Exploring the automated retrieval of data from arrays in Java objects: A comprehensive guide

My goal is to automatically create Java objects from JSON data obtained from a REST API. The JSON array contains properties of different shops, and I aim to generate one object per shop with all its respective properties.

The following code helped me achieve this:

ArrayList<Magasin> objMag= new ArrayList<Magasin>();
                JSONArray databrute = new JSONArray(sortie);
                for (int i = 0; i < databrute.length(); i++){
                    ville = databrute.getJSONObject(i).getString("ville");
                    nom = databrute.getJSONObject(i).getString("nom");
                    objMag.add(new Magasin(ville,nom/*,rue,type,descrp,createur,statutlegal,datecreat,datemodif,magcreat,codepost,id,nbemployes,turnover1,turnover2*/));
                }
                System.out.println(objMag.get(2).getVille);

            }

If we consider the following (long) JSON dataset:

[
// JSON data
]

I anticipated having 4 generated objects ([Magasin@1d81eb93, Magasin@7291c18f, Magasin@34a245ab, Magasin@7cc355be]) when printing the objMag array. However, when trying to access specific data from an object like Magasin@34a245ab using 

System.out.println(objMag.get(2).getVille);
, it always returns data from Magasin@1d81eb93. How can I access data from the other objects? Is there an issue with how I'm generating these objects?

javaarraysjsonarraylist

Answer №1

To quickly resolve your issue, using org.apache.commons.io.IOUtils along with com.fasterxml.jackson.databind.ObjectMapper is recommended.

Consider the following code snippet:

class MegaSinList{
    private List<MegaSin> megasinList;
}

class MegaSin{
    private String codePostale;
    private String createur;
    private String creationDate;
    private String creationShop;
    private String description;
    private int identifiant;
    private String modification;
    private String nom;
    private int nombreEmploye;
    private String rue;
    private String statutLegal;
    private long turnOverRange1;
    private long turnOverRange2;
    private String type;
    private String ville;
}

and utilize the function below to extract data:

byte[] jsonData = IOUtils.toByteArray("/...filepath../file.json").getInputStream());
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
MegaSinList magasinListObj = objectMapper.readValue(jsonData, MegaSinList.class);
return magasinListObj;

Keep in mind that depending on the json structure, ObjectMapper may return a list of LinkedHashMap containing key-value pairs. In such cases, you may need to retrieve data using map.get("key") from the list and assign it to the desired object.

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