parse JSON with GSON returns null

问题

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????

回答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!

回答2:

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

来源：https://stackoverflow.com/questions/22720966/parse-json-with-gson-returns-null

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java

android

json

gson