dubbo源码解析(三) DubboInvoker

上篇dubbo源码解析(二)中说到创建代理时会通过refprotocol.refer(interfaceClass, urls.get(0))先创建一个invoker对象出来

以DubboProtocol为例

public <T> Invoker<T> refer(Class<T> serviceType, URL url) throws RpcException {
        // create rpc invoker.
        DubboInvoker<T> invoker = new DubboInvoker<T>(serviceType, url, getClients(url), invokers);
        invokers.add(invoker);
        return invoker;
    }

执行refer时，会创建一个DubboInvoker对象返回

我们再看DubboInvoker这个类

这个类继承自AbstractInvoker，而AbstractInvoker这个类实现了Invoker接口，也就实现了，invoke方法

方法如下：

public Result invoke(Invocation inv) throws RpcException {
        if(destroyed) {
            throw new RpcException("Rpc invoker for service " + this + " on consumer " + NetUtils.getLocalHost() 
                                            + " use dubbo version " + Version.getVersion()
                                            + " is DESTROYED, can not be invoked any more!");
        }
        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());
        }
        RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
        
        
        try {
            return doInvoke(invocation);
        } catch (InvocationTargetException e) { // biz exception
            Throwable te = e.getTargetException();
            if (te == null) {
                return new RpcResult(e);
            } else {
                if (te instanceof RpcException) {
                    ((RpcException) te).setCode(RpcException.BIZ_EXCEPTION);
                }
                return new RpcResult(te);
            }
        } catch (RpcException e) {
            if (e.isBiz()) {
                return new RpcResult(e);
            } else {
                throw e;
            }
        } catch (Throwable e) {
            return new RpcResult(e);
        }
    }

主要做了三件事

1. 做了一些初始化操作

2. 调用了抽象方法 doInvoke(由子类实现)

3. 捕获了 doInvoke方法的异常，将结果返回

我们接着看一下DubboInvoker的doInvoke方法

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;
        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);
                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);
        }
    }

判断与远程交互的客户端，如果是一个，直接用，如果是多个则轮训

判断接口是单方向的，直接向远端发送请求send()，如果不是，则判断是不是异步的，如果是异步调用将future放到context里，如果是同步则等接口执行完之后get出结果