Dubbo系列（四）源碼分析之服務調用
前文介紹了Dubbo中服務暴露的過程，本文繼續介紹服務調用的過程，讓一次服務調用過程連接起來理解。
如果讀者是第一次閱讀本文且對Dubbo SPI沒有了解，可以先閱讀《Dubbo系列（二）源碼分析之SPI機制》、《Dubbo系列（三）源碼分析之服務暴露》。
ps.本文只考慮整合Zookeeper的情況下的默認配置調用過程
讀取配置信息
這裏就不贅述了， [3]Dubbo系列（三）源碼分析之服務暴露 中有介紹。
啓動ReferenceBean來調用服務
ReferenceBean實例化加載過程，核心方法afterPropertiesSet()
public void afterPropertiesSet() throws Exception {
if (getConsumer() == null) {
Map<String, ConsumerConfig> consumerConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ConsumerConfig.class, false, false);
if (consumerConfigMap != null && consumerConfigMap.size() > 0) {
ConsumerConfig consumerConfig = null;
for (ConsumerConfig config : consumerConfigMap.values()) {
if (config.isDefault() == null || config.isDefault().booleanValue()) {
if (consumerConfig != null) {
throw new IllegalStateException("Duplicate consumer configs: " + consumerConfig + " and " + config);
}
consumerConfig = config;
}
}
if (consumerConfig != null) {
setConsumer(consumerConfig);
}
}
}
if (getApplication() == null
&& (getConsumer() == null || getConsumer().getApplication() == null)) {
Map<String, ApplicationConfig> applicationConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ApplicationConfig.class, false, false);
if (applicationConfigMap != null && applicationConfigMap.size() > 0) {
ApplicationConfig applicationConfig = null;
for (ApplicationConfig config : applicationConfigMap.values()) {
if (config.isDefault() == null || config.isDefault().booleanValue()) {
if (applicationConfig != null) {
throw new IllegalStateException("Duplicate application configs: " + applicationConfig + " and " + config);
}
applicationConfig = config;
}
}
if (applicationConfig != null) {
setApplication(applicationConfig);
}
}
}
if (getModule() == null
&& (getConsumer() == null || getConsumer().getModule() == null)) {
Map<String, ModuleConfig> moduleConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ModuleConfig.class, false, false);
if (moduleConfigMap != null && moduleConfigMap.size() > 0) {
ModuleConfig moduleConfig = null;
for (ModuleConfig config : moduleConfigMap.values()) {
if (config.isDefault() == null || config.isDefault().booleanValue()) {
if (moduleConfig != null) {
throw new IllegalStateException("Duplicate module configs: " + moduleConfig + " and " + config);
}
moduleConfig = config;
}
}
if (moduleConfig != null) {
setModule(moduleConfig);
}
}
}
if ((getRegistries() == null || getRegistries().size() == 0)
&& (getConsumer() == null || getConsumer().getRegistries() == null || getConsumer().getRegistries().size() == 0)
&& (getApplication() == null || getApplication().getRegistries() == null || getApplication().getRegistries().size() == 0)) {
Map<String, RegistryConfig> registryConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, RegistryConfig.class, false, false);
if (registryConfigMap != null && registryConfigMap.size() > 0) {
List<RegistryConfig> registryConfigs = new ArrayList<RegistryConfig>();
for (RegistryConfig config : registryConfigMap.values()) {
if (config.isDefault() == null || config.isDefault().booleanValue()) {
registryConfigs.add(config);
}
}
if (registryConfigs != null && registryConfigs.size() > 0) {
super.setRegistries(registryConfigs);
}
}
}
if (getMonitor() == null
&& (getConsumer() == null || getConsumer().getMonitor() == null)
&& (getApplication() == null || getApplication().getMonitor() == null)) {
Map<String, MonitorConfig> monitorConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, MonitorConfig.class, false, false);
if (monitorConfigMap != null && monitorConfigMap.size() > 0) {
MonitorConfig monitorConfig = null;
for (MonitorConfig config : monitorConfigMap.values()) {
if (config.isDefault() == null || config.isDefault().booleanValue()) {
if (monitorConfig != null) {
throw new IllegalStateException("Duplicate monitor configs: " + monitorConfig + " and " + config);
}
monitorConfig = config;
}
}
if (monitorConfig != null) {
setMonitor(monitorConfig);
}
}
}
Boolean b = isInit();
if (b == null && getConsumer() != null) {
b = getConsumer().isInit();
}
if (b != null && b.booleanValue()) {
//獲取引用服務的入口
getObject();
}
}
getObject()鏈路跟蹤
關於client端調用服務的猜想：
- 從註冊中心拉取server端信息
- 對server端信息進行篩選，按照策略選擇服務提供者（負載均衡策略）
- 網絡連接connect到server
com.alibaba.dubbo.config.spring.ReferenceBean#getObject
->com.alibaba.dubbo.config.ReferenceConfig#get
->com.alibaba.dubbo.config.ReferenceConfig#init
->com.alibaba.dubbo.config.ReferenceConfig#createProxy
...
