dubbo_rpc包中thrift协议的使用过程

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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 <T> Invoker<T> refer( Class<T> type, URL url ) throws RpcException {        ThriftInvoker<T> invoker = new ThriftInvoker<T>(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<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 {            <span style="background-color: rgb(255, 255, 102);">return doInvoke(invocation);//由具体协议实现</span>        } 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);        }    }

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