Retrofit

Retrofit 底层请求操作用的就是OKHttp，retrofit知识对OKHttp进行了一层的封装

大体的流程：

Retrofit 通过 java 接口以及注解来描述网络请求，并用动态代理的方式生成网络请求的 request，然后通过 client 调用相应的网络框架（默认 okhttp）去发起网络请求，并将返回的 response 通过 converterFactorty 转换成相应的数据 model，最后通过 calladapter 转换成其他数据方式（如 rxjava Observable）

OkHttpClient.Builder httpClient = new OkHttpClient.Builder();

Retrofit.Builder builder =  
    new Retrofit.Builder()
            .baseUrl(API_BASE_URL)
            .addConverterFactory(
                GsonConverterFactory.create()
            );

Retrofit retrofit =  
    builder
        .client(
            httpClient.build()
        )
        .build();

GitHubClient client =  retrofit.create(GitHubClient.class);  

client.execute()同步请求client.enqueue()异步请求

retrofit.create(GitHubClient.class);  这里使用了动态代理，具体实现如下

public <T> T create(final Class<T> service) {//检查是不是接口  Utils.validateServiceInterface(service);  if (validateEagerly) {//检查方法    eagerlyValidateMethods(service);  }//创建动态代理对象  return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[] { service },      new InvocationHandler() {        private final Platform platform = Platform.get();        @Override public Object invoke(Object proxy, Method method, Object[] args)            throws Throwable {          // If the method is a method from Object then defer to normal invocation.          if (method.getDeclaringClass() == Object.class) {            return method.invoke(this, args);          }          if (platform.isDefaultMethod(method)) {            return platform.invokeDefaultMethod(method, service, proxy, args);          }//添加接口请求方法到缓存中          ServiceMethod<Object, Object> serviceMethod =              (ServiceMethod<Object, Object>) loadServiceMethod(method);          OkHttpCall<Object> okHttpCall = new OkHttpCall<>(serviceMethod, args);          return serviceMethod.callAdapter.adapt(okHttpCall);        }      });}