(Gson) JSON to Java objects containing ArrayList<Class>

Question

I'm retrieving data from a Web Service, which returns a String with the JSON representation of my object. What happens is that my object has two ArrayList<> of other objects, besides of other simple attributes. It seems to be a problem for the Gson. I've been searching and the answers do not match my specific problem.

My code is, basically:

Verbete

public class Verbete implements Serializable{
    private long id;
    private List<NomesVerbete> nomes;
    private List<SignificadosVerbete> significados;
    private int totalAcessos = 0;
    private Date dataLancamento;
    private int relevancia = 0;
    //getters and setters
}

NomesVerbete

public class NomesVerbete implements Serializable {
    private long id;
    private String nome;
    private String etimologia;
    //getters and setters
}

SignificadosVerbete

public class SignificadosVerbete implements Serializable{
    private long id;
    private String significado;
    private CategoriaVerbete categoria;
    //getters and setters
}

CategoriaVerbete

public class CategoriaVerbete implements Serializable{
    private long id;
    private String nome;
    private String descricao;
    private int serie;
    //getters and setters
}

The conversion from Verbete to JSON gives me this String (which seems to be correct, right?):

{"id":81,"nomes":[{"id":124,"nome":"aleluia","etimologia":"asasiajisjaijs"},{"id":126,"nome":"amém","etimologia":"asasiajisjaijs"}],"significados":[{"id":67,"significado":"asasjaijsiajsoijaoisjaoisj","categoria":{"id":3,"nome":"Nada","descricao":"asuahushaus","serie":1}}],"totalAcessos":0,"dataLancamento":1382066568000,"relevancia":0}

But, when I try to convert this JSON string to Verbete, it doesn't work, comproved by the NullPointerException that I get when trying to access the object. Here's is my conversion from Json:

Gson gson = new GsonBuilder().create();
Verbete verbete = gson.fromJson(resposta[1], Verbete.class); //resposta[1] is the json string above

Could someone give me a way to go in this conversion, please? Thank you.

LogCat just show a NullPointerException when I try to access the "verbete" object. — vitorgreati
– vitorgreati, Commented Nov 10, 2013 at 15:23
I seriously doubt it. Show us an SSCCE reproducing the problem. — JB Nizet
– JB Nizet, Commented Nov 10, 2013 at 15:26
I'm guessing you're either feeding the parser a null string or you're not actually checking the result from the parser. — Hot Licks
– Hot Licks, Commented Nov 10, 2013 at 15:27
The String resposta[1] actually has the Json string. As I can see, my code should work correctly, right? — vitorgreati
– vitorgreati, Commented Nov 10, 2013 at 15:34

Prabhakaran Ramaswamy · Accepted Answer · 2013-11-10 16:19:45Z

1

do like this

    final String json = "{\"id\":81,\"nomes\":[{\"id\":124,\"nome\":\"aleluia\",\"etimologia\":\"asasiajisjaijs\"},{\"id\":126,\"nome\":\"amém\",\"etimologia\":\"asasiajisjaijs\"}],\"significados\":[{\"id\":67,\"significado\":\"asasjaijsiajsoijaoisjaoisj\",\"categoria\":{\"id\":3,\"nome\":\"Nada\",\"descricao\":\"asuahushaus\",\"serie\":1}}],\"totalAcessos\":0,\"dataLancamento\":1382066568000,\"relevancia\":0}";
    GsonBuilder gsonBuilder = new GsonBuilder();
    gsonBuilder.registerTypeAdapter(Date.class,
            new JsonDeserializer<Date>() {
                @Override
                public Date deserialize(JsonElement jsonElement, Type type,
                        JsonDeserializationContext context)
                        throws JsonParseException {
                    Calendar calendar = Calendar.getInstance();
                    calendar.setTimeInMillis(jsonElement.getAsLong());
                    return calendar.getTime();
                }
            });
    Gson gson = gsonBuilder.create();
    Verbete verbete = gson.fromJson(json, Verbete.class);

    System.out.println(verbete);

answered Nov 10, 2013 at 16:19

Prabhakaran Ramaswamy

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1 Comment

vitorgreati Over a year ago

Interesting! It worked! So, the problem was in to convert from milliseconds to Date object?

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