Question

I am trying to parse json object to populate it into list view,but i am facing some problem please help

I am getting NullpointerException

here is my full code:

I am parsing data from the following url

URL I AM PARSING IS

code for parsing data

 public class JSONParser {

static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

public JSONParser(){

}

public JSONObject getJSONFromUrl(String url){

//making Http request
try{
//default httpclient    
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);

HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
is = httpEntity.getContent();

}
    catch (UnsupportedEncodingException e) {
    e.printStackTrace();
    }
catch (ClientProtocolException e) {
    e.printStackTrace();

}
catch(IOException e){
    e.printStackTrace();
    }
    try{
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);

        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
    } 
catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    // return JSON String
    return jObj;

}

}

here is activity code

public class AndroidJSONParsingActivity extends ListActivity {

// url to make request
private static String url = "http://www.kaverisoft.com/careers/assignments/android/a1.php";

// JSON NAme Node

private static final String TAG_BOOK = "book";
private static final String TAG_ID = "id";
private static final String TAG_TITLE = "title";
private static final String TAG_AUTHORS = "authors";
private static final String TAG_DESCRIPTION = "description";
private static final String TAG_PRICE = "price";


//Book JSONArray
JSONArray book = null;

@Override
public void onCreate(Bundle savedInstanceState) {


    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // HashMap for ListView

    ArrayList<HashMap<String, String>> bookList = new ArrayList<HashMap<String, String>>();

    // creating Json parser instance
    JSONParser jParser = new JSONParser();

    // getting Json String from url

    JSONObject json = jParser.getJSONFromUrl(url);

    try{
        // getting array of books

        book = json.getJSONArray(TAG_BOOK);

    // looping through all books

        for(int i=0;i<book.length();i++){

            JSONObject c = book.getJSONObject(i);


            // storing each json item in variable

            String title = c.getString(TAG_TITLE);
            String price = c.getString(TAG_PRICE);
            String authors = c.getString(TAG_AUTHORS);
            String id = c.getString(TAG_ID);
            String description = c.getString(TAG_DESCRIPTION);



            // creating new HashMap
            HashMap<String, String> map = new HashMap<String, String>();

            map.put(TAG_ID, id);
            map.put(TAG_TITLE, title);
            map.put(TAG_PRICE, price);
            map.put(TAG_AUTHORS, authors);
            map.put(TAG_DESCRIPTION, description);

            bookList.add(map);


        }

    }

        catch (JSONException e) {
            e.printStackTrace();    

        }

    // Updating Parsed Data into ListView

    ListAdapter adapter = new SimpleAdapter(this, bookList,
            R.layout.list_item,
            new String[]{TAG_TITLE,TAG_DESCRIPTION,TAG_AUTHORS } , new int[] {
            R.id.title,R.id.description,R.id.author });

setListAdapter(adapter);

// selecting single list view item

ListView lv = getListView();

 // Launching new screen on Selecting Single ListItem
    lv.setOnItemClickListener(new OnItemClickListener() {


        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                int position, long id) {
            // getting values from selected ListItem
            String title = ((TextView) view.findViewById(R.id.title)).getText().toString();
            String authors = ((TextView) view.findViewById(R.id.author)).getText().toString();
            String description = ((TextView) view.findViewById(R.id.description)).getText().toString();

            // Starting new intent
            Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class);
            in.putExtra(TAG_TITLE, title);
            in.putExtra(TAG_AUTHORS, authors);
            in.putExtra(TAG_DESCRIPTION, description);
            startActivity(in);

        }
    });



}

}

I am trying to parse only book object

Please solve my problem.

LogCat detail’s

08-24 00:56:48.202: W/dalvikvm(949): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
08-24 00:56:48.263: E/AndroidRuntime(949): FATAL EXCEPTION: main
08-24 00:56:48.263: E/AndroidRuntime(949): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sree.androidjsonparser/com.sree.androidjsonparser.AndroidJSONParsingActivity}: java.lang.NullPointerException
08-24 00:56:48.263: E/AndroidRuntime(949):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
08-24 00:56:48.263: E/AndroidRuntime(949):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
08-24 00:56:48.263: E/AndroidRuntime(949):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
08-24 00:56:48.263: E/AndroidRuntime(949):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
08-24 00:56:48.263: E/AndroidRuntime(949):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-24 00:56:48.263: E/AndroidRuntime(949):  at android.os.Looper.loop(Looper.java:123)
08-24 00:56:48.263: E/AndroidRuntime(949):  at android.app.ActivityThread.main(ActivityThread.java:4627)
08-24 00:56:48.263: E/AndroidRuntime(949):  at java.lang.reflect.Method.invokeNative(Native Method)
08-24 00:56:48.263: E/AndroidRuntime(949):  at java.lang.reflect.Method.invoke(Method.java:521)
08-24 00:56:48.263: E/AndroidRuntime(949):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-24 00:56:48.263: E/AndroidRuntime(949):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-24 00:56:48.263: E/AndroidRuntime(949):  at dalvik.system.NativeStart.main(Native Method)
08-24 00:56:48.263: E/AndroidRuntime(949): Caused by: java.lang.NullPointerException
08-24 00:56:48.263: E/AndroidRuntime(949):  at com.sree.androidjsonparser.AndroidJSONParsingActivity.onCreate(AndroidJSONParsingActivity.java:62)
08-24 00:56:48.263: E/AndroidRuntime(949):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-24 00:56:48.263: E/AndroidRuntime(949):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
08-24 00:56:48.263: E/AndroidRuntime(949):  ... 11 more
08-24 00:56:53.812: I/Process(949): Sending signal. PID: 949 SIG: 9

