例子
示例中通过Spring上下文获取到了DemoService实例，在上篇文章Dubbo Consumer引用服务中我们已经了解引用服务，创建invoker，创建代理对象的流程，这里的DemoService实例就是创建的代理对象，然后通过代理对象调用sayHello方法。
public class DubboConsumer {
public static void main(String[] args) {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring/dubbo-demo-consumer.xml");
context.start();
DemoService demoService = context.getBean("demoService", DemoService.class);
String hello = demoService.sayHello("world");
System.out.println(hello);
}
}
DubboInvokerInvocationHandler实现了InvocationHandler接口，并且重写了invoke方法，当调用sayHello方法实际上就会调用到InvokerInvocationHandler的invoke方法。代码如下：
public class InvokerInvocationHandler implements InvocationHandler {
private static final Logger logger = LoggerFactory.getLogger(InvokerInvocationHandler.class);
private final Invoker<?> invoker;
private ConsumerModel consumerModel;
public InvokerInvocationHandler(Invoker<?> handler) {
this.invoker = handler;
String serviceKey = invoker.getUrl().getServiceKey();
if (serviceKey != null) {
this.consumerModel = ApplicationModel.getConsumerModel(serviceKey);
}
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.getDeclaringClass() == Object.class) {
return method.invoke(invoker, args);
}
String methodName = method.getName();
Class<?>[] parameterTypes = method.getParameterTypes();
// 如果没有参数走下边逻辑，会判断是否是toString，hashCode，equals，$destroy等方法，这里sayHello跳过
if (parameterTypes.length == 0) {
if ("toString".equals(methodName)) {
return invoker.toString();
} else if ("$destroy".equals(methodName)) {
invoker.destroy();
return null;
} else if ("hashCode".equals(methodName)) {
return invoker.hashCode();
}
} else if (parameterTypes.length == 1 && "equals".equals(methodName)) {
return invoker.equals(args[0]);
}
// 创建RpcInvocation实例
RpcInvocation rpcInvocation = new RpcInvocation(method, invoker.getInterface().getName(), args);
// serviceKey 这里是 org.apache.dubbo.samples.serialization.api.DemoService
String serviceKey = invoker.getUrl().getServiceKey();
rpcInvocation.setTargetServiceUniqueName(serviceKey);
if (consumerModel != null) {
rpcInvocation.put(Constants.CONSUMER_MODEL, consumerModel);
rpcInvocation.put(Constants.METHOD_MODEL, consumerModel.getMethodModel(method));
}
return invoker.invoke(rpcInvocation).recreate();
}
}
这里的代理proxy包含了在服务注册，订阅阶段所产生的所有配置信息以及Invoker，Invoker会被装饰成调用链，proxy包含了Invoker,Directory,ConsumerModel,ReferenceConfig等等，如下图：
执行invoker.invoke处理流程
下面会按照代码执行流程，简单介绍一下一个请求的处理流程，所经介绍类的顺序即代表了代码所执行的流程顺序。
MockClusterInvoker： 首先会走到这个类中，因为没有mock，所以直接向下走。
AbstractCluster： 这里会添加一个ClusterInterceptor拦截器，在调用前后做一些处理，这个不细说。
@Override
public Result invoke(Invocation invocation) throws RpcException {
Result asyncResult;
try {
// 调用前
interceptor.before(next, invocation);
// 通过ClusterInterceptor#intercept方法执行clusterInvoker的调用，这里clusterInvoker默认的使用FailoverClusterInvoker
asyncResult = interceptor.intercept(next, invocation);
} catch (Exception e) {
// onError callback
if (interceptor instanceof ClusterInterceptor.Listener) {
ClusterInterceptor.Listener listener = (ClusterInterceptor.Listener) interceptor;
listener.onError(e, clusterInvoker, invocation);
}
throw e;
} finally {
// 调用后
interceptor.after(next, invocation);
}
return asyncResult.whenCompleteWithContext((r, t) -> {
// onResponse callback
if (interceptor instanceof ClusterInterceptor.Listener) {
ClusterInterceptor.Listener listener = (ClusterInterceptor.Listener) interceptor;
if (t == null) {
listener.onMessage(r, clusterInvoker, invocation);
} else {
listener.onError(t, clusterInvoker, invocation);
}
}
});
}
ClusterInterceptor： 调用拦截器，在拦截器的intercept方法中会执行AbstractClusterInvoker#invoke方法。
@SPI
public interface ClusterInterceptor {
void before(AbstractClusterInvoker<?> clusterInvoker, Invocation invocation);
void after(AbstractClusterInvoker<?> clusterInvoker, Invocation invocation);
/**
* Does not need to override this method, override {@link #before(AbstractClusterInvoker, Invocation)}
* and {@link #after(AbstractClusterInvoker, Invocation)}, methods to add your own logic expected to be
* executed before and after invoke.
