Kotlin 协程+Retrofit 最优雅的网络请求使用

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时间 2022-01-14 22:15:06
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Kotlin 协程+Retrofit 最优雅的网络请求使用

1.简介

Retrofit对协程的支持非常的简陋。在kotlin中使用不符合kotlin的优雅

```kotlin interface TestServer { @GET("banner/json") suspend fun banner(): ApiResponse> }

//实现并行捕获异常的网络请求 fun oldBanner(){ viewModelScope.launch { //传统模式使用retrofit需要try catch

        val bannerAsync1 = async {
            var result : ApiResponse<List<Banner>>? = null
            kotlin.runCatching {
               service.banner()
            }.onFailure {
                Log.e("banner",it.toString())
            }.onSuccess {
                result = it 
            }
            result
        }

        val bannerAsync2 = async {
            var result : ApiResponse<List<Banner>>? = null
            kotlin.runCatching {
                service.banner()
            }.onFailure {
                Log.e("banner",it.toString())
            }.onSuccess {
                result = it
            }
            result
        }

        bannerAsync1.await()
        bannerAsync2.await()
    }
}

```

一层嵌套一层，属实无法忍受。kotlin应该一行代码解决问题，才符合kotlin的优雅

使用本框架后

```kotlin interface TestServer { @GET("banner/json") suspend fun awaitBanner(): Await> }

//实现并行捕获异常的网络请求 fun parallel(){ viewModelScope.launch { val awaitBanner1 = service.awaitBanner().tryAsync(this) val awaitBanner2 = service.awaitBanner().tryAsync(this)

  //两个接口一起调用
  awaitBanner1.await()
  awaitBanner2.await()

} } ```

2.源码地址

GitHub

3.查看Retrofit源码

先看Retrofit create方法

```kotlin public T create(final Class service) { validateServiceInterface(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);
            }
            args = args != null ? args : emptyArgs;
            return platform.isDefaultMethod(method)
                ? platform.invokeDefaultMethod(method, service, proxy, args)
                : loadServiceMethod(method).invoke(args);//具体调用
          }
        });

} ```

loadServiceMethod(method).invoke(args)进入这个方法看具体调用

20220110110008.png

20220110110243.png

我们查看suspenForResponse中的adapt

```kotlin @Override protected Object adapt(Call call, Object[] args) { call = callAdapter.adapt(call);//如果用户不设置callAdapterFactory就使用DefaultCallAdapterFactory

  //noinspection unchecked Checked by reflection inside RequestFactory.
  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.suspendAndThrow(e, continuation);
  }
}

} ```

后面直接交给协程去调用call。具体的okhttp调用在DefaultCallAdapterFactory。或者用户自定义的callAdapterFactory中

因此我们这边可以自定义CallAdapterFactory在调用后不进行网络请求的访问，在用户调用具体方法时候再进行网络请求访问。

4.自定义CallAdapterFactory

Retrofit在调用后直接进行了网络请求，因此很不好操作。我们把网络请求的控制权放在我们手里，就能随意操作。

```kotlin class ApiResultCallAdapterFactory : CallAdapter.Factory() { override fun get(returnType: Type, annotations: Array, retrofit: Retrofit): CallAdapter<, >? { //检查returnType是否是Call类型的 if (getRawType(returnType) != Call::class.java) return null check(returnType is ParameterizedType) { "$returnType must be parameterized. Raw types are not supported" } //取出Call 里的T，检查是否是Await val apiResultType = getParameterUpperBound(0, returnType) // 如果不是 Await 则不由本 CallAdapter.Factory 处理 兼容正常模式 if (getRawType(apiResultType) != Await::class.java) return null check(apiResultType is ParameterizedType) { "$apiResultType must be parameterized. Raw types are not supported" }

    //取出Await<T>中的T 也就是API返回数据对应的数据类型

// val dataType = getParameterUpperBound(0, apiResultType)

    return ApiResultCallAdapter<Any>(apiResultType)
}

}

class ApiResultCallAdapter(private val type: Type) : CallAdapter>> { override fun responseType(): Type = type

override fun adapt(call: Call<T>): Call<Await<T>> {
    return ApiResultCall(call)
}

}

class ApiResultCall(private val delegate: Call) : Call> { /* * 该方法会被Retrofit处理suspend方法的代码调用，并传进来一个callback,如果你回调了callback.onResponse，那么suspend方法就会成功返回 * 如果你回调了callback.onFailure那么suspend方法就会抛异常 * * 所以我们这里的实现是回调callback.onResponse,将okhttp的call delegate / override fun enqueue(callback: Callback>) { //将okhttp call放入AwaitImpl直接返回，不做网络请求。在调用AwaitImpl的await时才真正开始网络请求 callback.onResponse([email protected], Response.success(delegate.toResponse())) } }

internal class AwaitImpl( private val call : Call, ) : Await {

override suspend fun await(): T {

    return try {
        call.await()
    } catch (t: Throwable) {
        throw t
    }
}

} ```

通过上面自定义callAdapter后，我们延迟了网络请求，在调用Retrofit后并不会请求网络，只会将网络请求所需要的call的放入await中。

kotlin @GET("banner/json") suspend fun awaitBanner(): Await<List<Banner>>

我们拿到的Await>并没有做网络请求。在这个实体类中包含了okHttp的call。

这时候我们可以定义如下方法就能捕获异常

kotlin suspend fun <T> Await<T>.tryAsync( scope: CoroutineScope, onCatch: ((Throwable) -> Unit)? = null, context: CoroutineContext = SupervisorJob(scope.coroutineContext[Job]), start: CoroutineStart = CoroutineStart.DEFAULT ): Deferred<T?> = scope.async(context, start) { try { await() } catch (e: Throwable) { onCatch?.invoke(e) null } }

