# Java/Kotlin JSON parsing improvement

I consume an API which gives me this type of JSON:

{
"data": {
"name": "Start",
"pid": "1",
"position": {
"data": {
"x": "31",
"y": "330"
},
}
},
}


I have created the classes with objects with the same structure as the above JSON. I use the retrofit lib in Android which inside uses GSON for parsing the JSON.

My model classes would be like this:

MResponse.class

public class MResponse {

@SerializedName("data")
public User user;

}


User.class

public class User {

public String name;

public String pid;

@SerializedName("position")
public PositionData positionData;
}


PositionData.class

public class PositionData {

@SerializedName("data")
public Position position;

}


Position.class

public class Position {

public String x;

public String y;
}


Now this works fine for me. But as you can see for every model I have to create a parent which will have the same structure just changes the child. This fact doubles the classes that I use for my models. I would like to ask if there is a better way to avoid all these classes.

I don't want to use inner classes. I was thinking that the guys that have done the JSON like this must have had a reason why they did it like this and also a way to make the parsing more easier.

Usually I was used to parse this kind of JSON structure:

{
"data": {
"name": "Start",
"pid": "1",
"position": {
"x": "31",
"y": "330"
}
}
}


And here it's easier if I would follow the solution above.

EDIT

Also any solution in Kotlin is welcomed

You can create a generic container/entity for "data" and "metadata" and reuse it. e.g.:

data class MEntity<T>(
var data: T? = null,
)

data class User(
var name: String? = null,
var pid: String? = null,
var position: MEntity<Position>? = null
)

data class Position(
var x: String? = null,
var y: String? = null
)


Due to type erasure you must use a TypeToken to deserialize the JSON into a generic type:

gson.fromJson<MEntity<User>>(json, object : TypeToken<MEntity<User>>() {}.type)


This isn't very convenient but thankfully Kotlin allows us to use reified type parameters to define an extension function to simplify this:

inline fun <reified T> Gson.fromJsonToGeneric(json: String): T {
return fromJson(json, object : TypeToken<T>() {}.type)
}


Now the usage becomes much simpler:

val userMEntity = gson.fromJsonToGeneric<MEntity<User>>(json)
println(userMEntity)


Output:

MEntity(data=User(name=Start, pid=1, position=MEntity(data=Position(x=31, y=330), metadata=empty)), metadata=empty)


Well the solution that I was asking for was quite simple in my opinion, I just didn't know it in the beginning. I found this times ago but now I want to write it here. I haven't used the Kotlin solution mentioned from @mfulton but I think that it's also the right answer.

Based on source code of Retrofit and some other related answers about Java generics this was the answer for my problem:

public class DataResponse<T, R> {

public T data;

@SerializedName("meta")

Observable<DataResponse<User, BaseMeta>> getUser()