Question

I have a problem on converting JSON string to object in Android. Here are the JSON structure and Java classes:

JSON:

{
"code":"SUCCEED",
"message":"",
"result":{
    "ccahUserId": 111,
    "ccahUserName":"your_name",
    "userFirstName":"your_first_name",
    "userLastName":"your_last_name",

    //others
}

Java classes:

public class Result<T>{
   public String code;
   public String message;
   public T result;   
}

public class DeviceSetting 
{
    public long ccahUserId;
    public String ccahUserName;
    public String userFirstName;
    public String userLastName;
    //other members

}

Activity:

Gson gson = new Gson();
Result<DeviceSetting> setting = gson.fromJson(result, Result<DeviceSetting>.class);

When I deserialise the JSON string, code and message field were good but result field is null.
I am not familiar with Gson yet, so please help how to fix this problem?

Thanks in advance.

Answer 1

Likely the result field is null because it relies on the type parameter for Result.

From the GSON documentation for Gson.fromJson(JsonElement, Class<T>) (bolding is mine):

This method deserializes the Json read from the specified parse tree
into an object of the specified type. It is not suitable to use if the
specified class is a generic type since it will not have the generic
type information because of the Type Erasure feature of Java. Therefore, this method should not be used if the desired type is a generic type. Note that this method works fine if the any of the fields of the specified object are generics, just the object itself should not be a generic type. For the cases when the object is of generic type, invoke fromJson(JsonElement, Type).