IndexOutOfBoundsException error happening depending on Android OS version

Question

I am desperatly trying to fix a bug that:

• always happens in my emulator for Android versions 2.2, 2.3
• never happens in emulator android versions 4.*
• never happens in a real device (android 4.*)

It is the following IndexOutOfBoundsException exception:

java.lang.RuntimeException: Unable to start activity
ComponentInfo{<myapppackage>}: java.lang.IndexOutOfBoundsException:
Invalid index 39, size is 0

In my app I am fecthing data from a json file that I am displaying as text. I've isoleted where the bug is coming from, it is when I call this method:

public String getItemValue(int id, String s) {      

    List<JsonItems> list = new ArrayList<JsonItems>();

    try {
        // CONVERT RESPONSE STRING TO JSON ARRAY
        JSONArray ja = new JSONArray(s);

        // ITERATE THROUGH AND RETRIEVE 
        int n = ja.length();            

        for (int i = 0; i < n; i++) {
            // GET INDIVIDUAL JSON OBJECT FROM JSON ARRAY
            JSONObject jo = ja.getJSONObject(i);

            // RETRIEVE EACH JSON OBJECT'S FIELDS
            JsonItems ji = new JsonItems();
            ji.id = jo.getInt("id");
            ji.text= jo.getString("text");
            list.add(ji);

        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return list.get(id).text; 
}

My class JsonItems is very basic:

public class JsonItems{
int id;
String text;
}

Sample from my json file:

[
{"id":0,"text":"some text 0"},
{"id":1,"text":"some text 1"},
{"id":2,"text":"some text 2"}
]

Here is how I process content of my json file into a String

public static String fromJsonFileToString(String fileName, Context c) {
    //JSONArray jArray = null;
    String text = "";
    try {
        InputStream is = c.getAssets().open(fileName);
        int size = is.available();
        byte[] buffer = new byte[size];
        is.read(buffer);
        is.close();
        text = new String(buffer);

    } catch (IOException e) {
        throw new RuntimeException(e);
    }
    return text;

}

Once again I repeat: the IndexOutOfBoundsException NEVER happens on a device with Android 4.* , it only happens when I test the app on emulators with Android 2.*

Any idea where it is coming from?

Thanks

Answer 1

First problem:

You are not reading your input stream correctly. Calling available literally does just that - it returns you the amount of data that is available to be read, when the call is made. This number may, or may not represent the entire content of the file.

Reading material for you:

• How to Read a File in Java.
• Writing and Creating Files

Note that there are helper libraries like Apache Commons IO that make it possible to read file contents in a single line of code (IOUtils.toString(inputStream)). Android doesn't support Java 7 yet but a noteworthy alternative is available in that release, with the Files.readAllLines method. In any case, you can make the below shown changes to your file reading code and it should work better:

public static String fromFileToString(String fileName, Context context) {
    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                context.getAssets().open(fileName)));

        String line = null;
        StringBuilder builder = new StringBuilder(1024);
        while ((line = reader.readLine()) != null) {
            builder.append(line);
        }

        return builder.toString();
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

Second problem:

You do not do any bound check, to make sure that the argument you pass into your 'search' method:

public String getItemValue(int id, String s)

Does not exceed the length of the list of items you eventually calculate:

return list.get(id).text;
//              ^
// -------------
// 'id' could be larger than the list size!

In any case, your current design doesn't at all match what you are really trying to do, aka, to determine the element in the JSON array that has an 'id' field matching what you supply to the method. You need to process the JSON data as a map, in order to be able to do this.

public String getItemValue(int id, String json) {
    if(json == null || json.trim().equals("")) return null;

    Map<Integer, JsonItems> map = new HashMap<Integer, JsonItems>(4);

    try {
        JSONArray ja = new JSONArray(json);

        int n = ja.length();

        for (int i = 0; i < n; i++) {
            JSONObject jo = ja.getJSONObject(i);

            JsonItems ji = new JsonItems();
            ji.id = jo.getInt("id");
            ji.text = jo.getString("text");
            map.put(Integer.valueOf(ji.id, ji);
        }
    } catch(NumberFormatException nfe) {
      throw new IllegalArgumentException("Invalid JSON format");  
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
    
    JsonItems item = map.get(id);
    return item != null ? item.text : null;
}

Some quick notes:

• JsonItems should be called JsonItem, to conform to good Java naming standards
• You should really parse and store your JSON just once, to improve performance
• You are really only using a minimal subset of your JSON data, you could actually determine the matching node within your for loop and directly return its value, without having to use an intermedia Java bean object