看Retrofit源码的一点记录

前言

网络请求库，A type-safe HTTP client for Android and Java.
使用方法参照官方文档。
本篇文章想通过分析源码看一下api接口中都支持哪些返回类型。

源码

1. Retrofit.Builder

//建造者模式
public Retrofit build() {//传入的baseUrlif (baseUrl == null) {throw new IllegalStateException("Base URL required.");}//传入的OkHttpClientokhttp3.Call.Factory callFactory = this.callFactory;if (callFactory == null) {callFactory = new OkHttpClient();}//传入的callbackExecutorExecutor callbackExecutor = this.callbackExecutor;if (callbackExecutor == null) {callbackExecutor = platform.defaultCallbackExecutor();}//保护性拷贝adapters,最后加入默认的callAdapterFactories。List<CallAdapter.Factory> callAdapterFactories = new ArrayList<>(this.callAdapterFactories);callAdapterFactories.addAll(platform.defaultCallAdapterFactories(callbackExecutor));//保护性拷贝converterFactoriesList<Converter.Factory> converterFactories = new ArrayList<>(1 + this.converterFactories.size() + platform.defaultConverterFactoriesSize());// 先加入BuiltInConverters，最后加入默认的converterFactories。converterFactories.add(new BuiltInConverters());converterFactories.addAll(this.converterFactories);converterFactories.addAll(platform.defaultConverterFactories());return new Retrofit(callFactory, baseUrl, unmodifiableList(converterFactories),unmodifiableList(callAdapterFactories), callbackExecutor, validateEagerly);}

2. 动态代理

public <T> T create(final Class<T> service) {Utils.validateServiceInterface(service);if (validateEagerly) {eagerlyValidateMethods(service);}return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[] { service },new InvocationHandler() {private final Platform platform = Platform.get();private final Object[] emptyArgs = new Object[0];@Override public @Nullable Object invoke(Object proxy, Method method,@Nullable 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);}return loadServiceMethod(method).invoke(args != null ? args : emptyArgs);}});
}

ServiceMethod，Coroutines

1. ServiceMethod

abstract class ServiceMethod<T> {static <T> ServiceMethod<T> parseAnnotations(Retrofit retrofit, Method method) {RequestFactory requestFactory = RequestFactory.parseAnnotations(retrofit, method);Type returnType = method.getGenericReturnType();if (Utils.hasUnresolvableType(returnType)) {throw methodError(method,"Method return type must not include a type variable or wildcard: %s", returnType);}if (returnType == void.class) {throw methodError(method, "Service methods cannot return void.");}//调用HttpServiceMethod的parseAnnotations生成ServiceMethodreturn HttpServiceMethod.parseAnnotations(retrofit, method, requestFactory);}abstract @Nullable T invoke(Object[] args);
}

2. HttpServiceMethod

   abstract class HttpServiceMethod<ResponseT, ReturnT> extends ServiceMethod<ReturnT> {static <ResponseT, ReturnT> HttpServiceMethod<ResponseT, ReturnT> parseAnnotations(Retrofit retrofit, Method method, RequestFactory requestFactory) {//前面代码省略，根据条件创建不同的ServiceMethodif (!isKotlinSuspendFunction) {//如果不是挂起函数就创建CallAdapted，使用callAdapterreturn new CallAdapted<>(requestFactory, callFactory, responseConverter, callAdapter);} else if (continuationWantsResponse) {//协程return (HttpServiceMethod<ResponseT, ReturnT>) new SuspendForResponse<>(requestFactory,callFactory, responseConverter, (CallAdapter<ResponseT, Call<ResponseT>>) callAdapter);} else {//协程return (HttpServiceMethod<ResponseT, ReturnT>) new SuspendForBody<>(requestFactory,callFactory, responseConverter, (CallAdapter<ResponseT, Call<ResponseT>>) callAdapter,continuationBodyNullable);}}//前面Retrofit动态代理调用的invoke方法在这里实现@Override final @Nullable ReturnT invoke(Object[] args) {Call<ResponseT> call = new OkHttpCall<>(requestFactory, args, callFactory, responseConverter);return adapt(call, args);}protected abstract @Nullable ReturnT adapt(Call<ResponseT> call, Object[] args);
   }
   

