parse JSON with GSON returns null

Question

Here is my Json :

[
{
"canaldsc":"PHARMA",
"cadenadsc":null,
"formatodsc":"DEL AHORRO",
"estadodsc":null,
"ciudaddsc":"VALLE DE MEXICO",
"regiondsc":"CENTRO SUR",
"proyectotiendaid":null,
"proyectoid":"79",
"planid":"54",
"proyectodsc":"Concurso",
"vigencia":"0000-00-00",
"activo":"1",
"usuarioproyectotiendaid":"65280",
"proyecto":null,
"fechainicio":"2014-03-24",
"lunes":"7",
"martes":"7",
"miercoles":"7",
"jueves":"7",
"viernes":"7",
"sabado":"7",
"domingo":"7"
},
{
"canaldsc":"PHARMA",
"cadenadsc":null,
"formatodsc":"DEL AHORRO",
"estadodsc":null,
"ciudaddsc":"VALLE DE MEXICO",
"regiondsc":"CENTRO SUR",
"proyectotiendaid":null,
"proyectoid":"79",
"planid":"54",
"proyectodsc":"Concurso",
"vigencia":"0000-00-00",
"activo":"1",
"usuarioproyectotiendaid":"65284",
"proyecto":null,
"fechainicio":"2014-03-24",
"lunes":"7",
"martes":"7",
"miercoles":"7",
"jueves":"7",
"viernes":"7",
"sabado":"7",
"domingo":"7"
}
]

In reality, there is more than 2 objects, but I cut it to simplify

My Model Class :

public class PdvResult {
public PdvResult() {
}

public String canaldsc;
public String cadenadsc;
public String formatodsc;
public String estadodsc;
public String ciudaddsc;
public String regiondsc;
public String proyectotiendaid;
public String proyectoid;
public String planid;
public String proyectodsc;
public String vigencia;
public String activo;
public String usuarioproyectotiendaid;
public String proyecto;
public String fechainicio;
public String lunes;
public String martes;
public String miercoles;
public String jueves;
public String viernes;
public String sabado;
public String domingo;
}

It should be corresponds in the names so that the mapping can happen.

In my Java, I use

List<PdvResult> pdvs = (List<PdvResult>)gson.fromJson(reader, new TypeToken<PdvResult>() {}.getType());

but pdvs return null.

What's wrong with my code????

Your `TypeToken` is incorrect. It should have a type argument of `>`. — Sotirios Delimanolis, Mar 28 '14 at 18:55
I changed it, but still give me null ! - it's also giving me a warning in this line : Type safety: Unchecked cast from Object to List — Juliatzin, Mar 28 '14 at 19:01
Can you change the JSON definition ??? I would add a name to the array value. Like { "pdvs": [ {...}, {...}] } — hmartinezd, Mar 28 '14 at 19:29

score 1 · Accepted Answer · answered Mar 28 '14 at 21:58

1

Change the line where you parse the JSON, use this:

List<PdvResult> pdvs = gson.fromJson(reader, new TypeToken<List<PdvResult>>() {}.getType());

You are using TypeToken<PdvResult>, and you have to use TypeToken<List<PdvResult>>, otherwise you're trying to parse your JSON into a PdvResult object, while you actually have an array of PdvResult objects!

answered Mar 28 '14 at 21:58

MikO

18,243
12
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@Sotirios Delimanolis already told me this, but it's not working. Guess I will parse it without Gson ! – Juliatzin Mar 28 '14 at 22:17
@JuliatzindelToro, are you getting any Exception? Otherwise I'd suggest you to check your `reader`, maybe for some reason you're not reading the JSON correctly, so you're getting `null`... – MikO Mar 28 '14 at 23:04
@JuliatzindelToro, really weird... And are you sure your JSON is EXACTLY like what you wrote, it starts and ends with `[ ... ]` and contains only a number of equal objects `{ ... }`? – MikO Mar 29 '14 at 10:57

Braj · Answer 2 · 2014-03-28T19:23:43.743

0

The best way of checking the type of returned JSON object is explained below:

Start form Object class

Object result= gson.fromJson(reader,Object.class);
System.out.println(result.getClass().getName());

It will return java.lang.ArrayList

Do the same operation of ArrayList

System.out.println(((ArrayList)result).size());
System.out.println(((ArrayList)result).get(0).getClass().getName());

Now it will print the name of class stored in ArrayList
Repeat the same operation till leaf nodes
Finally form the resultant JSON object as expected by inspecting object and class type

edited Mar 28 '14 at 19:23

answered Mar 28 '14 at 19:14

Braj

46,415
5
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I am using `com.google.gson.Gson` and its working fine for me. What are you using. – Braj Mar 28 '14 at 19:29
My output is `java.util.ArrayList 2 com.google.gson.internal.StringMap` – Braj Mar 28 '14 at 19:30
Here is my rest code : `Reader reader=new FileReader(new File("resources/abc.txt")); Gson gson=new Gson(); Object result= gson.fromJson(reader,Object.class);` – Braj Mar 28 '14 at 19:32

parse JSON with GSON returns null

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