE_INVOKE))){
String methodsStr = invoker.getUrl().getParameters().get("methods");
boolean hasMethod = false;
if (methodsStr == null || methodsStr.indexOf(",") == -1){
hasMethod = inv.getMethodName().equals(methodsStr);
} else {
String[] methods = methodsStr.split(",");
for (String method : methods){
if (inv.getMethodName().equals(method)){
hasMethod = true;
break;
}
}
}
if (!hasMethod){
logger.warn(new IllegalStateException("The methodName "+inv.getMethodName()+" not found in callback service interface ,invoke will be ignored. please update the api interface. url is:" + invoker.getUrl()) +" ,invocation is :"+inv );
return null;
}
}
RpcContext.getContext().setRemoteAddress(channel.getRemoteAddress());
// 这里将收到的consumer端的traceId放入provider端的thread local
TraceIdUtil.setTraceId(inv.getAttachment("traceId"));
return invoker.invoke(inv);
}
throw new RemotingException(channel, "Unsupported request: " + message == null ? null : (message.getClass().getName() + ": " + message) + ", channel: consumer: " + channel.getRemoteAddress() + " --> provider: " + channel.getLocalAddress());
}
}
}
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2 基于RpcContext实现
在具体讲解自定义filter来实现透传traceId的方案前，我们先来研究下RpcContext对象。 其RpcContext本质上是个ThreadLocal对象，其维护了一次rpc交互的上下文信息 。
/*
* 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.net.InetSocketAddress;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import com.alibaba.dubbo.common.Constants;
import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.common.utils.NetUtils;
/**
* Thread local context. (API, ThreadLocal, ThreadSafe)
*
* 注意：RpcContext是一个临时状态记录器，当接收到RPC请求，或发起RPC请求时，RpcContext的状态都会变化。
* 比如：A调B，B再调C，则B机器上，在B调C之前，RpcContext记录的是A调B的信息，在B调C之后，RpcContext记录的是B调C的信息。
*
* @see com.alibaba.dubbo.rpc.filter.ContextFilter
* @author qian.lei
* @author william.liangf
* @export
*/
public class RpcContext {
private static final ThreadLocal<RpcContext> LOCAL = new ThreadLocal<RpcContext>() {
@Override
protected RpcContext initialValue() {
return new RpcContext();
}
};
/**
* get context.
*
* @return context
*/
public static RpcContext getContext() {
return LOCAL.get();
}
/**
* remove context.
*
* @see com.alibaba.dubbo.rpc.filter.ContextFilter
*/
public static void removeContext() {
LOCAL.remove();
}
private Future<?> future;
private List<URL> urls;
private URL url;
private String methodName;
private Class<?>[] parameterTypes;
private Object[] arguments;
private InetSocketAddress localAddress;
private InetSocketAddress remoteAddress;
private final Map<String, String> attachments = new HashMap<String, String>();
private final Map<String, Object> values = new HashMap<String, Object>();
// now we don't use the 'values' map to hold these objects
// we want these objects to be as generic as possible
private Object request;
private Object response;
@Deprecated
private List<Invoker<?>> invokers;
@Deprecated
private Invoker<?> invoker;
@Deprecated
private Invocation invocation;
protected RpcContext() {
}
/**
* Get the request object of the underlying RPC protocol, e.g. HttpServletRequest
*
* @return null if the underlying protocol doesn't provide support for getting request
*/
public Object getRequest() {
return request;
}
/**
* Get the request object of the underlying RPC protocol, e.g. HttpServletRequest
*
* @return null if the underlying protocol doesn't provide support for getting request or the request is not of the specified type
*/
@SuppressWarnings("unchecked")
public <T> T getRequest(Class<T> clazz) {
return (request != null && clazz.isAssignableFrom(request.getClass())) ? (T) request : null;
}
public void setRequest(Object request) {
this.request = request;
}
/**
* Get the response object of the underlying RPC protocol, e.g. HttpServletResponse
*
* @return null if the underlying protocol doesn't provide support for getting response
*/
public Object getResponse() {
return response;
}
/**
* Get the response object of the underlying RPC protocol, e.g. HttpServletResponse
*
* @return null if the underlying protocol doesn't provide support for getting response or the response is not of the specified type
*/
@SuppressWarnings("unchecked")
public <T> T getResponse(Class<T> clazz) {
return (response != null && clazz.isAssignableFrom(response.getClass())) ? (T) response : null;
}
public void setResponse(Object response) {
this.response = response;
}
/**
* is provider side.
