Retrofit源码分析 （六. Retrofit 深入ParameterHandler及其他）

方法数据解析

ParameterHandler是一个抽象泛型类，子类实现对其所有的注解进行解析。

@Body，@DELETE，@Field，@FieldMap，@FormUrlEncoded，@GET,@HEAD….

ParameterHandler 主要有2个实现方法和一个抽象函数，代码如下：

abstract class ParameterHandler<T> {

   // 这个就子类实现注解解析地方。本质就是各个对应的注解值value注入到builder中...
  abstract void apply(RequestBuilder builder, T value) throws IOException;

  // 迭代器 解析
  final ParameterHandler<Iterable<T>> iterable() {
    return new ParameterHandler<Iterable<T>>() {
      @Override void apply(RequestBuilder builder, Iterable<T> values) throws IOException {
        if (values == null) return; // Skip null values.

        for (T value : values) {
          ParameterHandler.this.apply(builder, value);
        }
      }
    };
  }

   // 数组 解析
  final ParameterHandler<Object> array() {
    return new ParameterHandler<Object>() {
      @Override void apply(RequestBuilder builder, Object values) throws IOException {
        if (values == null) return; // Skip null values.

        for (int i = 0, size = Array.getLength(values); i < size; i++) {
          //noinspection unchecked
          ParameterHandler.this.apply(builder, (T) Array.get(values, i));
        }
      }
    };
  }

上面的代码好奇怪，为什么ParameterHandler里面还有iterable和array呢？

这久要从严谨的代码开始说起了。

因为在retrofit2.ServiceMethod.Builder$Builder里ServiceMethod.build()时候会

ParameterHandler

我们还是要从头看代码，简单一步步深入理解哦。

retrofit2.Retrofit#create中的代理实现。

        ServiceMethod<Object, Object> serviceMethod =
            (ServiceMethod<Object, Object>) loadServiceMethod(method);

        // args 是我们例子Interface中方法的参数。
        // serviceMethod 是方法里面的缓存呀，注解解析数据值eeg.....
        // OkHttpCall则是利用okhttp3封装的请求，
        OkHttpCall<Object> okHttpCall = new OkHttpCall<>(serviceMethod, args);
        // adapt相当于一个请求是配置,可外置builder.addCallAdapterFactory()，例如与Rxjava结合使用。
        // 
        serviceMethod.callAdapter.adapt(okHttpCall);

retrofit2.Retrofit.Builder#build 创建一些初始数据。

public Retrofit build() {

  okhttp3.Call.Factory callFactory = this.callFactory;
   // 如果callFactory未初始化HttpClient，则默认创建调用OkHttpClient。
   // 也就是默认了okhttp3为Retrofit网络请求工具。 
  if (callFactory == null) {
    callFactory = new OkHttpClient();
  }

  Executor callbackExecutor = this.callbackExecutor;
    // 如果callbackExecutor 则调platform类提供的默认线程方法
  if (callbackExecutor == null) {
    callbackExecutor = platform.defaultCallbackExecutor();
  }

  // Make a defensive copy of the adapters and add the default Call adapter.
  List<CallAdapter.Factory> adapterFactories = new ArrayList<>(this.adapterFactories);
  adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));

  // Make a defensive copy of the converters.
  List<Converter.Factory> converterFactories = new ArrayList<>(this.converterFactories);

    adapterFactories和converterFactories是一个List，则说明是可有自由的扩展性
    例如：Converter.Factory可JSON，可String，可XML eg...

  return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
      callbackExecutor, validateEagerly);
}

public Builder client(OkHttpClient client) {
return callFactory(checkNotNull(client, “client == null”));
}

/**
 * Specify a custom call factory for creating {@link Call} instances.
 * <p>
 * Note: Calling {@link #client} automatically sets this value.
 */
public Builder callFactory(okhttp3.Call.Factory factory) {
  this.callFactory = checkNotNull(factory, "factory == null");
  return this;
}

这个默认的实现是okhttp3.Call.Factory，其实就是retrofit2.RequestBuilder组装okhttp3.Call.Factory的Request

也是默认关联OKhttp，处理请求

retrofit2.ExecutorCallAdapterFactory是一个子实现类retrofit2.CallAdapter.Factory。

处理请求失败或者成功。



retrofit2.ExecutorCallAdapterFactory.ExecutorCallbackCall#execute

final Executor callbackExecutor;
final Call<T> delegate;