3. CallAdapted

   final class CallAdapted<ResponseT, ReturnT> extends HttpServiceMethod<ResponseT, ReturnT> {//通过Call完成网络请求，再用前面传入的callAdapter将结果转换为需要的类型@Override protected ReturnT adapt(Call<ResponseT> call, Object[] args) {return callAdapter.adapt(call);}
   }
   

4. SuspendForResponse，用于method是挂起函数且返回类型是Response的情况

   final class SuspendForResponse<ResponseT> extends HttpServiceMethod<ResponseT, Object> {@Override protected Object adapt(Call<ResponseT> call, Object[] args) {call = callAdapter.adapt(call);//挂起函数会自动在参数列表最后加入Continuation，这时候把这个continuation取出来Continuation<Response<ResponseT>> continuation =(Continuation<Response<ResponseT>>) args[args.length - 1];// See SuspendForBody for explanation about this try/catch.try {return KotlinExtensions.awaitResponse(call, continuation);} catch (Exception e) {return KotlinExtensions.yieldAndThrow(e, continuation);}}
   }
   

   协程部分用到了suspendCancellableCoroutine，Call和Response是OkHttp对应类的封装，本质上还是调用call.enqueue，结果通过continuation回调返回

   suspend fun <T : Any> Call<T>.awaitResponse(): Response<T> {return suspendCancellableCoroutine { continuation ->continuation.invokeOnCancellation {cancel()}enqueue(object : Callback<T> {override fun onResponse(call: Call<T>, response: Response<T>) {continuation.resume(response)}override fun onFailure(call: Call<T>, t: Throwable) {continuation.resumeWithException(t)}})}
   }
   

5. SuspendForBody(部分代码)，用于method是挂起函数且返回类型是ResponseT的情况，就是converter转换的对象类型

   final class SuspendForBody<ResponseT> extends HttpServiceMethod<ResponseT, Object> {private final boolean isNullable;@Override protected Object adapt(Call<ResponseT> call, Object[] args) {call = callAdapter.adapt(call);//挂起函数会自动在参数列表最后加入Continuation，这时候把这个continuation取出来Continuation<ResponseT> continuation = (Continuation<ResponseT>) args[args.length - 1];//分为返回类型是否可为空，KotlinExtensions.await会在返回对象为空时抛出异常try {return isNullable? KotlinExtensions.awaitNullable(call, continuation): KotlinExtensions.await(call, continuation);} catch (Exception e) {return KotlinExtensions.yieldAndThrow(e, continuation);}}
   }
   

   @JvmName("awaitNullable")
   suspend fun <T : Any> Call<T?>.await(): T? {return suspendCancellableCoroutine { continuation ->continuation.invokeOnCancellation {cancel()}enqueue(object : Callback<T?> {override fun onResponse(call: Call<T?>, response: Response<T?>) {if (response.isSuccessful) {continuation.resume(response.body())} else {continuation.resumeWithException(HttpException(response))}}override fun onFailure(call: Call<T?>, t: Throwable) {continuation.resumeWithException(t)}})}
   }
   

CallAdapter

1. CallAdapter.Factory

    abstract class Factory {/*** 通过动态代理的method返回类型来返回一个CallAdapter，如果factory不能处理则返回null*/public abstract @Nullable CallAdapter<?, ?> get(Type returnType, Annotation[] annotations,Retrofit retrofit);/*** 通过index和type取出泛型参数的上届通配符。* 例如：Map，index为1时返回Runnable.*/protected static Type getParameterUpperBound(int index, ParameterizedType type) {return Utils.getParameterUpperBound(index, type);}/*** 通过type取出原始类型。例如：List返回List.class*/protected static Class<?> getRawType(Type type) {return Utils.getRawType(type);}}
   

