将jsonobject追加到现有的jsonobject

Question

I'm having a problem with Json file reading and writing. I want to append something into a json file but it doesn't work properly: it just put in a new jsonobject without the ' , ' to divide it from the previous one. I searched everywhere, on every site, but nothing that gave me an input on how to do it properly.

For example, I have a json file like this:

{
    "Example":{
        "Ok":"Ok1",
        "Nice":"Nice1",
        "Hi":"Hi1",
        "Hello":"Hello1",
        "Right":"Right1",
        "Wow":"Wow1"
    }
}

And I want to make it appear like this:

{
    "Example":{
        "Ok":"Ok1",
        "Nice":"Nice1",
        "Hi":"Hi1",
        "Hello":"Hello1",
        "Right":"Right1",
        "Wow":"Wow1"
    },
    "Example1":{
        "Ok":"Ok2",
        "Nice":"Nice2",
        "Hi":"Hi2",
        "Hello":"Hello2",
        "Right":"Right2",
        "Wow":"Wow2"
    }
}

So, I tried using this code:

Gson gson = new GsonBuilder().setPrettyPrinting().create();
JsonObject jsonObject = new JsonObject();
JsonObject dati = new JsonObject();
dati.addProperty("Cognome", StringUtils.capitalize((fields[0].getText())));
dati.addProperty("Nome", StringUtils.capitalize((fields[1].getText())));
dati.addProperty("Sesso", lblSesso.getText());
dati.addProperty("Luogo di nascita", StringUtils.capitalize((fields[2].getText())));
dati.addProperty("Provincia", lblProvincia.getText());
dati.addProperty("Data di nascita", fieldDDN.getText());
jsonObject.add(codfis, dati);
String json = gson.toJson(jsonObject);
try (BufferedReader br = new BufferedReader(new FileReader("CodFisCalcolati.json"));
    BufferedWriter bw = new BufferedWriter(new FileWriter("CodFisCalcolati.json", true))) {
    String jsonString = gson.fromJson(br, JsonElement.class).toString();
    JsonElement jelement = new JsonParser().parse(jsonString);
    JsonObject jobject = jelement.getAsJsonObject();
    jobject.add(codfis, dati);
    String resultingJson = gson.toJson(jelement);
    bw.write(resultingJson);
    bw.close();
} catch (IOException e1) { e1.printStackTrace(); }

But when I use it, it give me this output :

{
    "Example":{
        "Ok":"Ok1",
        "Nice":"Nice1",
        "Hi":"Hi1",
        "Hello":"Hello1",
        "Right":"Right1",
        "Wow":"Wow1"
    }
}{
    "Example":{
        "Ok":"Ok1",
        "Nice":"Nice1",
        "Hi":"Hi1",
        "Hello":"Hello1",
        "Right":"Right1",
        "Wow":"Wow1"
    },
    "Example1":{
        "Ok":"Ok2",
        "Nice":"Nice2",
        "Hi":"Hi2",
        "Hello":"Hello2",
        "Right":"Right2",
        "Wow":"Wow2"
    }
}

That's output, you see, it'wrong and i don't know how to make the code to give me a different output.

I'm using Gson 2.8.5 and I would rather not change to another library.

Answer 1

You change the question but now the answer to your new question is you use the same file to read and write. That's why you add the data inside ot the file. Change the name of the file that you write and see if you have problems

Answer 2

Please check if "br" is not null.

According to the specification of the method fromJson it returns: an object of type T from the string. Returns null if json is null.

If this is the case than you call on the null toString() method and you get null pointer exception