*
* @return provider side.
*/
public boolean isProviderSide() {
URL url = getUrl();
if (url == null) {
return false;
}
InetSocketAddress address = getRemoteAddress();
if (address == null) {
return false;
}
String host;
if (address.getAddress() == null) {
host = address.getHostName();
} else {
host = address.getAddress().getHostAddress();
}
return url.getPort() != address.getPort() ||
! NetUtils.filterLocalHost(url.getIp()).equals(NetUtils.filterLocalHost(host));
}
/**
* is consumer side.
*
* @return consumer side.
*/
public boolean isConsumerSide() {
URL url = getUrl();
if (url == null) {
return false;
}
InetSocketAddress address = getRemoteAddress();
if (address == null) {
return false;
}
String host;
if (address.getAddress() == null) {
host = address.getHostName();
} else {
host = address.getAddress().getHostAddress();
}
return url.getPort() == address.getPort() &&
NetUtils.filterLocalHost(url.getIp()).equals(NetUtils.filterLocalHost(host));
}
/**
* get future.
*
* @param <T>
* @return future
*/
@SuppressWarnings("unchecked")
public <T> Future<T> getFuture() {
return (Future<T>) future;
}
/**
* set future.
*
* @param future
*/
public void setFuture(Future<?> future) {
this.future = future;
}
public List<URL> getUrls() {
return urls == null && url != null ? (List<URL>) Arrays.asList(url) : urls;
}
public void setUrls(List<URL> urls) {
this.urls = urls;
}
public URL getUrl() {
return url;
}
public void setUrl(URL url) {
this.url = url;
}
/**
* get method name.
*
* @return method name.
*/
public String getMethodName() {
return methodName;
}
public void setMethodName(String methodName) {
this.methodName = methodName;
}
/**
* get parameter types.
*
* @serial
*/
public Class<?>[] getParameterTypes() {
return parameterTypes;
}
public void setParameterTypes(Class<?>[] parameterTypes) {
this.parameterTypes = parameterTypes;
}
/**
* get arguments.
*
* @return arguments.
*/
public Object[] getArguments() {
return arguments;
}
public void setArguments(Object[] arguments) {
this.arguments = arguments;
}
/**
* set local address.
*
* @param address
* @return context
*/
public RpcContext setLocalAddress(InetSocketAddress address) {
this.localAddress = address;
return this;
}
/**
* set local address.
*
* @param host
* @param port
* @return context
*/
public RpcContext setLocalAddress(String host, int port) {
if (port < 0) {
port = 0;
}
this.localAddress = InetSocketAddress.createUnresolved(host, port);
return this;
}
/**
* get local address.
*
* @return local address
*/
public InetSocketAddress getLocalAddress() {
return localAddress;
}
public String getLocalAddressString() {
return getLocalHost() + ":" + getLocalPort();
}
/**
* get local host name.
*
* @return local host name
*/
public String getLocalHostName() {
String host = localAddress == null ? null : localAddress.getHostName();
if (host == null || host.length() == 0) {
return getLocalHost();
}
return host;
}
/**
* set remote address.
*
* @param address
* @return context
*/
public RpcContext setRemoteAddress(InetSocketAddress address) {
this.remoteAddress = address;
return this;
}
/**
* set remote address.
*
* @param host
* @param port
* @return context
*/
public RpcContext setRemoteAddress(String host, int port) {
if (port < 0) {
port = 0;
}
this.remoteAddress = InetSocketAddress.createUnresolved(host, port);
return this;
}
/**
* get remote address.
*
* @return remote address
*/
public InetSocketAddress getRemoteAddress() {
return remoteAddress;
}
/**
* get remote address string.
*
* @return remote address string.
*/
public String getRemoteAddressString() {
return getRemoteHost() + ":" + getRemotePort();
}
/**
* get remote host name.
*
* @return remote host name
*/
public String getRemoteHostName() {
return remoteAddress == null ? null : remoteAddress.getHostName();
}
/**
* get local host.
*
* @return local host
*/
public String getLocalHost() {
String host = localAddress == null ? null :
localAddress.getAddress() == null ? localAddress.getHostName()
: NetUtils.filterLocalHost(localAddress.getAddress().getHostAddress());
if (host == null || host.length() == 0) {
return NetUtils.getLocalHost();
}
return host;
}
/**
* get local port.
