ribbon源码之客户端

　　客户端模块的核心功能是提供统一的用户请求操作接口。

接口定义

　　客户端模块的核心是IClient接口，定义了客户端网络请求的方法。

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

　　ClientRequest为客户端定义的请求体，存储了请求uri、loadbalancer的key，是否重试、配置。

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

　　IResponse为客户端定义的响应内容的接口。

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

　　IClientConfigAware定义了需要使用IClientConfig初始化IClient的方法。

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

类图

客户端工厂类

　　客户端模块提供了一个客户端工厂类（ClientFactory）用于通过配置文件来创建IClient实例和负载均衡器（ILoadBalancer）实例。

public static synchronized IClient getNamedClient(String name) {//根据配置获取iclient实例，默认使用DefaultClientConfigImpl配置类。
        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);//实例化配置类
    return registerClientFromProperties(name, config);//通过配置文件创建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);//通过配置文件获取client的实现类
            client = (IClient<?, ?>) instantiateInstanceWithClientConfig(clientClassName, clientConfig); //通过配置文件创建client实例
            boolean initializeNFLoadBalancer = Boolean.parseBoolean(clientConfig.getProperty(
                    CommonClientConfigKey.InitializeNFLoadBalancer, DefaultClientConfigImpl.DEFAULT_ENABLE_LOADBALANCER).toString());
            if (initializeNFLoadBalancer) {//如果需要初始化负载均衡器，则通过配置文件创建一个负载均衡器
                loadBalancer  = registerNamedLoadBalancerFromclientConfig(restClientName, clientConfig);
            }
            if (client instanceof AbstractLoadBalancerAwareClient) {//如果client实现AbstractLoadBalancerAwareClient，则注入负载均衡器
                ((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类
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实现了IClientConfigAware，ClientFactory在创建时会使用IClientConfig进行初始化。
          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();
   }

　　使用客户端工厂类（ClientFactory）涉及的配置：

属性	实现	默认值
clientname.ribbon.ClientClassName	client使用的IClient实现类	com.netflix.niws.client.http.RestClient
clientname.ribbon.InitializeNFLoadBalancer	是否初始化负载均衡器	true
clientname.ribbon.NFLoadBalancerClassName	负载均衡器的实现类	com.netflix.loadbalancer.ZoneAwareLoadBalancer

类图

客户端实现类

　　AbstractLoadBalancerAwareClient实现了通过负载均衡器进行请求调用。LoadBalancerCommand对负载均衡器操作进行了模版，对请求调用提供了回调函数。

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);//设置最终的调用uri。
                        try {
                            return Observable.just(AbstractLoadBalancerAwareClient.this.execute(requestForServer, requestConfig));
                        } //调用execute方法执行请求调用。
                        catch (Exception e) {
                            return Observable.error(e);
                        }
                    }
                })
                .toBlocking()
                .single();
        ...
        
    }

　　LoadBalancerCommand调用了负载均衡器获得了一个server，然后调用回调函数执行请求。此外还提供了各个关键节点的监听器和异常重试机制。

public Observable<T> submit(final ServerOperation<T> operation) {
        final ExecutionInfoContext context = new ExecutionInfoContext();
        if (listenerInvoker != null) {//执行回调接口
            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))//调用负载均衡器获得目标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);
                }
            }
        });
    }

　　子类 HttpRequest用于http请求，内部定义了http请求的各个内容，并且使用了builder模式。

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

　　 

类图