dubbo_rpc包中thrift协议的使用过程



今天学习的是rpc包中的thrift协议的使用过程，以下是简单的调用步骤，在这里记录一下并做了点简单的说明。

1、首先初始化Protocol类

Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getExtension( ThriftProtocol.NAME );

2、以服务的接口类和URL为参数，调用protocol的refer()方法，返回一个具体协议的Invoker对象，此处以thrift举例，故返回ThriftInvoker对象实例；

    public  Invoker refer( Class type, URL url ) throws RpcException {

        ThriftInvoker invoker = new ThriftInvoker(type, url, getClients(url), invokers);

        invokers.add(invoker);

        return invoker;

    }

3、RpcInvocation类继承自Invocation类，主要是对回调方法的一些方法名、参数及类型等一些参数的设置，然后作为以上invoker对象调用invoke方法时的参数，来返回结果。

        RpcInvocation invocation = new RpcInvocation();

        invocation.setMethodName( "echoString" );

        invocation.setParameterTypes( new Class[]{ String.class } );

        String arg = "Hello, World!";

        invocation.setArguments( new Object[] { arg } );

        Result result = invoker.invoke( invocation );

4、invoke方法是在AbstractInvoker抽象类中进行了实现，主要还是对RpcInvocation的一些参数进行设置，具体的回调操作doInvoke（invocation）由具体协议实现

    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 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);//由具体协议实现
        } 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);
        }
    }

5、在doInvoker（）中主要是随机选择一个ExchangeClient对象进行异步回调，得到相应的结果。

    protected Result doInvoke( Invocation invocation ) throws Throwable {

        RpcInvocation inv = (RpcInvocation) invocation;

        final String methodName;

        methodName = invocation.getMethodName();

        inv.setAttachment( Constants.PATH_KEY, getUrl().getPath() );

        // for thrift codec
        inv.setAttachment( ThriftCodec.PARAMETER_CLASS_NAME_GENERATOR, getUrl().getParameter(
                ThriftCodec.PARAMETER_CLASS_NAME_GENERATOR, DubboClassNameGenerator.NAME ) );

        ExchangeClient currentClient;

        if (clients.length == 1) {
            currentClient = clients[0];
        } else {
            currentClient = clients[index.getAndIncrement() % clients.length];//随机选择一个Client
        }

        try {
            int timeout = getUrl().getMethodParameter(
                    methodName, Constants.TIMEOUT_KEY,Constants.DEFAULT_TIMEOUT);

            RpcContext.getContext().setFuture(null);

            return (Result) currentClient.request(inv, timeout).get();//进行方法异步回调

        } catch (TimeoutException e) {
            throw new RpcException(RpcException.TIMEOUT_EXCEPTION, e.getMessage(), e);
        } catch (RemotingException e) {
            throw new RpcException(RpcException.NETWORK_EXCEPTION, e.getMessage(), e);
        }

    }