*
* @param clusterInvoker
* @param invocation
* @return
* @throws RpcException
*/
default Result intercept(AbstractClusterInvoker<?> clusterInvoker, Invocation invocation) throws RpcException {
// 走到AbstractClusterInvoker#invoke方法
return clusterInvoker.invoke(invocation);
}
interface Listener {
void onMessage(Result appResponse, AbstractClusterInvoker<?> clusterInvoker, Invocation invocation);
void onError(Throwable t, AbstractClusterInvoker<?> clusterInvoker, Invocation invocation);
}
}
AbstractClusterInvoker
这里有负载均衡操作暂时不关心，继续调用doInvoke，实际上就是执行子类的实现，这里默认执行子类FailoverClusterInvoker的doInvoker。
@Override
public Result invoke(final Invocation invocation) throws RpcException {
checkWhetherDestroyed();
// binding attachments into invocation.
Map<String, Object> contextAttachments = RpcContext.getContext().getObjectAttachments();
if (contextAttachments != null && contextAttachments.size() != 0) {
((RpcInvocation) invocation).addObjectAttachments(contextAttachments);
}
List<Invoker<T>> invokers = list(invocation);
LoadBalance loadbalance = initLoadBalance(invokers, invocation);
RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
// 默认执行子类`FailoverClusterInvoker`的`doInvoker`。
return doInvoke(invocation, invokers, loadbalance);
}
FailoverClusterInvoker#doInvoke
执行流程 AbstractClusterInvoker#invoke -》 FailoverClusterInvoker#doInvoke -》 AbstractClusterInvoker#select选择一个Invoker -》 执行Invoker调用链
然后会通过装饰器模式，构造一个Invoker的调用链，最终会执行DubboInvoker的doInvoke方法；
Invoker调用链如下：
- ProtocolFilterWrapper
- - ListenerInvokerWrapper
- - - AsyncToSyncInvoker
- - - - DubboInvoker
@Override
@SuppressWarnings({"unchecked", "rawtypes"})
public Result doInvoke(Invocation invocation, final List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
List<Invoker<T>> copyInvokers = invokers;
checkInvokers(copyInvokers, invocation);
String methodName = RpcUtils.getMethodName(invocation);
int len = getUrl().getMethodParameter(methodName, RETRIES_KEY, DEFAULT_RETRIES) + 1;
if (len <= 0) {
len = 1;
}
// retry loop.
RpcException le = null; // last exception.
List<Invoker<T>> invoked = new ArrayList<Invoker<T>>(copyInvokers.size()); // invoked invokers.
Set<String> providers = new HashSet<String>(len);
for (int i = 0; i < len; i++) {
//Reselect before retry to avoid a change of candidate `invokers`.
//NOTE: if `invokers` changed, then `invoked` also lose accuracy.
if (i > 0) {
checkWhetherDestroyed();
copyInvokers = list(invocation);
// check again
checkInvokers(copyInvokers, invocation);
}
Invoker<T> invoker = select(loadbalance, invocation, copyInvokers, invoked);
invoked.add(invoker);
RpcContext.getContext().setInvokers((List) invoked);
try {
// 装饰器模式 装饰invoker调用链
// - ProtocolFilterWrapper
// - - ListenerInvokerWrapper
// - - - AsyncToSyncInvoker
// - - - - DubboInvoker
Result result = invoker.invoke(invocation);
if (le != null && logger.isWarnEnabled()) {
logger.warn("Although retry the method " + methodName
+ " in the service " + getInterface().getName()
+ " was successful by the provider " + invoker.getUrl().getAddress()
+ ", but there have been failed providers " + providers
+ " (" + providers.size() + "/" + copyInvokers.size()
+ ") from the registry " + directory.getUrl().getAddress()
+ " on the consumer " + NetUtils.getLocalHost()
+ " using the dubbo version " + Version.getVersion() + ". Last error is: "
+ le.getMessage(), le);
}
return result;
} catch (RpcException e) {
if (e.isBiz()) { // biz exception.
