浅谈服务调用

调用远程方法前,先获取invoker

public class InvokerInvocationHandler implements InvocationHandler {

    private final Invoker<?> invoker;

    public InvokerInvocationHandler(Invoker<?> handler) {
        this.invoker = handler;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        return invoker.invoke(new RpcInvocation(method, args)).recreate();
    }
}

在集群的情况下, 进行invoker的切换

public class MockClusterInvoker<T> implements Invoker<T> {
    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);
        }
        ...
       return result;
    }
}

根据方法名,寻找有几个可以执行的方法

public abstract class AbstractClusterInvoker<T> implements Invoker<T> {
    public Result invoke(final Invocation invocation) throws RpcException {
        checkWhetherDestroyed();
        LoadBalance loadbalance = null;
        //得到可以执行的方法
        List<Invoker<T>> invokers = list(invocation);
        //进入负载均衡机制
        if (invokers != null && !invokers.isEmpty()) {
            loadbalance = ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(invokers.get(0).getUrl()
                    .getMethodParameter(invocation.getMethodName(), Constants.LOADBALANCE_KEY, Constants.DEFAULT_LOADBALANCE));
        }
        RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
        return doInvoke(invocation, invokers, loadbalance);
    }
}

对Invoker进行操作

public class FailoverClusterInvoker<T> extends AbstractClusterInvoker<T> {

    private static final Logger logger = LoggerFactory.getLogger(FailoverClusterInvoker.class);

    public FailoverClusterInvoker(Directory<T> directory) {
        super(directory);
    }

    @Override
    @SuppressWarnings({"unchecked", "rawtypes"})
    public Result doInvoke(Invocation invocation, final List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
        
        for (int i = 0; i < len; i++) {
            ...
            //根据负载均衡选择invoker
            Invoker<T> invoker = select(loadbalance, invocation, copyinvokers, invoked);
            invoked.add(invoker);
            RpcContext.getContext().setInvokers((List) invoked);
            try{
                //进行了很多的filter调用,最后会进入DubboInvoker.class
                Result result = invoker.invoke(invocation);
            }
            ...
       }
}

得到请求的结果

public class DubboInvoker<T> extends AbstractInvoker<T> {
    ...
    //创建客户端
    ExchangeClient currentClient;
    //得到客户端,客户端在之前暴露过
    if (clients.length == 1) {
        currentClient = clients[0];
    } else {
        currentClient = clients[index.getAndIncrement() % clients.length];
    }
    ...
    return (Result) currentClient.request(inv, timeout).get();
    ...
}