invoker = cluster.join(new StaticDirectory(invokers));
...
// 創建服務代理
return (T) proxyFactory.getProxy(invoker);
那麼出現兩條分支：
- cluster.join()
- (T) proxyFactory.getProxy(invoker)
進入分支1:
先弄清楚cluster怎麼生成
private static final Cluster cluster = ExtensionLoader.getExtensionLoader(Cluster.class).getAdaptiveExtension();
根據SPI機制，結合前面invoker中的url推斷出會調用MockClusterWrapper#join
@SPI(FailoverCluster.NAME)
public interface Cluster {
/**
* Merge the directory invokers to a virtual invoker.
*
* @param <T>
* @param directory
* @return cluster invoker
* @throws RpcException
*/
@Adaptive
<T> Invoker<T> join(Directory<T> directory) throws RpcException;
}
MockClusterWrapper#join，返回MockClusterInvoker(FailoverClusterInvoker())。
回溯後invoker=MockClusterWrapper，並執行(T) proxyFactory.getProxy(invoker);
進入分支2：
先弄明白proxyFactory
private static final ProxyFactory proxyFactory = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();
根據SPI機制，推斷出實現類對象爲StubProxyFactoryWrapper(JavassistProxyFactory())
com.alibaba.dubbo.rpc.proxy.wrapper.StubProxyFactoryWrapper#getProxy
這裏執行了export()，將consumer信息註冊到註冊中心
->com.alibaba.dubbo.rpc.proxy.AbstractProxyFactory#getProxy(com.alibaba.dubbo.rpc.Invoker<T>)
->com.alibaba.dubbo.rpc.proxy.javassist.JavassistProxyFactory#getProxy
這裏執行真正的實例化方法，以Javassist原生代理方式生成代理對象並傳入
new InvokerInvocationHandler(invoker)
此InvokerInvocationHandler真正完成服務調用功能
com.alibaba.dubbo.rpc.proxy.InvokerInvocationHandler#invoke
由前面傳入的invoker可知
->com.alibaba.dubbo.rpc.cluster.support.MockClusterInvoker#invoke
Mock是用於做服務降級
public Result invoke(Invocation invocation) throws RpcException {
Result result = null;
String value = directory.getUrl().getMethodParameter(invocation.getMethodName(), Constants.MOCK_KEY, Boolean.FALSE.toString()).trim();
if (value.length() == 0 || value.equalsIgnoreCase("false")) {
//no mock
result = this.invoker.invoke(invocation);
} else if (value.startsWith("force")) {
if (logger.isWarnEnabled()) {
logger.info("force-mock: " + invocation.getMethodName() + " force-mock enabled , url : " + directory.getUrl());
}
//force:direct mock
result = doMockInvoke(invocation, null);
} else {
//fail-mock
try {
result = this.invoker.invoke(invocation);
} catch (RpcException e) {
if (e.isBiz()) {
throw e;
} else {
if (logger.isWarnEnabled()) {
logger.info("fail-mock: " + invocation.getMethodName() + " fail-mock enabled , url : " + directory.getUrl(), e);
}
result = doMockInvoke(invocation, e);
}
}
}
return result;
}
->進入this.invoker.invoke(invocation);此時調用FailoverClusterInvoker#invoke
->進入模板方法com.alibaba.dubbo.rpc.cluster.support.AbstractClusterInvoker#invoke
public Result invoke(final Invocation invocation) throws RpcException {
checkWhetherDestroyed();
LoadBalance loadbalance;
List<Invoker<T>> invokers = list(invocation);
if (invokers != null && invokers.size() > 0) {
loadbalance = ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(invokers.get(0).getUrl()
.getMethodParameter(invocation.getMethodName(), Constants.LOADBALANCE_KEY, Constants.DEFAULT_LOADBALANCE));
} else {
loadbalance = ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(Constants.DEFAULT_LOADBALANCE);
}
RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
return doInvoke(invocation, invokers, loadbalance);
}
->進入FailoverClusterInvoker#doInvoke
public Result doInvoke(Invocation invocation, final List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
List<Invoker<T>> copyinvokers = invokers;
checkInvokers(copyinvokers, invocation);
int len = getUrl().getMethodParameter(invocation.getMethodName(), Constants.RETRIES_KEY, Constants.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++) {
//重試時，進行重新選擇，避免重試時invoker列表已發生變化.