*
* @return port
*/
public int getLocalPort() {
return localAddress == null ? 0 : localAddress.getPort();
}
/**
* get remote host.
*
* @return remote host
*/
public String getRemoteHost() {
return remoteAddress == null ? null :
remoteAddress.getAddress() == null ? remoteAddress.getHostName()
: NetUtils.filterLocalHost(remoteAddress.getAddress().getHostAddress());
}
/**
* get remote port.
*
* @return remote port
*/
public int getRemotePort() {
return remoteAddress == null ? 0 : remoteAddress.getPort();
}
/**
* get attachment.
*
* @param key
* @return attachment
*/
public String getAttachment(String key) {
return attachments.get(key);
}
/**
* set attachment.
*
* @param key
* @param value
* @return context
*/
public RpcContext setAttachment(String key, String value) {
if (value == null) {
attachments.remove(key);
} else {
attachments.put(key, value);
}
return this;
}
/**
* remove attachment.
*
* @param key
* @return context
*/
public RpcContext removeAttachment(String key) {
attachments.remove(key);
return this;
}
/**
* get attachments.
*
* @return attachments
*/
public Map<String, String> getAttachments() {
return attachments;
}
/**
* set attachments
*
* @param attachment
* @return context
*/
public RpcContext setAttachments(Map<String, String> attachment) {
this.attachments.clear();
if (attachment != null && attachment.size() > 0) {
this.attachments.putAll(attachment);
}
return this;
}
public void clearAttachments() {
this.attachments.clear();
}
/**
* get values.
*
* @return values
*/
public Map<String, Object> get() {
return values;
}
/**
* set value.
*
* @param key
* @param value
* @return context
*/
public RpcContext set(String key, Object value) {
if (value == null) {
values.remove(key);
} else {
values.put(key, value);
}
return this;
}
/**
* remove value.
*
* @param key
* @return value
*/
public RpcContext remove(String key) {
values.remove(key);
return this;
}
/**
* get value.
*
* @param key
* @return value
*/
public Object get(String key) {
return values.get(key);
}
public RpcContext setInvokers(List<Invoker<?>> invokers) {
this.invokers = invokers;
if (invokers != null && invokers.size() > 0) {
List<URL> urls = new ArrayList<URL>(invokers.size());
for (Invoker<?> invoker : invokers) {
urls.add(invoker.getUrl());
}
setUrls(urls);
}
return this;
}
public RpcContext setInvoker(Invoker<?> invoker) {
this.invoker = invoker;
if (invoker != null) {
setUrl(invoker.getUrl());
}
return this;
}
public RpcContext setInvocation(Invocation invocation) {
this.invocation = invocation;
if (invocation != null) {
setMethodName(invocation.getMethodName());
setParameterTypes(invocation.getParameterTypes());
setArguments(invocation.getArguments());
}
return this;
}
/**
* @deprecated Replace to isProviderSide()
*/
@Deprecated
public boolean isServerSide() {
return isProviderSide();
}
/**
* @deprecated Replace to isConsumerSide()
*/
@Deprecated
public boolean isClientSide() {
return isConsumerSide();
}
/**
* @deprecated Replace to getUrls()
*/
@Deprecated
@SuppressWarnings({ "unchecked", "rawtypes" })
public List<Invoker<?>> getInvokers() {
return invokers == null && invoker != null ? (List)Arrays.asList(invoker) : invokers;
}
/**
* @deprecated Replace to getUrl()
*/
@Deprecated
public Invoker<?> getInvoker() {
return invoker;
}
/**
* @deprecated Replace to getMethodName(), getParameterTypes(), getArguments()
*/
@Deprecated
public Invocation getInvocation() {
return invocation;
}
/**
* 异步调用 ，需要返回值，即使步调用Future.get方法，也会处理调用超时问题.
* @param callable
* @return 通过future.get()获取返回结果.