// 从retrofit2.Call#execute间接调用okhttp3.Call#execute，发起网络请求。
@Override public Response<T> execute() throws IOException {
  return delegate.execute();
}

retrofit2.OkHttpCall#request之后，通过retrofit2.Callback回调结果。下面将retrofit2.OkHttpCall部分源码

retrofit2.Callback 就2个回调，要不失败，要不成功。

// 将Retrofit里retrofit2.Call 转为 okhttp3.Call。
private okhttp3.Call createRawCall() throws IOException {
Request request = serviceMethod.toRequest(args); //传递方法参数
// request 转实际 okhttp3.Call
okhttp3.Call call = serviceMethod.callFactory.newCall(request);
if (call == null) {
throw new NullPointerException(“Call.Factory returned null.”);
}
return call;
}

parseResponse( okhttp3.Call.execute())//网络请求核心代码

// 解析okhttp3.Response参数。
Response parseResponse(okhttp3.Response rawResponse) throws IOException {
ResponseBody rawBody = rawResponse.body();

// Remove the body's source (the only stateful object) so we can pass the response along.
// 删除body资源（唯一的有状态对象），这样我们就可以传递响应了。
rawResponse = rawResponse.newBuilder()
    .body(new NoContentResponseBody(rawBody.contentType(), rawBody.contentLength()))
    .build();

int code = rawResponse.code();
if (code < 200 || code >= 300) {
  try {
    // Buffer the entire body to avoid future I/O.
    ResponseBody bufferedBody = Utils.buffer(rawBody);
    return Response.error(bufferedBody, rawResponse);
  } finally {
    rawBody.close();
  }
}

if (code == 204 || code == 205) {
  rawBody.close();
  return Response.success(null, rawResponse);
}

ExceptionCatchingRequestBody catchingBody = new ExceptionCatchingRequestBody(rawBody);
try {
  // 类型转换，将Response的结果转为对象。
  T body = serviceMethod.toResponse(catchingBody);
  return Response.success(body, rawResponse);
} catch (RuntimeException e) {
  // If the underlying source threw an exception, propagate that rather than indicating it was
  // a runtime exception.
  catchingBody.throwIfCaught();
  throw e;
}

}

 T body = serviceMethod.toResponse(catchingBody);到底是什么呢？我们来追踪一下。

retrofit2.ServiceMethod#toResponse 上面的T即是toResponse返回的值R, 实现如下：

R toResponse(ResponseBody body) throws IOException {
return responseConverter.convert(body);
}

继续追踪  
private final Converter<ResponseBody, R> responseConverter;

responseConverter是一个Converter（转换器），就是将ResponseBody转为所需要的R。

responseConverter是通过retrofit2.ServiceMethod.Builder实例化赋值的。


retrofit2.ServiceMethod.Builder#responseConverter是通过

responseConverter = createResponseConverter();

private Converter<ResponseBody, T> createResponseConverter() {
   // 获取方法的注解
  Annotation[] annotations = method.getAnnotations();
  try {
    // responseType 是在ServiceMethod.Builder的时候反射出来的
    return retrofit.responseBodyConverter(responseType, annotations);
  } catch (RuntimeException e) { // Wide exception range because factories are user code.
    throw methodError(e, "Unable to create converter for %s", responseType);
  }
}

retrofit2.Retrofit#responseBodyConverter

  public <T> Converter<ResponseBody, T> responseBodyConverter(Type type, Annotation[] annotations) {
    return nextResponseBodyConverter(null, type, annotations);
  }


 public <T> Converter<ResponseBody, T> nextResponseBodyConverter(Converter.Factory skipPast,
      Type type, Annotation[] annotations) {
    checkNotNull(type, "type == null");
    checkNotNull(annotations, "annotations == null");

    int start = converterFactories.indexOf(skipPast) + 1;
    for (int i = start, count = converterFactories.size(); i < count; i++) {

       // retrofit2.Converter.Factory#responseBodyConverter
       // 想自定义转化器的时候，需要实现上面的方法。
       // 可在retrofit2 通过addCallAdapterFactory去。.....


      Converter<ResponseBody, ?> converter =
          converterFactories.get(i).responseBodyConverter(type, annotations, this);
      if (converter != null) {
        //noinspection unchecked
        return (Converter<ResponseBody, T>) converter;
      }
    }
      //  如果执行到这来，则说明转化器写 的有bug。
    StringBuilder builder = new StringBuilder("Could not locate ResponseBody converter for ")
        .append(type)
        .append(".\n");
    if (skipPast != null) {
      builder.append("  Skipped:");
      for (int i = 0; i < start; i++) {
        builder.append("\n   * ").append(converterFactories.get(i).getClass().getName());
      }
      builder.append('\n');
    }
    builder.append("  Tried:");
    for (int i = start, count = converterFactories.size(); i < count; i++) {
      builder.append("\n   * ").append(converterFactories.get(i).getClass().getName());
    }
    throw new IllegalArgumentException(builder.toString());
  }

retrofit2.Converter是retrofit2提供的一个返回结果转化器，我们可以自定义实现此类。主要是2个方法实现。

有Type，有okhttp3.RequestBody，就可以得到我们想得到的任何类型数据。

至此，全部介绍完成，有点说的不是很明确地方，可留言，我修正。