Reading from a Json file and copying the data into a list

January 2, 2023

I would like to read from a json file like:

{
   "name": "Luis Lopez",
   "name": "Armando Guascogne Ursular",
   "name": "Brancar Diego"
}

read from the json file and copy the names into an array list. I tried like this:

public List getName() {
        try {
            Object obj = parser.parse(new FileReader("mypath\name.json"));
            JSONObject jsonObject = (JSONObject) obj;
            String name = (String) jsonObject.get("name");
            for (int i = 0; i<jsonObject.length();i++){
                datasource.add(name);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return datasource;
}

But it returns me the empty list.

>Solution :

First of all, your JSON is not valid, as you’re using the same key name 3 times. This will give you in any case only the last key, Brancar Diego as response in general.

So, you have to do two things:

restructure your JSON
adapt your code (if required)

A JSON restructure could look like so:

{
"names": ["Luis Lopez", "Armando Guascogne Ursular", "Brancar Diego"]
}

In other words, your JSON must contain unique elements, with the above example you’d define a JSON array correctly, which then could be iterated over.

Afterwards, you’d have to adapt your Java Code accordingly.

public List<String> getName() {
    List<String> names = new ArrayList<>();
    try {
        Object obj = parser.parse(new FileReader("mypath\name.json"));
        JSONObject jsonObject = (JSONObject) obj;
        JSONArray nameArray = (JSONArray) jsonObject.get("names");
        for (int i = 0; i < nameArray.length(); i++) {
            names.add((String) nameArray.get(i));
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return names;
}

If you, for whatever reason are not able to change the JSON, you should instead cache each iteration with a unique ID, create a new ArrayList element with these IDs or just populate they keys by Auto Increment and iterate over it again after you’ve formatted it, but that’d be a performance decrease + bad practice + hard to maintain, so I’d not really recommend it.