Dubbo中服务消费者和服务提供者之间的请求和响应过程

服务提供者初始化完成之后,对外暴露Exporter。服务消费者初始化完成之后,得到的是Proxy代理,方法调用的时候就是调用代理。

服务消费者经过初始化之后,得到的是一个动态代理类,InvokerInvocationHandler,包含MockClusterInvoker,MockClusterInvoker包含一个RegistryDirectory和FailoverClusterInvoker。

Java动态代理,每一个动态代理类都必须要实现InvocationHandler这个接口,并且每一个代理类的实例都关联到了一个handler,当我们通过代理对象调用一个方法的时候,这个方法就会被转发为由实现了InvocationHandler这个接口的类的invoke方法来进行调用。

服务消费者发起调用请求

InvokerInvocationHandler实现了InvocationHandler接口,当我们调用helloService.sayHello();的时候,实际上会调用invoke()方法:

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//proxy是代理的真实对象
//method调用真实对象的方法
//args调用真实对象的方法的参数
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//方法名sayHello
String methodName = method.getName();
//参数类型
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]);
}
//invoker是MockClusterInvoker
//首先new RpcInvocation
//然后invoker.invoke
//最后recreate
//返回结果
return invoker.invoke(new RpcInvocation(method, args)).recreate();
}

先看下new RpcInvocation,Invocation是会话域,它持有调用过程中的变量,比如方法名,参数类型等。

接着是invoker.invoke(),这里invoker是MockClusterInvoker,进入MockClusterInvoker.invoker():

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public Result invoke(Invocation invocation) throws RpcException {
Result result = null;
//获取mock属性的值,我们没有配置,默认false
String value = directory.getUrl().getMethodParameter(invocation.getMethodName(), Constants.MOCK_KEY, Boolean.FALSE.toString()).trim();
if (value.length() == 0 || value.equalsIgnoreCase("false")){
//这里invoker是FailoverClusterInvoker
result = this.invoker.invoke(invocation);
} else if (value.startsWith("force")) {
//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 {
result = doMockInvoke(invocation, e);
}
}
}
return result;
}

result = this.invoker.invoke(invocation);这里invoker是FailoverClusterInvoker,会首先进入AbstractClusterInvoker的invoke方法:

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public Result invoke(final Invocation invocation) throws RpcException {
//检查是否被销毁
checkWheatherDestoried();
LoadBalance loadbalance;
//根据invocation中的参数来获取所有的invoker列表
List<Invoker<T>> invokers = list(invocation);
if (invokers != null && invokers.size() > 0) {
//我们没有配置负载均衡的参数,默认使用random
//这里得到的是RandomLoadBalance
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);
}
//如果是异步操作默认添加invocation id
RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
//这里是子类实现,FailoverClusterInvoker中,执行调用
return doInvoke(invocation, invokers, loadbalance);
}

FailoverClusterInvoker.doInvoke():

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public Result doInvoke(Invocation invocation, final List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
List<Invoker<T>> copyinvokers = invokers;
//检查invokers是否为空
checkInvokers(copyinvokers, invocation);
//重试次数
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.
//已经调用过的invoker
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++) {
//重试时,进行重新选择,避免重试时invoker列表已发生变化.
//注意:如果列表发生了变化,那么invoked判断会失效,因为invoker示例已经改变
if (i > 0) {
checkWheatherDestoried();
copyinvokers = list(invocation);
//重新检查一下
checkInvokers(copyinvokers, invocation);
}
//使用负载均衡选择invoker.(负载均衡咱先不做解释)
Invoker<T> invoker = select(loadbalance, invocation, copyinvokers, invoked);
invoked.add(invoker);
//添加到以调用过的列表中
RpcContext.getContext().setInvokers((List)invoked);
try {
//开始调用,返回结果
Result result = invoker.invoke(invocation);
return result;
} catch (RpcException e) {。。。 } finally {
providers.add(invoker.getUrl().getAddress());
}
}
throw new RpcException(。。。);
}

