Reading JSON data using Java

You can use Gson - from Google. It is simple and concise.

You need to declare your Java POJO that represents your JSON data, like:

public class Info {
   private Category category;
   ...
}

Hope this help. Good luck.

write and read this:

[
  {
    "id": 1,
    "firstname": "Bart",
    "lastname": "Simpson",
    "address": {
      "city": "Springfield",
      "country": "USA"
    }
  },
  {
    "id": 2,
    "firstname": "Homer",
    "lastname": "Simpson",
    "address": {
      "city": "Springfield",
      "country": "USA"
    }
  },
  {
    "id": 3,
    "firstname": "Mickey",
    "lastname": "Mouse",
    "address": {
      "city": "Orlando",
      "country": "USA"
    }
  }

PersonJson:

public class PersonJSON {
    private int id;
    private String firstname;
    private String lastname;
    private AddressJSON address;
    
    public PersonJSON(int id, String firstname, String lastname, AddressJSON address)
    {
        this.id = id;
        this.firstname = firstname;
        this.lastname = lastname;
        this.address = address;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getFirstname() {
        return firstname;
    }

    public void setFirstname(String firstname) {
        this.firstname = firstname;
    }

    public String getLastname() {
        return lastname;
    }

    public void setLastname(String lastname) {
        this.lastname = lastname;
    }
    
    public AddressJSON getAddress() {
        return address;
    }

    public void setAddress(AddressJSON address) {
        this.address = address;
    }

    public String toString()
    {
        return "id: " + this.id + " - Firstname: " + this.firstname + " - Lastname: " + this.lastname + ", " + getAddress().toString();
    }
}

AddressJson:

import com.google.gson.annotations.SerializedName;

public class AddressJSON {
    //@SerializedName("Cidade")
    private String city;
    private String country;
    
    public AddressJSON(String city, String country)
    {
        this.city = city;
        this.country = country;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }
    
    @Override
    public String toString(){
        return city + ", " + country;
    }
}

Main:

import java.io.FileReader;
import java.io.FileWriter;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;

public class PDJSON {

    private List<PersonJSON> people;

    public PDJSON() {
        people = new ArrayList<PersonJSON>();
    }

    public void saveData(String filePath) {
        //Gson gson = new Gson();
        Gson gson = new GsonBuilder().setPrettyPrinting().create();
        
        try(FileWriter fw = new FileWriter(filePath)){
            gson.toJson(people, fw);        
        }catch(Exception e)
        {
            e.printStackTrace();
        }
    }

    public List<PersonJSON> loadData(String filePath) {
        Gson gson = new Gson();
        JsonReader jsonReader = null;

        final Type CUS_LIST_TYPE = new TypeToken<List<PersonJSON>>() {}.getType();
        //or TypeToken.getParameterized(ArrayList.class, PersonJSON.class).getType();
        
        try{
            jsonReader = new JsonReader(new FileReader(filePath));
        }catch (Exception e) {
            e.printStackTrace();
        }

        return gson.fromJson(jsonReader, CUS_LIST_TYPE); 
    }

    public static void main(String[] args) {
        PDJSON pdj = new PDJSON();
        pdj.people.add(new PersonJSON(1,"Bart", "Simpson", new AddressJSON("Springfield", "USA")));
        pdj.people.add(new PersonJSON(2,"Homer", "Simpson", new AddressJSON("Springfield", "USA")));
        pdj.people.add(new PersonJSON(3,"Mickey", "Mouse", new AddressJSON("Orlando", "USA")));

        pdj.saveData("resources/listofpeople.json");

        List<PersonJSON> lp = pdj.loadData("resources/listofpeople.json"); 
        for(PersonJSON pj : lp)
        {
            System.out.println(pj.toString());
        }
    }
}