2. DefaultCallAdapterfFactory

   • 有2种默认的CallAdapterfFactory：DefaultCallAdapterfFactory和CompletableFutureCallAdapterFactory都继承自CallAdapter.Factory
   • CallAdapterfFactory的集合会先加入通过addCallAdapterFactory加入的factory，最后默认都会加入DefaultCallAdapterfFactory，Platform会判断api>=24时加入CompletableFutureCallAdapterFactory（单例饿汉）
   • DefaultCallAdapterfFactory会处理method返回类型为Call的情况，ExecutorCallbackCall实现Call接口（装饰器模式）目的是call.enqueue的回调切到主线程执行（使用MainThreadExecutor切换线程）。
   • CompletableFutureCallAdapterFactory会处理method返回类型为CompletableFuture的情况，T是Converter转换的类型或是Response
   • 综上默认的CallAdapterfFactory支持method返回类型为Call和CompletableFuture，其余的返回类型需要传入的CallAdapterfFactory支持，如RxJava2CallAdapterFactory

3. CallAdapter（适配器模式）

   public interface CallAdapter<R, T> {/*** 返回的对象类型*/Type responseType();/*** 返回的对象*/T adapt(Call<R> call);
   }
   

Converter

1. Converter.Factory

   abstract class Factory {/*** 返回一个converter用于转换HTTP ResponseBody到type类型，如果不能处理则返回null。* 例如从Call转换为类型SimpleResponse。*/public @Nullable Converter<ResponseBody, ?> responseBodyConverter(Type type,Annotation[] annotations, Retrofit retrofit) {return null;}/*** 返回一个converter用于转换type类型到HTTP RequestBody，如果不能处理则返回null。* 通常用于@Body，@Part，@PartMap注解的type。*/public @Nullable Converter<?, RequestBody> requestBodyConverter(Type type,Annotation[] parameterAnnotations, Annotation[] methodAnnotations, Retrofit retrofit) {return null;}/*** 返回一个converter用于转换type类型到String，如果不能处理则返回null。* 通常用于@Field，@FieldMap，@Header,@HeaderMap,@Path,@Query,@QueryMap注解的type。 */public @Nullable Converter<?, String> stringConverter(Type type, Annotation[] annotations,Retrofit retrofit) {return null;}/*** 通过index和type取出泛型参数的上届通配符..* 例如：Map，index为1时返回Runnable.*/protected static Type getParameterUpperBound(int index, ParameterizedType type) {return Utils.getParameterUpperBound(index, type);}/*** 通过type取出原始类型。例如：List返回List.class*/protected static Class<?> getRawType(Type type) {return Utils.getRawType(type);}}
   

2. BuiltInConverters：请求时RequestBody转为RequestBody，响应时ResponseBody转为Void,Unit,ResponseBody。

3. OptionalConverterFactory：api>=24时会通过defaultConverterFactories加入，响应时会创建OptionalConverter，将ResponseBody转为Optional

4. Converter

   /*** 对象和HTTP中代表的含义相互转换，通过Converter.Factory创建。* Request创建Converter，Response创建Converter*/
   public interface Converter<F, T> {@Nullable T convert(F value) throws IOException;
   }
   

5. ToStringConverter会处理Object转为String的情况，优先级最低，会先到自定义的converterFactories查找，如没找到才会使用ToStringConverter。在RequestFactory的parseParameterAnnotation方法中使用，

   static final class ToStringConverter implements Converter<Object, String> {static final ToStringConverter INSTANCE = new ToStringConverter();@Override public String convert(Object value) {return value.toString();}
   }
   

本文来自互联网用户投稿，文章观点仅代表作者本人，不代表本站立场，不承担相关法律责任。如若转载，请注明出处。 如若内容造成侵权/违法违规/事实不符，请点击【内容举报】进行投诉反馈！