Result result = invoker.invoke(invocation);调用并返回结果,会首先进入InvokerWrapper,然后进入ListenerInvokerWrapper的invoke方法,接着进入AbstractInvoker的invoke:

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public Result invoke(Invocation inv) throws RpcException {
if(destroyed) {
throw new RpcException(。。。);
}
//转成RpcInvocation
RpcInvocation invocation = (RpcInvocation) inv;
invocation.setInvoker(this);
if (attachment != null && attachment.size() > 0) {
invocation.addAttachmentsIfAbsent(attachment);
}
Map<String, String> context = RpcContext.getContext().getAttachments();
if (context != null) {
invocation.addAttachmentsIfAbsent(context);
}
if (getUrl().getMethodParameter(invocation.getMethodName(), Constants.ASYNC_KEY, false)){
invocation.setAttachment(Constants.ASYNC_KEY, Boolean.TRUE.toString());
}
//异步的话,需要添加id
RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
try {
//这里是DubboInvoker
return doInvoke(invocation);
} catch (InvocationTargetException e) { }
}

DubboInvoker.doInvoke():

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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;
//在初始化的时候,引用服务的过程中会保存一个连接到服务端的Client
if (clients.length == 1) {
currentClient = clients[0];
} else {
currentClient = clients[index.getAndIncrement() % clients.length];
}
try {
//异步标志
boolean isAsync = RpcUtils.isAsync(getUrl(), invocation);
//单向标志
boolean isOneway = RpcUtils.isOneway(getUrl(), invocation);
int timeout = getUrl().getMethodParameter(methodName, Constants.TIMEOUT_KEY,Constants.DEFAULT_TIMEOUT);
//单向的,反送完不管结果
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) {//异步的,发送完需要得到Future
ResponseFuture future = currentClient.request(inv, timeout) ;
RpcContext.getContext().setFuture(new FutureAdapter<Object>(future));
return new RpcResult();
} else {//同步调用,我们这里使用的这种方式
RpcContext.getContext().setFuture(null);
//HeaderExchangeClient
return (Result) currentClient.request(inv, timeout).get();
}
} catch (TimeoutException e) {。。。}
}

我们这里使用的是同步调用,看(Result) currentClient.request(inv, timeout).get();方法,这里的client是ReferenceCountExchangeClient,直接调用HeaderExchangeClient的request方法:

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public ResponseFuture request(Object request, int timeout) throws RemotingException {
//这里的Channel是HeaderExchangeChannel
return channel.request(request, timeout);
}

进入HeaderExchangeChannel的request方法:

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public ResponseFuture request(Object request, int timeout) throws RemotingException {
if (closed) {
throw new RemotingException(。。。);
}
//创建一个请求头
Request req = new Request();
req.setVersion("2.0.0");
req.setTwoWay(true);
//这里request参数里面保存着
//methodName = "sayHello"
//parameterTypes = {Class[0]@2814}
//arguments = {Object[0]@2768}
//attachments = {HashMap@2822} size = 4
//invoker = {DubboInvoker@2658}
req.setData(request);
DefaultFuture future = new DefaultFuture(channel, req, timeout);
try{
//这里的channel是NettyClient
//发送请求
channel.send(req);
}catch (RemotingException e) {
future.cancel();
throw e;
}
return future;
}

channel.send(req),首先会调用AbstractPeer的send方法:

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//子类处理,接着是AbstractClient执行发送
public void send(Object message) throws RemotingException {
send(message, url.getParameter(Constants.SENT_KEY, false));
}

AbstractClient执行发送:

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public void send(Object message, boolean sent) throws RemotingException {
//重连
if (send_reconnect && !isConnected()){
connect();
}
//先获取Channel,是在NettyClient中实现的
Channel channel = getChannel();
//TODO getChannel返回的状态是否包含null需要改进
if (channel == null || ! channel.isConnected()) {
throw new RemotingException(this, "message can not send, because channel is closed . url:" + getUrl());
}
channel是NettyChannel
channel.send(message, sent);
}

channel.send(message, sent);首先经过AbstractChannel的send方法处理,只是判断是否关闭了,然后是NettyChannel的send来继续处理,这里就把消息发送到服务端了:

