Retrofit 1.9源码学习

Retrofit的建立是通过建造者模式，可以自己设置组件，比如Log，Json转换器等，如果不设置，就用默认的。

@OverrideClient.ProviderdefaultClient() {
  finalClient client;
  if (hasOkHttpOnClasspath()) {
    client = OkClientInstantiator.instantiate();
  }else if(Build.VERSION.SDK_INT< Build.VERSION_CODES.GINGERBREAD) {
    client = new AndroidApacheClient();
  }else{
    client = new UrlConnectionClient();
  }
  return newClient.Provider() {
    @Override public Client get () {
      return client;
    }
  };
}

@OverrideExecutordefaultHttpExecutor() {
  returnExecutors.newCachedThreadPool(newThreadFactory() {
    @Override public Thread newThread (finalRunnable r) {
      return new Thread(newRunnable() {
        @Override public void run() {
          Process.setThreadPriority(THREAD_PRIORITY_BACKGROUND);
          r .run();
        }
      },RestAdapter.IDLE_THREAD_NAME);
    }
  });
}

@OverrideExecutordefaultCallbackExecutor() {
  return newMainThreadExecutor();
}

@OverrideRestAdapter.LogdefaultLog() {
  return newAndroidLog("Retrofit");

}

在这里重点介绍下

finalExecutorhttpExecutor;

finalExecutorcallbackExecutor;

httpExecuter在这里是用于网络请求的，callbackExecutor是用于向Android主线程传递消息，执行返回语句的。比如

/** Executor that runs tasks on Android's main thread. */
public final classMainThreadExecutorimplementsExecutor {
  private finalHandlerhandler=newHandler(Looper.getMainLooper());

  @Overridepublic voidexecute(Runnable r) {
    handler .post(r);
  }

}

到底如何执行，是在这里

Callback<?> callback = (Callback<?>) args[args.length-1];
httpExecutor.execute(newCallbackRunnable(callback,callbackExecutor,errorHandler) {
  @OverridepublicResponseWrapperobtainResponse() {
    return (ResponseWrapper) invokeRequest(interceptorTape,methodInfo,args);
  }

});

abstract classCallbackRunnable<T>implementsRunnable {
  private finalCallback<T>callback;
  private final Executor callbackExecutor;
  private final ErrorHandler errorHandler;

  CallbackRunnable(Callback<T> callback,Executor callbackExecutor,ErrorHandler errorHandler) {
    this .callback= callback;
    this.callbackExecutor= callbackExecutor;
    this.errorHandler= errorHandler;
  }

  @SuppressWarnings("unchecked")
  @Overridepublic final voidrun() {
    try {
      final ResponseWrapper wrapper = obtainResponse();
      callbackExecutor .execute(newRunnable() {
        @Override public void run() {
          callback .success((T)wrapper.responseBody,wrapper.response);
        }
      });
    } catch (RetrofitError e) {
      Throwable cause = errorHandler .handleError(e);
      final RetrofitError handled = cause == e ? e :unexpectedError(e.getUrl(),cause);
      callbackExecutor .execute(newRunnable() {
        @Override public void run() {
          callback .failure(handled);
        }
      });
    }
  }

 public abstractResponseWrapperobtainResponse();

httpExecutor先执行obtainResponse，再调用callbackExecutor，这样就能够异步请求网络数据，并在Android主线程返回，从而可以更新界面等操作了。