//注意：如果列表發生了變化，那麼invoked判斷會失效，因爲invoker示例已經改變
if (i > 0) {
checkWhetherDestroyed();
copyinvokers = list(invocation);
//重新檢查一下
checkInvokers(copyinvokers, invocation);
}
//負載均衡的實現點
Invoker<T> invoker = select(loadbalance, invocation, copyinvokers, invoked);
invoked.add(invoker);
RpcContext.getContext().setInvokers((List) invoked);
try {
//執行服務的調用
Result result = invoker.invoke(invocation);
if (le != null && logger.isWarnEnabled()) {
logger.warn("Although retry the method " + invocation.getMethodName()
+ " 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 != null ? le.getCode() : 0, "Failed to invoke the method "
+ invocation.getMethodName() + " 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 != null ? le.getMessage() : ""), le != null && le.getCause() != null ? le.getCause() : le);
}
->com.alibaba.dubbo.rpc.protocol.AbstractInvoker#invoke
->com.alibaba.dubbo.rpc.protocol.dubbo.DubboInvoker#doInvoke
protected Result doInvoke(final Invocation invocation) throws Throwable {
RpcInvocation inv = (RpcInvocation) invocation;
final String methodName = RpcUtils.getMethodName(invocation);
inv.setAttachment(Constants.PATH_KEY, getUrl().getPath());
inv.setAttachment(Constants.VERSION_KEY, version);
ExchangeClient currentClient;
//clients則是當前持有的遠程服務器
if (clients.length == 1) {
currentClient = clients[0];
} else {
currentClient = clients[index.getAndIncrement() % clients.length];
}
try {
boolean isAsync = RpcUtils.isAsync(getUrl(), invocation);
boolean isOneway = RpcUtils.isOneway(getUrl(), invocation);
int timeout = getUrl().getMethodParameter(methodName, Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
if (isOneway) {
boolean isSent = getUrl().getMethodParameter(methodName, Constants.SENT_KEY, false);
currentClient.send(inv, isSent);
RpcContext.getContext().setFuture(null);
return new RpcResult();
} else if (isAsync) {
ResponseFuture future = currentClient.request(inv, timeout);
RpcContext.getContext().setFuture(new FutureAdapter<Object>(future));
return new RpcResult();
} else {
RpcContext.getContext().setFuture(null);
//發起rpc請求
return (Result) currentClient.request(inv, timeout).get();
}
} 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);
}
}
猜想三得到了驗證。
沿着currentClient.request(inv, timeout);，深入…
看到了com.alibaba.dubbo.remoting.transport.netty.NettyChannel#send
終於，通過NettyChannel進行了通信。
那麼，從註冊中心拉取服務列表信息是在哪裏完成的呢？
繼續回去找，在com.alibaba.dubbo.rpc.cluster.support.AbstractClusterInvoker#invoke找到List<Invoker<T>> invokers = list(invocation);，通過跟蹤鏈路和分析源碼，瞭解到一個invoker對應一個服務的調用器，那麼拉取服務列表信息的操作必然出現在獲取所有的調用器的點。
protected List<Invoker<T>> list(Invocation invocation) throws RpcException {
List<Invoker<T>> invokers = directory.list(invocation);
return invokers;
}
進入com.alibaba.dubbo.rpc.cluster.directory.AbstractDirectory#list
public List<Invoker<T>> list(Invocation invocation) throws RpcException {
if (destroyed) {
throw new RpcException("Directory already destroyed .url: " + getUrl());
}
List<Invoker<T>> invokers = doList(invocation);
List<Router> localRouters = this.routers; // local reference
if (localRouters != null && localRouters.size() > 0) {
for (Router router : localRouters) {
try {
if (router.getUrl() == null || router.getUrl().getParameter(Constants.RUNTIME_KEY, true)) {
invokers = router.route(invokers, getConsumerUrl(), invocation);
}
} catch (Throwable t) {