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public void send(Object message, boolean sent) throws RemotingException {
super.send(message, sent);

boolean success = true;
int timeout = 0;
try {
//交给netty处理
ChannelFuture future = channel.write(message);
if (sent) {
timeout = getUrl().getPositiveParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
success = future.await(timeout);
}
Throwable cause = future.getCause();
if (cause != null) {
throw cause;
}
} catch (Throwable e) {
throw new RemotingException(this, "Failed to send message " + message + " to " + getRemoteAddress() + ", cause: " + e.getMessage(), e);
}

if(! success) {
throw new RemotingException(this, "Failed to send message " + message + " to " + getRemoteAddress()
+ "in timeout(" + timeout + "ms) limit");
}
}

服务提供者处理并响应请求

服务端已经打开端口并监听请求的到来,当服务消费者发送调用请求的时候,经过Netty的处理后会到dubbo中的codec相关方法中先进行解码,入口是NettyCodecAdapter.messageReceived(),关于这个方法的代码在dubbo编解码的那篇文章中已经分析过,不再重复。经过解码之后,会进入到NettyHandler.messageReceived()方法:

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public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
//获取channel
NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
try {
//这里handler是NettyServer
handler.received(channel, e.getMessage());
} finally {
NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
}
}

接着会进入AbstractPeer的received方法:

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public void received(Channel ch, Object msg) throws RemotingException {
if (closed) {
return;
}
//这里是MultiMessageHandler
handler.received(ch, msg);
}

进入MultiMessageHandler的received方法:

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public void received(Channel channel, Object message) throws RemotingException {
//是多消息的话,使用多消息处理器处理
if (message instanceof MultiMessage) {
MultiMessage list = (MultiMessage)message;
for(Object obj : list) {
handler.received(channel, obj);
}
} else {
//这里是HeartbeatHandler
handler.received(channel, message);
}
}

进入HeartbeatHandler的received方法:

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public void received(Channel channel, Object message) throws RemotingException {
setReadTimestamp(channel);
//心跳请求处理
if (isHeartbeatRequest(message)) {
Request req = (Request) message;
if (req.isTwoWay()) {
Response res = new Response(req.getId(), req.getVersion());
res.setEvent(Response.HEARTBEAT_EVENT);
channel.send(res);
}
return;
}
//心跳回应消息处理
if (isHeartbeatResponse(message)) {
return;
}
//这里是AllChannelHandler
handler.received(channel, message);
}

继续进入AllChannelHandler的received方法:

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public void received(Channel channel, Object message) throws RemotingException {
//获取线程池执行
ExecutorService cexecutor = getExecutorService();
try {
//handler是DecodeHandler
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.RECEIVED, message));
} catch (Throwable t) { }
}

这里会去启动新线程执行ChannelEventRunnable的run方法,接着去调用DecodeHandler的received方法:

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public void received(Channel channel, Object message) throws RemotingException {
//不清楚啥意思
if (message instanceof Decodeable) {
decode(message);
}
//解码请求类型
if (message instanceof Request) {
decode(((Request)message).getData());
}
//解码响应类型
if (message instanceof Response) {
decode( ((Response)message).getResult());
}
//解码之后到HeaderExchangeHandler中处理
handler.received(channel, message);
}

解码之后到HeaderExchangeHandler的received方法:

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public void received(Channel channel, Object message) throws RemotingException {
channel.setAttribute(KEY_READ_TIMESTAMP, System.currentTimeMillis());
ExchangeChannel exchangeChannel = HeaderExchangeChannel.getOrAddChannel(channel);
try {
//request类型的消息
if (message instanceof Request) {
Request request = (Request) message;
if (request.isEvent()) {//判断心跳还是正常请求
// 处理心跳
handlerEvent(channel, request);
} else {//正常的请求
//需要返回
if (request.isTwoWay()) {
//处理请求,并构造响应信息
Response response = handleRequest(exchangeChannel, request);
//NettyChannel,发送响应信息
channel.send(response);
} else {//不需要返回的处理
handler.received(exchangeChannel, request.getData());
}
}
} else if (message instanceof Response) {//response类型的消息
handleResponse(channel, (Response) message);
} else if (message instanceof String) {
if (isClientSide(channel)) {
Exception e = new Exception("Dubbo client can not supported string message: " + message + " in channel: " + channel + ", url: " + channel.getUrl());
} else {//telnet类型
String echo = handler.telnet(channel, (String) message);
if (echo != null && echo.length() > 0) {
channel.send(echo);
}
}
} else {
handler.received(exchangeChannel, message);
}
} finally {
HeaderExchangeChannel.removeChannelIfDisconnected(channel);
}
}

先看下处理请求,并构造响应信息:

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Response handleRequest(ExchangeChannel channel, Request req) throws RemotingException {
Response res = new Response(req.getId(), req.getVersion());
if (req.isBroken()) {
Object data = req.getData();

String msg;
if (data == null) msg = null;
else if (data instanceof Throwable) msg = StringUtils.toString((Throwable) data);
else msg = data.toString();
res.setErrorMessage("Fail to decode request due to: " + msg);
res.setStatus(Response.BAD_REQUEST);

return res;
}
// find handler by message class.
Object msg = req.getData();
try {
//处理请求数据,handler是DubboProtocol中的new的一个ExchangeHandlerAdapter
Object result = handler.reply(channel, msg);
res.setStatus(Response.OK);
res.setResult(result);
} catch (Throwable e) { }
return res;
}

进入DubboProtocol中的ExchangeHandlerAdapter的replay方法:

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public Object reply(ExchangeChannel channel, Object message) throws RemotingException {
if (message instanceof Invocation) {
//Invocation中保存着方法名等
Invocation inv = (Invocation) message;
//获取Invoker
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){
return null;
}
}
RpcContext.getContext().setRemoteAddress(channel.getRemoteAddress());
//执行调用,然后返回结果
return invoker.invoke(inv);
}
throw new RemotingException(。。。);
}

先看下getInvoker获取Invoker:

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Invoker<?> getInvoker(Channel channel, Invocation inv) throws RemotingException{
boolean isCallBackServiceInvoke = false;
boolean isStubServiceInvoke = false;
int port = channel.getLocalAddress().getPort();
String path = inv.getAttachments().get(Constants.PATH_KEY);
//如果是客户端的回调服务.
isStubServiceInvoke = Boolean.TRUE.toString().equals(inv.getAttachments().get(Constants.STUB_EVENT_KEY));
if (isStubServiceInvoke){
port = channel.getRemoteAddress().getPort();
}
//callback
isCallBackServiceInvoke = isClientSide(channel) && !isStubServiceInvoke;
if(isCallBackServiceInvoke){
path = inv.getAttachments().get(Constants.PATH_KEY)+"."+inv.getAttachments().get(Constants.CALLBACK_SERVICE_KEY);
inv.getAttachments().put(IS_CALLBACK_SERVICE_INVOKE, Boolean.TRUE.toString());
}
String serviceKey = serviceKey(port, path, inv.getAttachments().get(Constants.VERSION_KEY), inv.getAttachments().get(Constants.GROUP_KEY));
//从之前缓存的exporterMap中查找Exporter
//key:dubbo.common.hello.service.HelloService:20880
DubboExporter<?> exporter = (DubboExporter<?>) exporterMap.get(serviceKey);

if (exporter == null)
throw new RemotingException(。。。);
//得到Invoker,返回
return exporter.getInvoker();
}

再看执行调用invoker.invoke(inv);,会先进入InvokerWrapper:

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public Result invoke(Invocation invocation) throws RpcException {
return invoker.invoke(invocation);
}

接着进入AbstractProxyInvoker:

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public Result invoke(Invocation invocation) throws RpcException {
try {
//先doInvoke
//然后封装成结果返回
return new RpcResult(doInvoke(proxy, invocation.getMethodName(), invocation.getParameterTypes(), invocation.getArguments()));
} catch (InvocationTargetException e) {。。。}
}

