Error parsing field as object or array

Question

i have the following Json string, which I\'m suppose to deserialize. The problem is: since this string comes from a server I can\'t change it and I need to deserialize as PO

Answer 1

You can use TypeAdapterFactory to do the conversion. Here is a factory that will add that functionality to all of your List member types --

import com.google.gson.Gson;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.Collections;
import java.util.List;

public class SingletonListTypeAdapterFactory implements TypeAdapterFactory {
     public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {

       Type type = typeToken.getType();
       if (typeToken.getRawType() != List.class
           || !(type instanceof ParameterizedType)) {
         return null;
       }
       Type elementType = ((ParameterizedType) type).getActualTypeArguments()[0];
       TypeAdapter<?> elementAdapter = gson.getAdapter(TypeToken.get(elementType));
       TypeAdapter<T> arrayAdapter = gson.getDelegateAdapter(this, typeToken);
       return (TypeAdapter<T>) newSingtonListAdapter((TypeAdapter<Object>) elementAdapter, (TypeAdapter<List<Object>>) arrayAdapter);
     }

     private <E> TypeAdapter<List<E>> newSingtonListAdapter(
         final TypeAdapter<E> elementAdapter,
         final TypeAdapter<List<E>> arrayAdapter) {
       return new TypeAdapter<List<E>>() {

         public void write(JsonWriter out, List<E> value) throws IOException {
           if(value == null || value.isEmpty()) {
             out.nullValue();
           } else if(value.size() == 1) {
            elementAdapter.write(out, value.get(0));
           } else {
             arrayAdapter.write(out, value);
           }
         }

         public List<E> read(JsonReader in) throws IOException {
           if (in.peek() != JsonToken.BEGIN_ARRAY) {
             E obj = elementAdapter.read(in);
             return Collections.singletonList(obj);
           }
           return arrayAdapter.read(in);
         }
       };
     }
   }

As bonus, it also serializes in the same way, if needed. If you also want to serialize as array, replace the write method with a call to arrayAdapter.write.

To you, add to your gson when building --

Gson gson = new GsonBuilder().registerTypeAdapterFactory(new SingletonListTypeAdapterFactory())
        .create();