Android JSON Web服务

Question

I am working on web services that I want from my Android application connect to Oracle database, so my server is in java which connects to database... and the connection is done! What I am stuck to is that I got data from database and converted to json in the server side when I retrieve it in my Android app there I get null pointer exception.

Function to create my json in server side:

public static String constructJSN(String tag, boolean status,ArrayList<Teacher> f) {

JSONObject obj = new JSONObject();
try {
    for(int i=0;i<f.size();i++){
    obj.put("tag", tag);
    obj.put("status", new Boolean(status));
    String json = new Gson().toJson(f);
    obj.put("data",json);
    }


} catch (JSONException e) {
    // TODO Auto-generated catch block
}
return obj.toString(); 
}

and when i print it i get :

{"tag":"login","status":true,"data":"[{\"name\":\"rasha\",\"classes\":\"b\",\"freetime\":\"3-4\"},{\"name\":\"heba\",\"classes\":\"a\",\"freetime\":\"3-4\"},{\"name\":\"omnia\",\"classes\":\"c\",\"freetime\":\"2-6\"}]"}

in android client side :

                   String j= obj.get("data").toString();
                  JSONObject myJsonObj = new JSONObject(j);
                  String Name = myJsonObj.getString("name");
                    String Classes = myJsonObj.getString("classes");
                    Toast.makeText(getApplicationContext(), Name+ " " + Classes, Toast.LENGTH_LONG).show();

and here I get an error while debugging:

Method threw java.lang.NullPointerException exception. Cannot evaluate org.json.JSONObject.toString()

Answer 1

JSONObject myJsonObj = new JSONObject(j);
JsonArray data = myJsonObj.getJsonArray("data");
for (JSONObject jObjc: JsonArray) { 
 String Classes = jObjc.getString("classes");
}

Answer 2

Try the below:

Declare a static JsonObject and assign it to null static JSONObject jObj = null;

Then in ur web service call, assign this to the JSON Response like this jObj = new JSONObject(result);

jObj.getString("data");