这里的doInvoke是在JavassistProxyFactory中的AbstractProxyInvoker实例:

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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 {
//这里就调用了具体的方法
return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments);
}
};
}

消息处理完后返回到HeaderExchangeHandler的received方法:

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public void received(Channel channel, Object message) throws RemotingException {
channel.setAttribute(KEY_READ_TIMESTAMP, System.currentTimeMillis());
ExchangeChannel exchangeChannel = HeaderExchangeChannel.getOrAddChannel(channel);
try {
//request类型的消息
if (message instanceof Request) {
Request request = (Request) message;
if (request.isEvent()) {//判断心跳还是正常请求
// 处理心跳
handlerEvent(channel, request);
} else {//正常的请求
//需要返回
if (request.isTwoWay()) {
//处理请求,并构造响应信息,这在上面已经解析过了
Response response = handleRequest(exchangeChannel, request);
//NettyChannel,发送响应信息
channel.send(response);
} else {//不需要返回的处理
handler.received(exchangeChannel, request.getData());
}
}
} else if (message instanceof Response) {//response类型的消息
handleResponse(channel, (Response) message);
} else if (message instanceof String) {
if (isClientSide(channel)) {
Exception e = new Exception("Dubbo client can not supported string message: " + message + " in channel: " + channel + ", url: " + channel.getUrl());
} else {//telnet类型
String echo = handler.telnet(channel, (String) message);
if (echo != null && echo.length() > 0) {
channel.send(echo);
}
}
} else {
handler.received(exchangeChannel, message);
}
} finally {
HeaderExchangeChannel.removeChannelIfDisconnected(channel);
}
}

解析完请求,构造完响应消息,就开始发送响应了,channel.send(response);,先经过AbstractPeer:

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public void send(Object message) throws RemotingException {
//NettyChannel
send(message, url.getParameter(Constants.SENT_KEY, false));
}

进入NettyChannel中,进行响应消息的发送:

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public void send(Object message, boolean sent) throws RemotingException {
//AbstractChannel的处理
super.send(message, sent);

boolean success = true;
int timeout = 0;
try {
ChannelFuture future = channel.write(message);
if (sent) {
timeout = getUrl().getPositiveParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
success = future.await(timeout);
}
Throwable cause = future.getCause();
if (cause != null) {
throw cause;
}
} catch (Throwable e) {
throw new RemotingException(this, "Failed to send message " + message + " to " + getRemoteAddress() + ", cause: " + e.getMessage(), e);
}

if(! success) {
throw new RemotingException(this, "Failed to send message " + message + " to " + getRemoteAddress()
+ "in timeout(" + timeout + "ms) limit");
}
}

消费者接受到服务端返回的响应后的处理

服务提供者端接收到消费者端的请求并处理之后,返回给消费者端,消费者这边接受响应的入口跟提供者差不多,也是NettyCodecAdapter.messageReceived(),经过解码,到NettyHandler.messageReceived()处理:

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public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
try {
//NettyClient
handler.received(channel, e.getMessage());
} finally {
NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
}
}

先经过AbstractPeer的received方法:

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public void received(Channel ch, Object msg) throws RemotingException {
if (closed) {
return;
}
//MultiMessageHandler
handler.received(ch, msg);
}

进入MultiMessageHandler:

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public void received(Channel channel, Object message) throws RemotingException {
if (message instanceof MultiMessage) {
MultiMessage list = (MultiMessage)message;
for(Object obj : list) {
handler.received(channel, obj);
}
} else {
//HeartbeatHandler
handler.received(channel, message);
}
}

进入HeartbeatHandler,根据不同类型进行处理:

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public void received(Channel channel, Object message) throws RemotingException {
setReadTimestamp(channel);
if (isHeartbeatRequest(message)) {
Request req = (Request) message;
if (req.isTwoWay()) {
Response res = new Response(req.getId(), req.getVersion());
res.setEvent(Response.HEARTBEAT_EVENT);
channel.send(res);
if (logger.isInfoEnabled()) {
int heartbeat = channel.getUrl().getParameter(Constants.HEARTBEAT_KEY, 0);
if(logger.isDebugEnabled()) {
logger.debug("Received heartbeat from remote channel " + channel.getRemoteAddress()
+ ", cause: The channel has no data-transmission exceeds a heartbeat period"
+ (heartbeat > 0 ? ": " + heartbeat + "ms" : ""));
}
}
}
return;
}
if (isHeartbeatResponse(message)) {
if (logger.isDebugEnabled()) {
logger.debug(
new StringBuilder(32)
.append("Receive heartbeat response in thread ")
.append(Thread.currentThread().getName())
.toString());
}
return;
}
//AllChannelHandler
handler.received(channel, message);
}

进入AllChannelHandler:

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public void received(Channel channel, Object message) throws RemotingException {
ExecutorService cexecutor = getExecutorService();
try {
cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.RECEIVED, message));
} catch (Throwable t) {
throw new ExecutionException(message, channel, getClass() + " error when process received event .", t);
}
}

然后在新线程,ChannelEventRunnable的run方法中进入DecodeHandler:

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public void received(Channel channel, Object message) throws RemotingException {
if (message instanceof Decodeable) {
decode(message);
}

if (message instanceof Request) {
decode(((Request)message).getData());
}
//这里进行response类型的处理
if (message instanceof Response) {
decode( ((Response)message).getResult());
}

handler.received(channel, message);
}

进入处理response的decode方法,进行解码response:

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private void decode(Object message) {
if (message != null && message instanceof Decodeable) {
try {
((Decodeable)message).decode();
} catch (Throwable e) {。。。} // ~ end of catch
} // ~ end of if
}

接着会进入HeaderExchangerHandler.received () 方法:

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public void received(Channel channel, Object message) throws RemotingException {
channel.setAttribute(KEY_READ_TIMESTAMP, System.currentTimeMillis());
ExchangeChannel exchangeChannel = HeaderExchangeChannel.getOrAddChannel(channel);
try {
if (message instanceof Request) {
Request request = (Request) message;
if (request.isEvent()) {
handlerEvent(channel, request);
} else {
if (request.isTwoWay()) {
Response response = handleRequest(exchangeChannel, request);
channel.send(response);
} else {
handler.received(exchangeChannel, request.getData());
}
}
} else if (message instanceof Response) {
//这里处理response消息
handleResponse(channel, (Response) message);
} else if (message instanceof String) {
if (isClientSide(channel)) { Exception } else {
String echo = handler.telnet(channel, (String) message);
if (echo != null && echo.length() > 0) {
channel.send(echo);
}
}
} else {
handler.received(exchangeChannel, message);
}
} finally {
HeaderExchangeChannel.removeChannelIfDisconnected(channel);
}
}

handleResponse方法:

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static void handleResponse(Channel channel, Response response) throws RemotingException {
if (response != null && !response.isHeartbeat()) {
DefaultFuture.received(channel, response);
}
}

这一步设置response到消费者请求的Future中,以供消费者通过DefaultFuture.get()取得提供者的响应,此为同步转异步重要一步,且请求超时也由DefaultFuture控制。

然后就是return (Result) currentClient.request(inv, timeout).get();在DubboInvoker中,这里继续执行,然后执行Filter,最后返回到InvokerInvocationHandler.invoker()方法中,方法得到调用结果,结束!

注意:

消费者端的DubboInvoker发起请求后,后续的逻辑是异步的或是指定超时时间内阻塞的,直到得到响应结果后,继续执行DubboInvoker中逻辑。

对于异步请求时,消费者得到Future,其余逻辑均是异步的。

消费者还可以通过设置async、sent、return来调整处理逻辑,async指异步还是同步请求,sent指是否等待请求消息发出即阻塞等待是否成功发出请求、return指是否忽略返回值即但方向通信,一般异步时使用以减少Future对象的创建和管理成本。

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