Answer 1

Your issue is with your JSONParser..that and the JSON returned from the site isnt well formed. You have a bunch of JSONObjects with JSONObjects inside of them that have similar names. I made a quick and easy solution to deal with it but if you control the code that generates the JSON then I would suggest grouping the categories of items (books, music, camera) into their own JSONArrays

The JSON you’re getting back from the website is a JSONArray with JSONObjects.. you’re doing the following

jObj = new JSONObject(json);

You should be doing

jObj = new JSONArray(json);

Then you need to change your return to be a JSONArray instead of JSONObject

Then in the main activity change “json” to JSONArray and get rid of “book”..just loop through the JSONArray

Also move your try to be inside of the loop.

JSONParser jParser = new JSONParser();

            // getting Json String from url

            JSONArray json = jParser.getJSONFromUrl(url);


                // getting array of books

               //Get rid of this = book = json.getJSONArray(TAG_BOOK);

            // looping through all books

                 for(int i=0;i<json.length();i++){
                try{
                JSONObject parent = json.getJSONObject(i);
                JSONObject c  = parent.optJSONObject("camera");
                if(c == null)
                    c = parent.optJSONObject("book");
                if(c == null)
                    c = parent.optJSONObject("music");
                // storing each json item in variable

                String title = c.getString(TAG_TITLE);
                String price = c.getString(TAG_PRICE);
                String authors = c.getString(TAG_AUTHORS);
                String id = c.getString(TAG_ID);
                String description = c.getString(TAG_DESCRIPTION);
                // creating new HashMap
                HashMap<String, String> map = new HashMap<String, String>();

                map.put(TAG_ID, id);
                map.put(TAG_TITLE, title);
                map.put(TAG_PRICE, price);
                map.put(TAG_AUTHORS, authors);
                map.put(TAG_DESCRIPTION, description);

                bookList.add(map);

            }

            catch (JSONException e) {
                e.printStackTrace();    

            }
            }

—–EDIT

As suggested in my comment, you should redo the code that creates the JSON output

In simple terms, you need a master array that contains JSONObjects for each “category”, and then each of those categories will be a JSONObject in a JSONArray

The JSON should look like this

[
{ "camera" :
[
   {
   "picture":"http://qqq.com",
   "price":9.99
    },
 {
   "picture":"http://eee.com",
   "price":9.99
    }
]
},
{ "music" :
[
   {
   "picture":"http://aaa.com",
   "price":9.99
    },
 {
   "picture":"http://sss.com",
   "price":9.99
    }
]
},
{ "book" :
[
   {
   "picture":"http://fff.com",
   "price":9.99
    },
 {
   "picture":"http://ggg.com",
   "price":9.99
    }
]
}
]

This way you can do different actions (if needed) for the different categories and have any similar JSON Objects in the category all grouped together.

Or if the action will be the same regardless if it’s a book, music or camera then you can just add another field to your JSON Objects for “type” and then create the JSONObject in the array (JSON_array.put()) without a name so it would appear as

[
{
"type":"camera",
"picture":"http://img5.flixcart.com/image/camera/5/p/a/nikon-d90-slr-40x40-imacxmh3y6wmqh8b.jpeg",
"model":"D90 SLR with AF-S 18-105mm VR Kit Lens",
"make":"Nikon",
"price":57182.0
},
{
"type":"book",
"description":"This book is one of a series of texts written by faculty of the Electrical Engineering and Computer Science Department at the Massachusetts Institute of Technology. It was edited and produced by The MIT Press under a joint production-distribution arrangement with the McGraw-Hill Book Company.",
"authors":"Harold Abelson and Gerald Jay Sussman with Julie Sussman",
"price":469.0,
"id":51087,
"title":"Structure and Interpretation of Computer Programs"
}
]

Again, the route you should take depends on what you’ll be doing with the data afterwards