Receive response from a restful web service java on Android

I'm developing an Android application and would like to know how do I get a response from the server, the technology I'm using on Android is the retrofit 2. After sending a POST request, how do I get a response from the server and from that information do an "if" in Android's onResponse method. When I run the application it gives an error on the server, in that case I would just like to receive a true or false so that from this answer I can mount my conditions in the application.

Follow my code in the Web service:

@POST
    @Consumes({"application/json"})
    @Path("Usuario/inserir")
    public boolean inserirUsuario(String content) {
        Gson g = new Gson();
        try{
            //JsonReader reader = new JsonReader(new StringReader(content));
            //reader.setLenient(true);
            Usuario u = (Usuario) g.fromJson(content, Usuario.class);
            UsuarioBusiness ub = new UsuarioBusiness();
            System.out.println("Teste saida: " + ub.inserir(u));
            return ub.inserir(u);

        } catch (Exception e){
            throw new NoContentException(content);
        } 
    }

Here is the code for the insert method in the Business package:

public boolean inserir(Usuario usuario) {
        UsuarioDAO dao = new UsuarioDAO();
        if(dao.inserir(usuario) > 0){
            return true;
        } else {
            return false;
    }
}

Follow my code on Android:

call.enqueue(new Callback<Usuario>() {
                        @Override
                        public void onResponse(Call<Usuario> call, Response<Usuario> response) {
                            if(response.isSuccessful()) {
                                AlertDialog.Builder dialogo1 = new AlertDialog.Builder(MainActivity.this);
                                dialogo1.setTitle("Sucesso");
                                dialogo1.setMessage("Usuario cadastrado com sucesso!");
                                dialogo1.setNeutralButton("ok", null);
                                dialogo1.show();
                            } else {
                                AlertDialog.Builder dialogo1 = new AlertDialog.Builder(MainActivity.this);
                                dialogo1.setTitle("Duplicidade");
                                dialogo1.setMessage("Usuario não cadastrado!");
                                dialogo1.setNeutralButton("ok", null);
                                dialogo1.show();
                            }
                        }

                        @Override
                        public void onFailure(Call<Usuario> call, Throwable t) {
                            txtResult.setText(t.getLocalizedMessage());
                            Log.d("my_tag", "ERROR: " + t.getMessage());
                            Log.d("my_tag", "ERROR: " + t.toString());
                        }
                    });
            }
            });