Android Studio java.lang.IllegalStateException：应为 BEGIN_ARRAY，但在第 1 行第 2 列路径 $ 处为 BEGIN_OBJECT

Question

我知道这不是关于此错误的第一个问题。我到处寻找答案，但找不到解决办法。当我运行代码时，我得到了这个异常；

java.lang.IllegalStateException：应为 BEGIN_ARRAY，但在第 1 行第 2 列路径 $

处为 BEGIN_OBJECT

主要活动

public class MainActivity extends AppCompatActivity {
    ArrayList<Doviz> dovizs;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Retrofit retrofit= new Retrofit.Builder()
                .baseUrl("https://finans.truncgil.com/")
                .addConverterFactory(GsonConverterFactory.create())
                .build();
        DovizApi dovizApi = retrofit.create(DovizApi.class);

        Call<List<Doviz>> call = dovizApi.getDoviz();

      

        call.enqueue(new Callback<List<Doviz>>() {

            @Override
            public void onResponse(Call<List<Doviz>> call, Response<List<Doviz>> response) {
                System.out.println("deneme");
                List<Doviz> responseList= response.body();
                dovizs = new ArrayList<>(responseList);
                System.out.println(dovizs.get(0).USD);

            }

            @Override
            public void onFailure(Call<List<Doviz>> call, Throwable t) {
                System.out.println(t.fillInStackTrace());
            }
        });
    }
}

Java 类

public class Doviz {

    @SerializedName("Buying")
    public String USD;

}

界面

public interface DovizApi {
    @GET("today.json")
    Call<List<Doviz>> getDoviz();
}

我使用的列表 https://finans.truncgil.com/v3/today.json

我已经处理这个问题好几天了。我希望我们能解决它

Answer 1

发生了什么？

• API 响应的根是 JSONObject 而不是 JSONArray。
• API URL 中缺少 v3。

解决方案

更新界面

public interface DovizApi {
    @GET("v3/today.json")
    Call<HashMap<String, Object>> getDoviz();
}

更新响应模型（Doviz）

public class Doviz {
   @SerializedName("Buying")
   public String buying;

   // Similarly you can add other keys here
}

更新改造调用

Call<HashMap<String, Object>> call = dovizApi.getDoviz();
call.enqueue(new Callback<HashMap<String, Object>>() {

        @Override
        public void onResponse(Call<HashMap<String, Object>> call, Response<HashMap<String, Object>> response) {
            HashMap<String, Object> responseModel = response.body();

            // Iterate all the currencies
            for (Map.Entry<String, Object> entry : responseModel.entrySet())
                if(entry.getValue() instanceof LinkedTreeMap) { // Since the first element is of type String i.e. "Update_Date"
                    Doviz doviz = new Gson().fromJson(new Gson().toJson(((LinkedTreeMap<String, Object>) entry.getValue())), Doviz.class);
                    System.out.println("Currency = " + entry.getKey() +
                                     ", Buying = " + doviz.buying);
                }
        }

        @Override
        public void onFailure(Call<HashMap<String, Object>> call, Throwable t) {
            System.out.println(t.fillInStackTrace());
        }
    });

Answer 2

检查点

1. 类型

Json 如下所示

{
   "Update_Date":"2021-05-12 16:00:01",
   "USD":{
      "Buying":"8,3681",
      "Type":"Currency",
      "Selling":"8,3735",
      "Change":"%1,13"
   },
   ...
}

这不是<List> 和USD 是json 中的关键之一

所以Call<List<Doviz>> 应该更改为Call<Doviz>

1. DTO（多维兹）

您可能希望Buying 的值为USD。 你是 DTO(Doviz) 应该拥有像这样的另一个 DTO 的属性

  class Doviz {
        @SerializedName("USD")
        CurrencyInfo usd;
       
        // else like this
        @SerializedName("EUR")
        CurrencyInfo eur;

        //...
  }

  class CurrencyInfo {
        //if Path(/v3) included
        @SerializedName("Buying")
        String buying;

        //if Path (/v3) not included 
        @SerializedName("Alış")
        String _buying;

       // else.. 
 }

interface DovizApi{
        @GET("/v3/today.json")
        fun getEnDoviz(): Call<Doviz>
}

Call<Doviz> call = dovizApi.getDoviz();
call.enqueue(new Callback<Doviz>(){
            @Override
            public void onResponse(Call<Doviz> call,Response<Doviz>response){
                Doviz doviz = response.body();
                CurrencyInfo info = doviz.getUsd();
                System.out.println(info.getBuying());
            }
..
}

效果很好。