同样并行捕获异常的请求，就可以通过如下方式调用，优雅简洁了很多 ```kotlin /* * 并行 async / fun parallel(){ viewModelScope.launch { val awaitBanner1 = service.awaitBanner().tryAsync(this) val awaitBanner2 = service.awaitBanner().tryAsync(this)

        //两个接口一起调用
        awaitBanner1.await()
        awaitBanner2.await()
    }
}

```

这时候我们发现网络请求成功了，解析数据失败。因为我们在数据外面套了一层await。肯定无法解析成功。

本着哪里错误解决哪里的思路，我们自定义Gson解析

5.自定义Gson解析

```kotlin class GsonConverterFactory private constructor(private var responseCz : Class<*>,var responseConverter : GsonResponseBodyConverter, private val gson: Gson) : Converter.Factory() {

override fun responseBodyConverter(
    type: Type, annotations: Array<Annotation>,
    retrofit: Retrofit
): Converter<ResponseBody, *> {
    var adapter : TypeAdapter<*>? = null
    //检查是否是Await<T>
    if (Utils.getRawType(type) == Await::class.java && type is ParameterizedType){
        //取出Await<T>中的T
        val awaitType =  Utils.getParameterUpperBound(0, type)
        if(awaitType != null){
            adapter = gson.getAdapter(TypeToken.get(ParameterizedTypeImpl[responseCz,awaitType]))
        }
    }
    //不是awiat正常解析，兼容正常模式
    if(adapter == null){
        adapter= gson.getAdapter(TypeToken.get(ParameterizedTypeImpl[responseCz,type]))
    }
    return responseConverter.init(gson, adapter!!)
}

}

class MyGsonResponseBodyConverter : GsonResponseBodyConverter() {

override fun convert(value: ResponseBody): Any {
    val jsonReader = gson.newJsonReader(value.charStream())
    val data = adapter.read(jsonReader) as ApiResponse<*>
    val t = data.data

    val listData = t as? ApiPagerResponse<*>
    if (listData != null) {
        //如果返回值值列表封装类，且是第一页并且空数据 那么给空异常 让界面显示空
        if (listData.isRefresh() && listData.isEmpty()) {
            throw ParseException(NetConstant.EMPTY_CODE, data.errorMsg)
        }
    }

    // errCode 不等于 SUCCESS_CODE，抛出异常
    if (data.errorCode != NetConstant.SUCCESS_CODE) {
        throw ParseException(data.errorCode, data.errorMsg)
    }

    return t!!
}

} ```

6.本框架使用

添加依赖

Download

groovy implementation "io.github.cnoke.ktnet:api:?"

写一个网络请求数据基类

kotlin open class ApiResponse<T>( var data: T? = null, var errorCode: String = "", var errorMsg: String = "" )

实现com.cnoke.net.factory.GsonResponseBodyConverter

```kotlin class MyGsonResponseBodyConverter : GsonResponseBodyConverter() {

override fun convert(value: ResponseBody): Any {
    val jsonReader = gson.newJsonReader(value.charStream())
    val data = adapter.read(jsonReader) as ApiResponse<*>
    val t = data.data

    val listData = t as? ApiPagerResponse<*>
    if (listData != null) {
        //如果返回值值列表封装类，且是第一页并且空数据 那么给空异常 让界面显示空
        if (listData.isRefresh() && listData.isEmpty()) {
            throw ParseException(NetConstant.EMPTY_CODE, data.errorMsg)
        }
    }

    // errCode 不等于 SUCCESS_CODE，抛出异常
    if (data.errorCode != NetConstant.SUCCESS_CODE) {
        throw ParseException(data.errorCode, data.errorMsg)
    }

    return t!!
}

} ```

进行网络请求

```kotlin interface TestServer { @GET("banner/json") suspend fun awaitBanner(): Await> }

val okHttpClient = OkHttpClient.Builder() .addInterceptor(HeadInterceptor()) .addInterceptor(LogInterceptor()) .build()

val retrofit = Retrofit.Builder() .client(okHttpClient) .baseUrl("https://www.wanandroid.com/") .addCallAdapterFactory(ApiResultCallAdapterFactory()) .addConverterFactory(GsonConverterFactory.create(ApiResponse::class.java,MyGsonResponseBodyConverter())) .build() val service: TestServer = retrofit.create(TestServer::class.java) lifecycleScope.launch { val banner = service.awaitBanner().await() } ```

异步请求同步请求，异常捕获参考如下try开头的会捕获异常，非try开头不会捕获。

```kotlin fun banner(){ lifecycleScope.launch { //单独处理异常 tryAwait会处理异常，如果异常返回空 val awaitBanner = service.awaitBanner().tryAwait() awaitBanner?.let { for(banner in it){ Log.e("awaitBanner",banner.title) } }

    /**
     * 不处理异常 异常会直接抛出，统一处理
     */
    val awaitBannerError = service.awaitBanner().await()
}

}

/* * 串行 await / fun serial(){ lifecycleScope.launch { //先调用第一个接口await val awaitBanner1 = service.awaitBanner().await() //第一个接口完成后调用第二个接口 val awaitBanner2 = service.awaitBanner().await() } }

/* * 并行 async / fun parallel(){ lifecycleScope.launch { val awaitBanner1 = service.awaitBanner().async(this) val awaitBanner2 = service.awaitBanner().async(this)

    //两个接口一起调用
    awaitBanner1.await()
    awaitBanner2.await()
}

} ```

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