客戶端模組的核心功能是提供統一的使用者請求操作介面。

介面定義

　　客戶端模組的核心是IClient介面，定義了客戶端網路請求的方法。

public interface IClient<S extends ClientRequest, T extends IResponse> {
    public T execute(S request, IClientConfig requestConfig) throws Exception; 
}

　　ClientRequest為客戶端定義的請求體，儲存了請求uri、loadbalancer的key，是否重試、配置。

public class ClientRequest implements Cloneable {
    protected URI uri;
    protected Object loadBalancerKey = null;
    protected Boolean isRetriable = null;
    protected IClientConfig overrideConfig;
}

　　IResponse為客戶端定義的響應內容的介面。

public interface IResponse extends Closeable
{
   public
 
 Object getPayload() throws ClientException;
   public boolean hasPayload();
   public boolean isSuccess();
   public URI getRequestedURI();
   public Map<String, ?> getHeaders();   
}

　　IClientConfigAware定義了需要使用IClientConfig初始化IClient的方法。

public interface IClientConfigAware {
    public
 
 abstract void initWithNiwsConfig(IClientConfig clientConfig);
}

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客戶端工廠類

　　客戶端模組提供了一個客戶端工廠類（ClientFactory）用於通過配置檔案來建立IClient例項和負載均衡器（ILoadBalancer）例項。

public static synchronized IClient getNamedClient(String name) {//根據配置獲取iclient例項，預設使用DefaultClientConfigImpl配置類。
        return getNamedClient(name, DefaultClientConfigImpl.class);
    }

public static synchronized IClient getNamedClient(String name, Class<? extends IClientConfig> configClass) {
   ...
        return createNamedClient(name, configClass);
   ...
}

public static synchronized IClient createNamedClient(String name, Class<? extends IClientConfig> configClass) throws ClientException {
   IClientConfig config = getNamedConfig(name, configClass);//例項化配置類
    return registerClientFromProperties(name, config);//通過配置檔案建立iclient
}

public static synchronized ILoadBalancer getNamedLoadBalancer(String name) {
   return getNamedLoadBalancer(name, DefaultClientConfigImpl.class);
}
public static synchronized ILoadBalancer getNamedLoadBalancer(String name, Class<? extends IClientConfig> configClass) {
   ...
            lb = registerNamedLoadBalancerFromProperties(name, configClass);
   ...
}

public static synchronized IClient<?, ?> registerClientFromProperties(String restClientName, IClientConfig clientConfig) throws ClientException { 
        IClient<?, ?> client = null;
        ILoadBalancer loadBalancer = null;
        ...
            String clientClassName = (String) clientConfig.getProperty(CommonClientConfigKey.ClientClassName);//通過配置檔案獲取client的實現類
            client = (IClient<?, ?>) instantiateInstanceWithClientConfig(clientClassName, clientConfig); //通過配置檔案建立client例項
            boolean initializeNFLoadBalancer = Boolean.parseBoolean(clientConfig.getProperty(
                    CommonClientConfigKey.InitializeNFLoadBalancer, DefaultClientConfigImpl.DEFAULT_ENABLE_LOADBALANCER).toString());
            if (initializeNFLoadBalancer) {//如果需要初始化負載均衡器，則通過配置檔案建立一個負載均衡器
                loadBalancer  = registerNamedLoadBalancerFromclientConfig(restClientName, clientConfig);
            }
            if (client instanceof AbstractLoadBalancerAwareClient) {//如果client實現AbstractLoadBalancerAwareClient，則注入負載均衡器
                ((AbstractLoadBalancerAwareClient) client).setLoadBalancer(loadBalancer);
            }
        ...return client;
    }

public static ILoadBalancer registerNamedLoadBalancerFromclientConfig(String name, IClientConfig clientConfig) throws ClientException {
   ...
   ILoadBalancer lb = null;
   ...
        String loadBalancerClassName = (String) clientConfig.getProperty(CommonClientConfigKey.NFLoadBalancerClassName);//
        lb = (ILoadBalancer) ClientFactory.instantiateInstanceWithClientConfig(loadBalancerClassName, clientConfig);                                    
        ...
        return lb;
   ...      
}
//初始化指定的class類
public static Object instantiateInstanceWithClientConfig(String className, IClientConfig clientConfig) 

          throws InstantiationException, IllegalAccessException, ClassNotFoundException {
       Class clazz = Class.forName(className);
       if (IClientConfigAware.class.isAssignableFrom(clazz)) {//如果指定的iclient實現了IClientConfigAware，ClientFactory在建立時會使用IClientConfig進行初始化。
          IClientConfigAware obj = (IClientConfigAware) clazz.newInstance();
          obj.initWithNiwsConfig(clientConfig);
          return obj;
       } else {
          try {
              if (clazz.getConstructor(IClientConfig.class) != null) {
                 return clazz.getConstructor(IClientConfig.class).newInstance(clientConfig);
              }
          } catch (Throwable e) { // NOPMD             
          }         
       }
       return clazz.newInstance();
   }

