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
interface TestServer {
@GET("banner/json")
suspend fun banner(): ApiResponse<List<Banner>>
}
//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
interface TestServer {
@GET("banner/json")
suspend fun awaitBanner(): Await<List<Banner>>
}
//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()
}
}
3.查看Retrofit源码
先看Retrofit create方法
public <T> T create(final Class<T> 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
我们查看suspenForResponse中的adapt
@Override
protected Object adapt(Call<ResponseT> 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。
class ApiResultCallAdapterFactory : CallAdapter.Factory() {
override fun get(returnType: Type, annotations: Array<Annotation>, retrofit: Retrofit): CallAdapter<*, *>? {
//检查returnType是否是Call<T>类型的
if (getRawType(returnType) != Call::class.java) return null
check(returnType is ParameterizedType) { "$returnType must be parameterized. Raw types are not supported" }
//取出Call<T> 里的T，检查是否是Await<T>
val apiResultType = getParameterUpperBound(0, returnType)
// 如果不是 Await 则不由本 CallAdapter.Factory 处理 兼容正常模式
if (getRawType(apiResultType) != Await::class.java) return null
check(apiResultType is ParameterizedType) { "$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<T>(private val type: Type) : CallAdapter<T, Call<Await<T>>> {
override fun responseType(): Type = type
override fun adapt(call: Call<T>): Call<Await<T>> {
return ApiResultCall(call)
}
}
class ApiResultCall<T>(private val delegate: Call<T>) : Call<Await<T>> {
/**
* 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<Await<T>>) {
//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(this@ApiResultCall, Response.success(delegate.toResponse()))
}
}
internal class AwaitImpl<T>(
private val call : Call<T>,
) : Await<T> {
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。
@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
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
/**
* 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
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
implementation “io.github.cnoke.ktnet:api:?”
写一个网络请求数据基类
open class ApiResponse(
var data: T? = null,
var errorCode: String = “”,
var errorMsg: String = “”
)
实现com.cnoke.net.factory.GsonResponseBodyConverter
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
interface TestServer {
@GET(“banner/json”)
suspend fun awaitBanner(): Await<List>
}
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。
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()}
}
本文转自 [https://juejin.cn/post/7051437444062773285](https://juejin.cn/post/7051437444062773285)，如有侵权，请联系删除。