Serialize response object with generic nested data object with GSON - json

Question

I am using Retrofit with GSON for JSON serialization and Realm for storage.
My JSON Responses always look like (simplyfied)
{
status : 1
data: { object data }
}
So I have meta information and a data root object which contains the result (object or array)
Now I am trying to write a custom deserializer for GSON which converts the result to a object or list of objects.
For me it only works with static object type definitions like:
public class ResponseDeserializer implements JsonDeserializer {
#Override
public Object1 deserialize(JsonElement je, Type type, JsonDeserializationContext jdc)
{
JsonElement data = je.getAsJsonObject().get("data");
GsonBuilder gsonBuilder = new GsonBuilder()
.setExclusionStrategies(new ExclusionStrategy() {
#Override
public boolean shouldSkipField(FieldAttributes f) {
return f.getDeclaringClass().equals(RealmObject.class);
}
#Override
public boolean shouldSkipClass(Class<?> clazz) {
return false;
}
});
Gson gson = gsonBuilder.create();
Object1 o1 = gson.fromJson(data, new TypeToken<Object1>() {}.getType());
return o1;
}
}
First question: When I try to change to a generic type fromJson results in an "com.google.gson.internal.LinkedTreeMap" with key value pairs of the object, code:
public class ResponseDeserializer<T> implements JsonDeserializer<T> {
#Override
public T deserialize(JsonElement je, Type type, JsonDeserializationContext jdc)
{
JsonElement data = je.getAsJsonObject().get("data");
GsonBuilder gsonBuilder = new GsonBuilder()
.setExclusionStrategies(new ExclusionStrategy() {
#Override
public boolean shouldSkipField(FieldAttributes f) {
return f.getDeclaringClass().equals(RealmObject.class);
}
#Override
public boolean shouldSkipClass(Class<?> clazz) {
return false;
}
});
Gson gson = gsonBuilder.create();
T o = gson.fromJson(data, new TypeToken<T>() {}.getType());
return o;
}
}
Second question: How can the deserializer return an object or a list of objects depending on the json result.

Answer 1

Now I have solved it with an different approach:
2 response models for list and object:
public class ApiResponse<T> {
private int success;
private String[] errors;
private String[] messages;
private T data;
}
public class ApiListResponse<T> {
private int success;
private String[] errors;
private String[] messages;
private List<T> data;
}
1 deserializer for the response models
public class ResponseDeserializer<T> implements JsonDeserializer {
#Override
public T deserialize(JsonElement je, Type type, JsonDeserializationContext jdc) throws JsonParseException {
JsonElement data = je.getAsJsonObject().get("data");
GsonBuilder gsonBuilder = new GsonBuilder()
.setExclusionStrategies(new ExclusionStrategy() {
#Override
public boolean shouldSkipField(FieldAttributes f) {
return f.getDeclaringClass().equals(RealmObject.class);
}
#Override
public boolean shouldSkipClass(Class<?> clazz) {
return false;
}
});
Gson gson = gsonBuilder.create();
T response = gson.fromJson(je, type);
return response;
}
}
And now i can register types for GSON like:
gsonBuilder.registerTypeAdapter(new TypeToken<ApiResponse<Object1>>() {}.getType(), new ResponseDeserializer<ApiResponse>());
gsonBuilder.registerTypeAdapter(new TypeToken<ApiListResponse<Object1>>() {}.getType(), new ResponseDeserializer<ApiListResponse>());
And now the following JSON responses will be converted correctly:
ApiResponse
{
"data":{
"Object1Id":"1",
"Name":"Test 1",
},
"messages":[
],
"errors":[
],
"success":"1"
}
ApiListResponse
{
"data":[{
"Object1Id":"1",
"Name":"Test 1",
},{
"Object1Id":"2",
"Name":"Test 2",
}],
"messages":[
],
"errors":[
],
"success":"1"
}
Are there better solutions?