throw e;
}
le = e;
} catch (Throwable e) {
le = new RpcException(e.getMessage(), e);
} finally {
providers.add(invoker.getUrl().getAddress());
}
}
throw new RpcException(le.getCode(), "Failed to invoke the method "
+ methodName + " in the service " + getInterface().getName()
+ ". Tried " + len + " times of the providers " + providers
+ " (" + providers.size() + "/" + copyInvokers.size()
+ ") from the registry " + directory.getUrl().getAddress()
+ " on the consumer " + NetUtils.getLocalHost() + " using the dubbo version "
+ Version.getVersion() + ". Last error is: "
+ le.getMessage(), le.getCause() != null ? le.getCause() : le);
}
}
DubboInvoker#doInvoke方法： 敲重点，最终会通过该方法完成远程调用以及异步调用结果的封装
@Override
protected Result doInvoke(final Invocation invocation) throws Throwable {
RpcInvocation inv = (RpcInvocation) invocation;
final String methodName = RpcUtils.getMethodName(invocation);
inv.setAttachment(PATH_KEY, getUrl().getPath());
inv.setAttachment(VERSION_KEY, version);
ExchangeClient currentClient;
// 如果clients数量是1 直接使用第一个，否则的话就取第用自增值与clients数量做取余运算个
if (clients.length == 1) {
currentClient = clients[0];
} else {
currentClient = clients[index.getAndIncrement() % clients.length];
}
try {
boolean isOneway = RpcUtils.isOneway(getUrl(), invocation);
int timeout = calculateTimeout(invocation, methodName);
// 单向发送，不用关心返回值
if (isOneway) {
boolean isSent = getUrl().getMethodParameter(methodName, Constants.SENT_KEY, false);
currentClient.send(inv, isSent);
return AsyncRpcResult.newDefaultAsyncResult(invocation);
} else {
// 异步调用
// 回调线程
ExecutorService executor = getCallbackExecutor(getUrl(), inv);
// 在requset中设置回调线程， 这里使用CompletableFuture 设置回调，thenApply的目的就是将异步结果拿过来，最后会将异步结果转成AppResponse
CompletableFuture<AppResponse> appResponseFuture =
currentClient.request(inv, timeout, executor).thenApply(obj -> (AppResponse) obj);
// save for 2.6.x compatibility, for example, TraceFilter in Zipkin uses com.alibaba.xxx.FutureAdapter
// 这里会讲 CompletableFuture封装成FutureAdapter，并且绑定到FutureContext的futureTL中
FutureContext.getContext().setCompatibleFuture(appResponseFuture);
AsyncRpcResult result = new AsyncRpcResult(appResponseFuture, inv);
result.setExecutor(executor);
return result;
}
} catch (TimeoutException e) {
throw new RpcException(RpcException.TIMEOUT_EXCEPTION, "Invoke remote method timeout. method: " + invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
} catch (RemotingException e) {
throw new RpcException(RpcException.NETWORK_EXCEPTION, "Failed to invoke remote method: " + invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
}
}
AsyncToSyncInvoker#invoke获取RPC调用结果
@Override
public Result invoke(Invocation invocation) throws RpcException {
Result asyncResult = invoker.invoke(invocation);
try {
if (InvokeMode.SYNC == ((RpcInvocation) invocation).getInvokeMode()) {
/**
* NOTICE!
* must call {@link java.util.concurrent.CompletableFuture#get(long, TimeUnit)} because
* {@link java.util.concurrent.CompletableFuture#get()} was proved to have serious performance drop.
*/
// 获取调用结果
asyncResult.get(Integer.MAX_VALUE, TimeUnit.MILLISECONDS);
}
} catch (InterruptedException e) {
throw new RpcException("Interrupted unexpectedly while waiting for remote result to return! method: " +
invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
} catch (ExecutionException e) {
Throwable t = e.getCause();
if (t instanceof TimeoutException) {
throw new RpcException(RpcException.TIMEOUT_EXCEPTION, "Invoke remote method timeout. method: " +
invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
} else if (t instanceof RemotingException) {
throw new RpcException(RpcException.NETWORK_EXCEPTION, "Failed to invoke remote method: " +
invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
} else {
throw new RpcException(RpcException.UNKNOWN_EXCEPTION, "Fail to invoke remote method: " +
invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
}
} catch (Throwable e) {
throw new RpcException(e.getMessage(), e);
}
return asyncResult;
}
AsyncRpcResult#get调用结果： 通过CompletableFuture的get方法获取RPC调用的结果。
@Override
public Result get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
if (executor != null && executor instanceof ThreadlessExecutor) {
ThreadlessExecutor threadlessExecutor = (ThreadlessExecutor) executor;
threadlessExecutor.waitAndDrain();
}
return responseFuture.get(timeout, unit);
}
总结
Dubbo通过代理对象以及Invoker实现了远程调用，Dubbo实现了InvocationHandler接口重写了invoke方法，在调用代理对象方法时会调用invoke，远程调用分为oneWay（单向）和异步/同步；单向发送不关心发送结果，发送请求后就直接返回，异步/同步发送需要处理结果，通过Future的get取响应结果；Dubbo提供了远程调用的容错处理，包括调用策略，路由，负载均衡等