　　使用客戶端工廠類（ClientFactory）涉及的配置：

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客戶端實現類

　　AbstractLoadBalancerAwareClient實現了通過負載均衡器進行請求呼叫。LoadBalancerCommand對負載均衡器操作進行了模版，對請求呼叫提供了回撥函式。

public T executeWithLoadBalancer(final S request, final IClientConfig requestConfig) throws ClientException {
        LoadBalancerCommand<T> command = buildLoadBalancerCommand(request, requestConfig);
　　　　 ...return command.submit(
                new ServerOperation<T>() {
                    @Override
                    public Observable<T> call(Server server) {
                        URI finalUri = reconstructURIWithServer(server, request.getUri());
                        S requestForServer = (S) request.replaceUri(finalUri);//設定最終的呼叫uri。
                        try {
                            return Observable.just(AbstractLoadBalancerAwareClient.this.execute(requestForServer, requestConfig));
                        } //呼叫execute方法執行請求呼叫。
                        catch (Exception e) {
                            return Observable.error(e);
                        }
                    }
                })
                .toBlocking()
                .single();
        ...
        
    }

　　LoadBalancerCommand呼叫了負載均衡器獲得了一個server，然後呼叫回撥函式執行請求。此外還提供了各個關鍵節點的監聽器和異常重試機制。

public Observable<T> submit(final ServerOperation<T> operation) {
        final ExecutionInfoContext context = new ExecutionInfoContext();
        if (listenerInvoker != null) {//執行回撥介面
            try {
                listenerInvoker.onExecutionStart();
            } catch (AbortExecutionException e) {
                return Observable.error(e);
            }
        }
        final int maxRetrysSame = retryHandler.getMaxRetriesOnSameServer();
        final int maxRetrysNext = retryHandler.getMaxRetriesOnNextServer();
        Observable<T> o = 
                (server == null ? selectServer() : Observable.just(server))//呼叫負載均衡器獲得目標server
                .concatMap(new Func1<Server, Observable<T>>() {
                    ...return operation.call(server).doOnEach(new Observer<T>() {
                                            ....
                                        });
                    ...
                        if (maxRetrysSame > 0) 
                            o = o.retry(retryPolicy(maxRetrysSame, true));
                        return o;
                    }
                });
            
        if (maxRetrysNext > 0 && server == null) 
            o = o.retry(retryPolicy(maxRetrysNext, false));
        
        return o.onErrorResumeNext(new Func1<Throwable, Observable<T>>() {
            @Override
            public Observable<T> call(Throwable e) {
                if (context.getAttemptCount() > 0) {
                    if (maxRetrysNext > 0 && context.getServerAttemptCount() == (maxRetrysNext + 1)) {
                        e = new ClientException(ClientException.ErrorType.NUMBEROF_RETRIES_NEXTSERVER_EXCEEDED,
                                "Number of retries on next server exceeded max " + maxRetrysNext
                                + " retries, while making a call for: " + context.getServer(), e);
                    }
                    else if (maxRetrysSame > 0 && context.getAttemptCount() == (maxRetrysSame + 1)) {
                        e = new ClientException(ClientException.ErrorType.NUMBEROF_RETRIES_EXEEDED,
                                "Number of retries exceeded max " + maxRetrysSame
                                + " retries, while making a call for: " + context.getServer(), e);
                    }
                }
                if (listenerInvoker != null) {
                    listenerInvoker.onExecutionFailed(e, context.toFinalExecutionInfo());
                }
                return Observable.error(e);
            }
        });
    }

private Observable<Server> selectServer() {
        return Observable.create(new OnSubscribe<Server>() {
            @Override
            public void call(Subscriber<? super Server> next) {
                try {
                    Server server = loadBalancerContext.getServerFromLoadBalancer(loadBalancerURI, loadBalancerKey);   
                    next.onNext(server);
                    next.onCompleted();
                } catch (Exception e) {
                    next.onError(e);
                }
            }
        });
    }

　　子類 HttpRequest用於http請求，內部定義了http請求的各個內容，並且使用了builder模式。

public class HttpRequest extends ClientRequest {protected CaseInsensitiveMultiMap httpHeaders = new CaseInsensitiveMultiMap();//head引數
    protected Multimap<String, String> queryParams = ArrayListMultimap.create();//query引數
    private Object entity;／／訊息體
    protected Verb verb;//http請求的method：post get head delete等。預設get }

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