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deserialize json string with gson

Posted by: admin December 28, 2021 Leave a comment

Questions:

My java servlet returns a json string in this way:

Gson gson = new Gson();     
String lista = gson.toJson(utenti);
System.out.println(lista);
request.setAttribute("lista", lista);
request.getRequestDispatcher("GestioneUtenti.jsp").forward(request, response);

now, in the jsp page I want to have my arrayList again. I try to do this:

<%
String lista = (String)request.getAttribute("lista");
Gson gson = new Gson();
ArrayList<Utente> users = gson.fromJson(lista, TypeToken.get(new ArrayList<Utente>().getClass()).getType());        
out.println(users.get(0).getUsername());
%>

I have this exception:

java.lang.ClassCastException: com.google.gson.internal.StringMap cannot be cast to classi.Utente

can Youu help me? If i miss some particulars tell me! thanks 🙂

Answers:

I solved with this code:

String lista = (String)request.getAttribute("lista");
Gson gson = new Gson();                         
Type listType = new TypeToken<ArrayList<Utente>>() {}.getType();
ArrayList<Utente> users = new Gson().fromJson(lista, listType);

###

It suggests you have a StringMap where you have declared a Utente class. The source of the error is more than likely your users list