Gson deserialize generic list into a generic method

Question

When I have a list inside a generic method Gson returns a list of Object instead a list of generic type. I've seen a lot of threads with no solution, and if I dont use a generic method would have to create a method for each bean.

Is there any one with any idea what do I have to do so solve it?

PS: For a while I've created loop into the list to serialize entity by entity, splitting returned String and deserializing entity by entity, but clearly it's a workaround

Creating a generic list and serializing to JSON (this is a webservices method):

public String listEntity(String nomeClasse) throws WsException {
    // Identifying the entity class
    Class<?> clazz = Class.forName(nomeClasse);

    // Querying with Hibernate
    List<?> lst = getDao().listEntity(clazz);

    // Check if is null
    if (lst == null) {
        return "[]";
    }

    return gson.toJson(lst);
}

Consuming the Webservice method:

public <T> List<T> listEntity(Class<T> clazz)
        throws WsIntegracaoException {
    try {
        // Consuming remote method
        String strJson = getService().listEntity(clazz.getName());

        Type type = new TypeToken<List<T>>() {}.getType();

        // HERE IS THE PROBLEM
        List<T> lst =  GSON.fromJson(strJson, type);
        // RETURNS IS A LIST OF OBJECT INSTEAD OF A LIST OF <T>

        return lst;

    } catch (Exception e) {
        throw new WsIntegracaoException(
                "WS method error [listEntity()]", e);
    }
}

Invoking the generic method:

List<City> list =  listEntity(City.class);
// Here I get a ClassCastException
fillTable(list);

List Element (wrong):

java.lang.Object@23f6b8

Exception:

java.lang.ClassCastException: java.lang.Object cannot be cast to java.io.Serializable

Incorretily maked as answered by Sotirios Delimanolis, this was the correct answer: http://stackoverflow.com/questions/21176195/deserialize-json-string-into-generically-typed-list?rq=1 — Rodrigo Tavares, Aug 05 '14 at 16:27
You can always reply with `@username` so that that user is notified. — Sotirios Delimanolis, Aug 05 '14 at 22:51

score 4 · Accepted Answer · edited May 23 '17 at 12:08

SOLUTION - THIS WORKED FOR ME: Gson TypeToken with dynamic ArrayList item type

public <T> List<T> listEntity(Class<T> clazz)
        throws WsIntegracaoException {
    try {
        // Consuming remote method
        String strJson = getService().listEntity(clazz.getName());

        JsonParser parser = new JsonParser();
        JsonArray array = parser.parse(strJson).getAsJsonArray();

        List<T> lst =  new ArrayList<T>();
        for(final JsonElement json: array){
            T entity = GSON.fromJson(json, clazz);
            lst.add(entity);
        }

        return lst;

    } catch (Exception e) {
        throw new WsIntegracaoException(
                "WS method error [listEntity()]", e);
    }
}

Gson deserialize generic list into a generic method

1 Answers1