logger.error("Failed to execute router: " + getUrl() + ", cause: " + t.getMessage(), t);
}
}
}
return invokers;
}
繼續進入com.alibaba.dubbo.registry.integration.RegistryDirectory#doList
public List<Invoker<T>> doList(Invocation invocation) {
if (forbidden) {
// 1. 沒有服務提供者 2. 服務提供者被禁用
throw new RpcException(RpcException.FORBIDDEN_EXCEPTION,
"No provider available from registry " + getUrl().getAddress() + " for service " + getConsumerUrl().getServiceKey() + " on consumer " + NetUtils.getLocalHost()
+ " use dubbo version " + Version.getVersion() + ", may be providers disabled or not registered ?");
}
List<Invoker<T>> invokers = null;
Map<String, List<Invoker<T>>> localMethodInvokerMap = this.methodInvokerMap; // local reference
if (localMethodInvokerMap != null && localMethodInvokerMap.size() > 0) {
String methodName = RpcUtils.getMethodName(invocation);
Object[] args = RpcUtils.getArguments(invocation);
if (args != null && args.length > 0 && args[0] != null
&& (args[0] instanceof String || args[0].getClass().isEnum())) {
invokers = localMethodInvokerMap.get(methodName + "." + args[0]); // 可根據第一個參數枚舉路由
}
if (invokers == null) {
invokers = localMethodInvokerMap.get(methodName);
}
if (invokers == null) {
invokers = localMethodInvokerMap.get(Constants.ANY_VALUE);
}
if (invokers == null) {
Iterator<List<Invoker<T>>> iterator = localMethodInvokerMap.values().iterator();
if (iterator.hasNext()) {
invokers = iterator.next();
}
}
}
return invokers == null ? new ArrayList<Invoker<T>>(0) : invokers;
}
雖然找到了invokers的獲取路徑，但是沒有找到從註冊中心拉取的代碼，不過，明白了基本原理，就很容易猜中了。最後，在export()中可以跟蹤到com.alibaba.dubbo.registry.integration.RegistryProtocol#export，然後到ZookeeperRegistry，發現在ZookeeperRegistry的實例化裏面做了實現。而在RegistryDirectory中找到public void setRegistry(Registry registry) { this.registry = registry;}，熟悉嗎？注入了一個自適應的Registry，在這裏，由於我的配置是zookeeper，就是ZookeeperRegistry
public ZookeeperRegistry(URL url, ZookeeperTransporter zookeeperTransporter) {
super(url);
if (url.isAnyHost()) {
throw new IllegalStateException("registry address == null");
}
String group = url.getParameter(Constants.GROUP_KEY, DEFAULT_ROOT);
if (!group.startsWith(Constants.PATH_SEPARATOR)) {
group = Constants.PATH_SEPARATOR + group;
}
this.root = group;
zkClient = zookeeperTransporter.connect(url);
zkClient.addStateListener(new StateListener() {
public void stateChanged(int state) {
if (state == RECONNECTED) {
try {
recover();
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
}
}
});
}
猜想一也得到了驗證。
最後，服務端接受消息後的處理鏈路：
NettyHandler.messageReceived
->handler.received
->MultiMessageHandler(HeartbeatHandler(AllChannelHandler(DecodeHandler))).received
MultiMessageHandler: 複合消息處理
HeartbeatHandler：心跳消息處理，接收心跳併發送心跳響應
AllChannelHandler：業務線程轉化處理器，把接收到的消息封裝成ChannelEventRunnable：可執行任務給線程池處理
DecodeHandler：業務解碼處理器
->ExchangeHandlerAdaptive.replay(DubboProtocol)
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 需要處理高版本調用低版本的問題
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());
return invoker.invoke(inv);
}
throw new RemotingException(channel, "Unsupported request: " + message == null ? null : (message.getClass().getName() + ": " + message) + ", channel: consumer: " + channel.getRemoteAddress() + " --> provider: " + channel.getLocalAddress());
}
->最終調用invoker.invoke()，而該invoker即是服務暴露時生產的InvokerDelegete(AbstractProxyInvoker(Wrapper.invokeMethod))
小結
源碼閱讀過程很容易混亂，如果條件允許，希望讀者能從零搭建dubbo項目後，從程序入口一步一步深入，反覆的閱讀，就不會暈車嘍！