java – Problems with restfull api

Question:

I have a Restfull API on the local Apache server that returns a list of users from the database (localhost/api/users).

I'm using JSONLint site to validate my JSON. When accessing via browser I get the result and validate it in JSONLint, which returns me as valid JSON. An example returned by the API:

{
    "usuarios": [
        {
            "id": 167,
            "contrato": 1,
            "cod": "1212",
            "nome": "Marcos Roberto Pavesi",
            "email": "marcos@p.com.br",
            "senha": "114fdfefd3d69799f0b6f73ef764d405",
            "ativo": "S",
            "setor": "1",
            "max_add": "",
            "dealer": 0
        },
        {
            "id": 520,
            "contrato": 1,
            "cod": "",
            "nome": "avaliador",
            "email": "avaliador@teste.com.br",
            "senha": "e10adc3949ba59abbe56e057f20f883e",
            "ativo": "S",
            "setor": "2",
            "max_add": "",
            "dealer": 0
        }
    ]
}

However, I am trying to access my application via Java following this explanation and I am getting the following error:

Exception in thread "main" org.json.JSONException:
A JSONObject text must begin with '{' at 1 [character 2 line 1]

at org.json.JSONTokener.syntaxError(JSONTokener.java:433)
at org.json.JSONObject.(JSONObject.java:197)
at org.json.JSONObject.(JSONObject.java:324)
at com.main.Main.main(Main.java:14)

I'm accessing the api with the following code…

public static void main(String[] args) {


        JSONObject obj = new JSONObject("http://localhost:8080/api_carmaix/api/usuarios");
        JSONArray arr = null;
        try {
                arr = obj.getJSONArray("usuarios");
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }




            for (int i = 0; i < arr.length(); i++)
            {            
                System.out.println(arr.getJSONObject(i).getString("id")); 

            }
}

}

Answer:

Keep in mind that the classes in this package do not make requests.
They parse some source ( String , Map , …) and allow you to manipulate the object like a JSON.

Your code throws a JSONException because a string starting with " { " is expected and you are passing a url.

You need to break things down: First make the request to get the response from your API — and here it doesn't have to be anything complex, you can get the response as a string anyway. Once you have the answer in hand, you create a JSONObject and pass that string as an argument to the constructor.

You can create a method that fetch the JSON in a url:

public String getJSON(String url){
    String data = null;

    try {
        HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
        connection.setRequestMethod("GET");
        connection.connect();

        if(connection.getResponseCode() == 200){
            try (BufferedReader buff = new BufferedReader(new InputStreamReader(connection.getInputStream()))){
                String line;
                StringBuilder builder = new StringBuilder();

                while((line = buff.readLine()) != null)
                    builder.append(line);
                data = builder.toString();
            }
        }
    } catch(Exception err){
        // Algum tratamento :)
    }
    return data;
}

Having this method, you can call it passing the URL that your API returns the JSON with the users. And the return, you can pass in the JSONObject constructor:

// Resposta da API
String data = getJSON("http://localhost:8080/api_carmaix/api/usuarios");

if (data != null) {
    try {
       // Usando a resposta da API para criar um objeto JSON:
       JSONObject json = new JSONObject(data);

       JSONArray jsonArray = json.getJSONArray("usuarios");
       for (int i = 0; i < jsonArray.length(); i++)
           System.out.println("ID: " + jsonArray.getJSONObject(i).getInt("id"));

    } catch (Exception err) {}
}

Also see that when traversing the JSONArray I used getInt instead of getString as you are using. If you try to get the value of "id" as a string a JSONException will also be thrown containing the message:

JSONObject["id"] not a string.

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