如何使用 Retrofit2、Gson 和 Rx 处理多种可能的响应类型

Question

我必须使用的 API 很糟糕，总是返回 HTTP 200。但有时会有正确的响应：

[{"blah": "blah"}, {"blah": "blah"}]

有时会出现错误：

{"error": "Something went wrong", "code": 123}

我正在使用带有 Gson 转换器和 Rx 适配器的 Retrofit2：

final Api api = new Retrofit.Builder()
        .baseUrl(URL)
        .client(client)
        .addCallAdapterFactory(RxJavaCallAdapterFactory.createWithScheduler(Schedulers.io()))
        .addConverterFactory(GsonConverterFactory.create())
        .build()
        .create(Api.class);

现在，当我收到错误响应时，将调用 onError 处理程序，但出现以下异常：

java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 2 path $
    at com.google.gson.stream.JsonReader.beginArray(JsonReader.java:350)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:80)
    at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
    at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:37)
    at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:25)
    at retrofit2.ServiceMethod.toResponse(ServiceMethod.java:117)
    at retrofit2.OkHttpCall.parseResponse(OkHttpCall.java:211)
    at retrofit2.OkHttpCall.execute(OkHttpCall.java:174)
    at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$RequestArbiter.request(RxJavaCallAdapterFactory.java:171)
    at rx.internal.operators.OperatorSubscribeOn$1$1$1.request(OperatorSubscribeOn.java:80)
    at rx.Subscriber.setProducer(Subscriber.java:211)
    at rx.internal.operators.OperatorSubscribeOn$1$1.setProducer(OperatorSubscribeOn.java:76)
    at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$CallOnSubscribe.call(RxJavaCallAdapterFactory.java:152)
    at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$CallOnSubscribe.call(RxJavaCallAdapterFactory.java:138)
    at rx.Observable.unsafeSubscribe(Observable.java:10144)
    at rx.internal.operators.OperatorSubscribeOn$1.call(OperatorSubscribeOn.java:94)
    at rx.internal.schedulers.CachedThreadScheduler$EventLoopWorker$1.call(CachedThreadScheduler.java:230)
    at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:428)
    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:272)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
    at java.lang.Thread.run(Thread.java:761)

我该如何解决？如果我能在onError 处理程序中得到响应，我可以用适当的错误模型类重新解析它。但似乎我无法得到原始响应。

Answer 1

您可以使用自定义 Gson 反序列化器将两个响应编组为单个对象类型。这是一个粗略的想法，假设您当前的响应类型是List<Map<String, String>>，您需要根据您的实际返回类型进行调整。我还假设 API 总是在成功时返回一个数组——

public class MyResponse {
  String error;
  Integer code;
  List<Map<String, String>> response;
}

interface MyApi {
  @GET("/")
  Observable<MyResponse> myCall();
}

private class MyResponseDeserializer implements JsonDeserializer<MyResponse> {
  public MyResponse deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
      throws JsonParseException {
    MyResponse response = new MyResponse();
    if (json.isJsonArray()) {
      // It is an array, parse the data
      Type responseType = new TypeToken<List<Map<String, String>>>(){}.getType();
      response.response = context.deserialize(json, responseType);
    } else {
      // Not an array, parse out the error info
      JsonObject object = json.getAsJsonObject();
      response.code = object.getAsJsonPrimitive("code").getAsInt();
      response.error = object.getAsJsonPrimitive("error").getAsString();
    }
    return response;
  }
}

使用上述创建自定义Gson

Gson gson = new GsonBuilder()
    .registerTypeAdapter(MyResponse.class, new MyResponseDeserializer())
    .create();

在您的改造构建器中使用它 --

.addConverterFactory(GsonConverterFactory.create(gson))

您还应该更新您的界面以返回Observable<MyResponse>。您现在将在onNext 中获得成功和错误。您需要检查对象以确定它是否是成功响应 (response != null)。