*/
@SuppressWarnings("unchecked")
public <T> Future<T> asyncCall(Callable<T> callable) {
try {
try {
setAttachment(Constants.ASYNC_KEY, Boolean.TRUE.toString());
final T o = callable.call();
//local调用会直接返回结果.
if (o != null) {
FutureTask<T> f = new FutureTask<T>(new Callable<T>() {
public T call() throws Exception {
return o;
}
});
f.run();
return f;
} else {
}
} catch (Exception e) {
throw new RpcException(e);
} finally {
removeAttachment(Constants.ASYNC_KEY);
}
} catch (final RpcException e) {
return new Future<T>() {
public boolean cancel(boolean mayInterruptIfRunning) {
return false;
}
public boolean isCancelled() {
return false;
}
public boolean isDone() {
return true;
}
public T get() throws InterruptedException, ExecutionException {
throw new ExecutionException(e.getCause());
}
public T get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException,
TimeoutException {
return get();
}
};
}
return ((Future<T>)getContext().getFuture());
}
/**
* oneway调用，只发送请求，不接收返回结果.
* @param callable
*/
public void asyncCall(Runnable runable) {
try {
setAttachment(Constants.RETURN_KEY, Boolean.FALSE.toString());
runable.run();
} catch (Throwable e) {
//FIXME 异常是否应该放在future中？
throw new RpcException("oneway call error ." + e.getMessage(), e);
} finally {
removeAttachment(Constants.RETURN_KEY);
}
}
}
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注：RpcContext里的attachments信息会填入到RpcInvocation对象中, 一起传递过去。
因此有人就建议可以简单的把traceId注入到RpcContext中，这样就可以简单的实现traceId的透传了，事实是否如此，先让我们来一起实践一下。
定义Dubbo接口类：
public interface IEchoService {
String echo(String name);
}
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编写服务端代码（Provider）：
@Service("echoService")
public class EchoServiceImpl implements IEchoService {
@Override
public String echo(String name) {
String traceId = RpcContext.getContext().getAttachment("traceId");
System.out.println("name = " + name + ", traceId = " + traceId);
return name;
}
public static void main(String[] args) {
ClassPathXmlApplicationContext applicationContext =
new ClassPathXmlApplicationContext("spring-dubbo-test-producer.xml");
System.out.println("server start");
while (true) {
try {
Thread.sleep(1000L);
} catch (InterruptedException e) {
}
}
}
}
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编写客户端代码（Consumer）：
public class EchoServiceConsumer {
public static void main(String[] args) {
ClassPathXmlApplicationContext applicationContext =
new ClassPathXmlApplicationContext("spring-dubbo-test-consumer.xml");
IEchoService service = (IEchoService) applicationContext
.getBean("echoService");
// *) 设置traceId
RpcContext.getContext().setAttachment("traceId", "100001");
System.out.println(RpcContext.getContext().getAttachments());
// *) 第一调用
service.echo("lilei");
// *) 第二次调用
System.out.println(RpcContext.getContext().getAttachments());
service.echo("hanmeimei");
}
}
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执行的结果如下：
服务端输出:
name = lilei, traceId = 100001
name = hanmeimei, traceId = null
客户端输出:
{traceId=100001}
{}
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从服务端的输出信息中，我们可以惊喜的发现，traceId确实传递过去了，但是只有第一次有，第二次没有。而从客户端对RpcContext的内容输出，也印证了这个现象，同时产生这个现象的本质原因是 RpcContext对象的attachment在一次rpc交互后被清空了 。
给RpcContext的clearAttachments方法, 设置断点后复现. 我们可以找到如下调用堆栈：
java.lang.Thread.State: RUNNABLE
at com.alibaba.dubbo.rpc.RpcContext.clearAttachments(RpcContext.java:438)
at com.alibaba.dubbo.rpc.filter.ConsumerContextFilter.invoke(ConsumerContextFilter.java:50)
at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:91)
at com.alibaba.dubbo.rpc.protocol.InvokerWrapper.invoke(InvokerWrapper.java:53)
at com.alibaba.dubbo.rpc.cluster.support.FailoverClusterInvoker.doInvoke(FailoverClusterInvoker.java:77)
at com.alibaba.dubbo.rpc.cluster.support.AbstractClusterInvoker.invoke(AbstractClusterInvoker.java:227)
at com.alibaba.dubbo.rpc.cluster.support.wrapper.MockClusterInvoker.invoke(MockClusterInvoker.java:72)
at com.alibaba.dubbo.rpc.proxy.InvokerInvocationHandler.invoke(InvokerInvocationHandler.java:52)
at com.alibaba.dubbo.common.bytecode.proxy0.echo(proxy0.java:-1)
