Retrofit网络请求和响应处理重点分析讲解

public <T> T execute(Call<T> call) throws IOException {
  Utils.validateServiceInterface(call.request().tag(), call.request().url().toString());
  return (T) callAdapter(call, call.request().tag()).adapt(call).execute();
}

private CallAdapter<?, ?> callAdapter(Call<?> call, Object tag) {
  Type responseType = call.request().method().equals("HEAD")
      ? Void.class
      : getParameterUpperBound(0, (ParameterizedType) call.request().tag());
  return callAdapter(tag, responseType);
}

public <R, T> CallAdapter<R, T> callAdapter(Object tag, Type returnType) {
  // ...
  for (CallAdapter.Factory factory : adapterFactories) {
    CallAdapter<?, ?> adapter = factory.get(returnType, annotations, this);
    if (adapter != null) {
      return (CallAdapter<R, T>) adapter;
    }
  }
  // ...
}

public <T> void enqueue(Call<T> call, Callback<T> callback) {
  Utils.validateServiceInterface(call.request().tag(), call.request().url().toString());
  callAdapter(call, call.request().tag()).adapt(call).enqueue(new CallbackRunnable<>(callback));
}

public void enqueue(final Callback<T> callback) {
  delegate.enqueue(new Callback<Response<T>>() {
    @Override public void onResponse(Call<Response<T>> call, Response<Response<T>> response) {
      Response<T> body;
      try {
        body = response.body();
      } catch (Throwable t) {
        if (response.code() == 204) {
          body = null;
        } else {
          callback.onFailure(call, t);
          return;
        }
      }
      if (response.isSuccessful()) {
        callback.onResponse(call, Response.success(body, response.raw()));
      } else {
        callback.onFailure(call, Response.error(response.errorBody(), response.raw()));
      }
    }
    @Override public void onFailure(Call<Response<T>> call, Throwable t) {
      callback.onFailure(call, t);
    }
  });
}

public Retrofit(Builder builder) {
  // ...
  if (builder.converterFactories == null) {
    converterFactories.add(Platform.get().defaultConverterFactory());
  } else {
    converterFactories.addAll(builder.converterFactories);
  }
  // ...
}
public interface Platform {
  // ...
  Converter.Factory defaultConverterFactory();
}

public <T> T execute(Call<T> call) throws IOException {
  // ...
  Response<T> response = call.execute();
  if (response.isSuccessful()) {
    return response.body();
  } else {
    Converter<ResponseBody, ErrorResponse> converter = retrofit.responseBodyConverter(
        ErrorResponse.class, new Annotation[0]);
    throw new ApiException(converter.convert(response.errorBody()));
  }
}
@SuppressWarnings("unchecked") // Single-interface proxy creation guarded by parameter safety.
public <T> T adapt(Call<T> call) {
  return (T) new OkHttpCall<>(requestFactory, callFactory, converter, call);
}
public <T> Converter<ResponseBody, T> responseBodyConverter(Type type, Annotation[] annotations) {
  return nextResponseBodyConverter(null, type, annotations);
}
public <T> Converter<ResponseBody, T> nextResponseBodyConverter(
    @Nullable Converter.Factory skipPast, Type type, Annotation[] annotations) {
  Objects.requireNonNull(type, "type == null");
  Objects.requireNonNull(annotations, "annotations == null");
  int start = converterFactories.indexOf(skipPast) + 1;
  for (int i = start, count = converterFactories.size(); i < count; i++) {
    Converter<ResponseBody, ?> converter =
        converterFactories.get(i).responseBodyConverter(type, annotations, this);
    if (converter != null) {
      return (Converter<ResponseBody, T>) converter;
    }
  }
  throw new IllegalArgumentException(
      "Could not locate ResponseBody converter for " + type + " with annotations " + Arrays.toString(annotations));
}

public interface ApiService {
  @GET("users/{user}/repos")
  Call<List<Repo>> listRepos(@Path("user") String user);
}
Retrofit retrofit = new Retrofit.Builder()
    .baseUrl("https://api.github.com/")
    .addConverterFactory(GsonConverterFactory.create())
    .build();
ApiService apiService = retrofit.create(ApiService.class);
Call<List<Repo>> call = apiService.listRepos("smallmarker");
List<Repo> repos = call.execute().body();

public final class GsonConverterFactory extends Converter.Factory {
  private final Gson gson;
  private GsonConverterFactory(Gson gson) {
    this.gson = gson;
  }
  public static GsonConverterFactory create() {
    return create(new Gson());
  }
  public static GsonConverterFactory create(Gson gson) {
    if (gson == null) throw new NullPointerException("gson == null");
    return new GsonConverterFactory(gson);
  }
  @Override
  public @Nullable Converter<ResponseBody, ?> responseBodyConverter(Type type, Annotation[] annotations, Retrofit retrofit) {
    TypeAdapter<?> adapter = gson.getAdapter(TypeToken.get(type));
    return new GsonResponseBodyConverter<>(gson, adapter);
  }
  @Override
  public @Nullable Converter<?, RequestBody> requestBodyConverter(Type type, Annotation[] parameterAnnotations,
                                                                  Annotation[] methodAnnotations, Retrofit retrofit) {
    TypeAdapter<?> adapter = gson.getAdapter(TypeToken.get(type));
    return new GsonRequestBodyConverter<>(gson, adapter);
  }
}