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。