at com.test.dubbo.EchoServiceConsumer.main(EchoServiceConsumer.java:20)
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其最直接的调用为Dubbo自带的ConsumerContextFilter，让我们来分析其代码：
@Activate(
group = {"consumer"},
order = -10000
)
public class ConsumerContextFilter implements Filter {
public ConsumerContextFilter() {
}
public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
RpcContext.getContext().setInvoker(invoker).setInvocation(invocation)
.setLocalAddress(NetUtils.getLocalHost(), 0)
.setRemoteAddress(invoker.getUrl().getHost(), invoker.getUrl().getPort());
if(invocation instanceof RpcInvocation) {
((RpcInvocation)invocation).setInvoker(invoker);
}
Result var3;
try {
var3 = invoker.invoke(invocation);
} finally {
RpcContext.getContext().clearAttachments();
}
return var3;
}
}
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确实在finally代码片段中， 我们发现RpcContext在每次rpc调用后, 都会清空attachment对象 。
既然我们找到了本质原因，那么解决方法， 可以在每次调用的时候，重新设置下traceId ，比如像这样（看着感觉吃像相对难看了一点）：
// *) 第一调用
RpcContext.getContext().setAttachment("traceId", "100001");
service.echo("lilei");
// *) 第二次调用
RpcContext.getContext().setAttachment("traceId", "100001");
service.echo("hanmeimei");
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3 基于Filter实现
先引入一个 工具 类：
package com.test.dubbo;
public class TraceIdFilter implements Filter {
@Override
public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
String traceId = RpcContext.getContext().getAttachment("traceId");
if ( !StringUtils.isEmpty(traceId) ) {
// *) 从RpcContext里获取traceId并保存
TraceIdUtils.setTraceId(traceId);
} else {
// *) 交互前重新设置traceId, 避免信息丢失
RpcContext.getContext().setAttachment("traceId", TraceIdUtils.getTraceId());
}
// *) 实际的rpc调用
return invoker.invoke(invocation);
}
}
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然后我们定义一个Filter类：
package com.test.dubbo;
public class TraceIdFilter implements Filter {
@Override
public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
String traceId = RpcContext.getContext().getAttachment("traceId");
if ( !StringUtils.isEmpty(traceId) ) {
// *) 从RpcContext里获取traceId并保存
TraceIdUtils.setTraceId(traceId);
} else {
// *) 交互前重新设置traceId, 避免信息丢失
RpcContext.getContext().setAttachment("traceId", TraceIdUtils.getTraceId());
}
// *) 实际的rpc调用
return invoker.invoke(invocation);
}
}
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在resource目录下, 添加META-INF/dubbo目录, 继而添加com.alibaba.dubbo.rpc.Filter文件：
编辑（com.alibaba.dubbo.rpc.Filter文件）内容如下：
traceIdFilter=com.test.dubbo.TraceIdFilter 复制代码
然后我们给dubbo的producer和consumer都配置对应的filter项：
服务端:
<dubbo:service interface="com.test.dubbo.IEchoService" ref="echoService" version="1.0.0"
filter="traceIdFilter"/>
客户端:
<dubbo:reference interface="com.test.dubbo.IEchoService" id="echoService" version="1.0.0"
filter="traceIdFilter"/>
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服务端的测试代码小改为如下：
@Service("echoService")
public class EchoServiceImpl implements IEchoService {
@Override
public String echo(String name) {
String traceId = TraceIdUtils.getTraceId();
System.out.println("name = " + name + ", traceId = " + traceId);
return name;
}
}
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客户端的测试代码片段为：
// *) 第一调用
RpcContext.getContext().setAttachment("traceId", "100001");
service.echo("lilei");
// *) 第二次调用
service.echo("hanmeimei");
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同样的代码, 测试结果如下：
服务端输出:
name = lilei, traceId = 100001
name = hanmeimei, traceId = 100001
客户端输出:
{traceId=100001}
{}
复制代码
符合预期，感觉这个方案就非常优雅了。 RpcContext的attachment依旧被清空(ConsumerContextFilter在自定义的Filter后执行) ，但是每次rpc交互前，traceId会被重新注入，保证跟踪线索透传成功。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持 码农网
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Language Implementation Patterns
Terence Parr / Pragmatic Bookshelf / 2010-1-10 / USD 34.95
Knowing how to create domain-specific languages (DSLs) can give you a huge productivity boost. Instead of writing code in a general-purpose programming language, you can first build a custom language ......一起来看看 《Language Implementation Patterns》 这本书的介绍吧!
