gson.fromJson return null values

Since you are setting excludeFieldsWithoutExposeAnnotation() configuration on the GsonBuilder you must put @Expose annotation on those fields you want to serialize/deserialize.

So in order for excludeFieldsWithoutExposeAnnotation() to serialize/deserialize your fields you must add that annotation:

@Expose
private String userName;
@Expose
private String password;

Or, you could remove excludeFieldsWithoutExposeAnnotation() from the GsonBuilder.