在定义到方法中的类上使用Gson返回null

Question

I'm have a class that i only need in one method.. so i have declared it in the method.

and now when i try to convert an object from this class to json using gson i get null.

my code is something like this:

private Response performGetClientDetails(HashMap<String, Object> requestMap) {

        class ClientDetails {
            String id;
            String name;
            String lastName;
            int accoundId;

            public ClientDetails(String id, String name, String lastName, int accoundId) {
                this.id = id;
                this.name = name;
                this.lastName = lastName;
                this.accoundId = accoundId;
            }
        }

        ClientDetails clientDetails = new ClientDetails(client.getId(), client.getFirstName(), client.getLastName(), client.getAccount().getId());
        Gson gson = new Gson();
        return new Response(true, gson.toJson(clientDetails));
    }

what is returning null is this: gson.toJson(clientDetails) .. its supposed to return a json string.

Answer 1

According to GSON Docs :

" Gson can not deserialize {"b":"abc"} into an instance of B since the class B is an inner class. if it was defined as static class B then Gson would have been able to deserialize the string. Another solution is to write a custom instance creator for B. "

public class InstanceCreatorForB implements InstanceCreator<A.B> {
  private final A a;
  public InstanceCreatorForB(A a)  {
    this.a = a;
  }
  public A.B createInstance(Type type) {
    return a.new B();
  }
}

The above is possible, but not recommended.

Since you're using a non-static inner class, Gson will not be able to serialize the object.

You can try the second solution, which is not recommended, to use on your case or simply declare the ClientDetails class by itself, which will work fine.