RESTful request using HTTPUrlConnection-Collection of common programming errors

I’m writing my first Android app, and trying to get the hang of making a REST call from within the app. Following a couple pages and other SO posts, I’ve got this:

URL serverUrl = new URL("http://localhost:13980/api/maps/"); //the value is hardcoded for testing purposes

public String getMapsJson()
{
    Log.d("Minimap", ">> getting maps json from " + serverUrl.toString());
    String output = "";

    HttpURLConnection connection = null;

    try
    {
        connection = (HttpURLConnection) serverUrl.openConnection();
        connection.setRequestMethod("GET");
        Log.d("Minimap", "connection opened!");
        InputStream in = new BufferedInputStream(connection.getInputStream());
        Log.d("Minimap", "input stream captured");
        output = readStream(in);
        Log.d("Minimap", "stream read");
    }

    catch (Exception e)
    {
        Log.d("Minimap", e.getMessage()); //************* This is line 53