How to parse json to class objects in java?

Assuming you have a POJO like the following

public class Persona {

    private String nombre;

    private String edad;

    //getters
    //setters
}

You could use ObjectMapper

ObjectMapper mapper = new ObjectMapper();

String respuesta = "{"nombre": "nombre", "edad": 99}";
Persona persona = mapper.readValue(respuesta, Persona.class);

String respuesta = "[{"nombre": "nombre", "edad": 99}]";
List<Persona> personas = mapper.readValue(respuesta, new TypeReference<List<Persona>>(){});

Good morning,

I for the treatment of json use com.fasterxml.jackson .

In your case, the POJO would be as follows:

import com.fasterxml.jackson.annotation.JsonProperty;

public class BockChapter {

    @JsonProperty(value = "Numbre")
    private int number;

    @JsonProperty(value = "Title")
    private String title;

    @JsonProperty(value = "Pages")
    private int pages;

    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public int getPages() {
        return pages;
    }

    public void setPages(int pages) {
        this.pages = pages;
    }

    @Override
    public String toString() {
        return "Libro [number=" + number + ", title=" + title + ", pages=" + pages + "]";
    }   
}

I added the @JsonProperty annotation so that the names of the fields meet the standards in java.

The code for parsing the response in an array of objects is as follows:

String response = "[{\"Numbre\":1,\"Title\":\"Hola Mundo1\",\"Pages\":222},{\"Numbre\":2,\"Title\":\"Hola Mundo2\",\"Pages\":222},{\"Numbre\":3,\"Title\":\"Hola Mundo3\",\"Pages\":222}]";

        ObjectMapper mapper = new ObjectMapper();

        try {
            List<BockChapter> libros = mapper.readValue(response, mapper.getTypeFactory().constructCollectionType(List.class, BockChapter.class));
            System.out.println(libros);
        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

In this case, being a list, we have to specify the type of collection to which we want to parse the answer.

I hope this helps you.

Greetings

The error indicates that what you are getting is an Array (JSONArray) and that can not be converted to JSONObject. So try to convert it to JSONArray and handle the information with the methods that that class provides you. You can try what is mentioned here and maybe see more information:

JSONParser parser = new JSONParser();
Object obj  = parser.parse(content);
JSONArray array = new JSONArray();
array.add(obj);

One way to obtain the data would be as follows:

Librería Gson:

compile 'com.google.code.gson:gson:2.7'

Github: link

Documentation: link

*
 //Json de tu web service
        String json = "[{\"Numbre\":1,\"Title\":\"Hola Mundo1\",\"Pages\":222},{\"Numbre\":2,\"Title\":\"Hola Mundo2\",\"Pages\":222},{\"Numbre\":3,\"Title\":\"Hola Mundo3\",\"Pages\":222},{\"Numbre\":4,\"Title\":\"Hola Mundo4\",\"Pages\":222},{\"Numbre\":5,\"Title\":\"Hola Mundo5\",\"Pages\":222},{\"Numbre\":6,\"Title\":\"Hola Mundo6\",\"Pages\":222},{\"Numbre\":7,\"Title\":\"Hola Mundo7\",\"Pages\":222},{\"Numbre\":8,\"Title\":\"Hola Mundo8\",\"Pages\":222}]";




//Json parser | JsonElements
        JsonParser jsonParser = new JsonParser();
        //Parsear el json string a JsonObject, a JsonArray, a JsonPrimitive o a JsonNull
        JsonElement element = jsonParser.parse(json);
        //verificamos si es un json array
        if (element.isJsonArray())
        {
            //parseamos el elemento a json array
            JsonArray jsonArray = element.getAsJsonArray();
            //lista de tipo objeto para almacenar tus valores
            List<BockChapter> bockChapters = new ArrayList<>();
            //recorremos el json array
            for (int i=0;i<jsonArray.size();i++)
            {
                //obtenemos los objetos de la posición i
                JsonObject  objectJ = jsonArray.get(i).getAsJsonObject();
                //modelo para asignar tus valores
                BockChapter object = new BockChapter();
                //Obtenemos los valores
                object.setNumber(objectJ.get("Numbre").getAsString());
                object.setTitle(objectJ.get("Title").getAsString());
                object.setPages(objectJ.get("Pages").getAsInt());
                //agregamos a la lista
                bockChapters.add(object);
            }
            //verificamos la cantidad de registros obtenidos y agregados a la lista
            Log.e("List<BockChapter>: ","=> "+ bockChapters.size());
        }

Or:

try {
            //Recibimos el JSON Array
            JSONArray array = new JSONArray(json);
            //Recorremos el Array
            for (int i = 0; i <array.length(); i++)
            {
                //Obtenermos los objetos de la posición i
                JSONObject object = array.getJSONObject(i);
                BockChapter bockChapter = new BockChapter();
                //Obtenemos los valores del objeto en la posición indicada
                bockChapter.setNumber(object.getString("Numbre"));
                bockChapter.setTitle(object.getString("Title"));
                bockChapter.setPages(object.getInt("Pages"));
            }
        }catch (Exception e){
            e.printStackTrace();
        }

How to identify a JSONArray of a JSONObject? I leave the following image to you to detect when it is a JSON array or a JSON object.