AsyncTask

AsyncTask

    public class FetchWeatherTask extends AsyncTask<String, Void, String[]> {

        private final String LOG_TAG = FetchWeatherTask.class.getSimpleName();

        /* The date/time conversion code is going to be moved outside the asynctask later,
         * so for convenience we're breaking it out into its own method now.
         */
        private String getReadableDateString(long time) {
            // Because the API returns a unix timestamp (measured in seconds),
            // it must be converted to milliseconds in order to be converted to valid date.
            SimpleDateFormat shortenedDateFormat = new SimpleDateFormat("EEE MMM dd");
            return shortenedDateFormat.format(time);
        }

        /**
         * Prepare the weather high/lows for presentation.
         */
        private String formatHighLows(double high, double low) {
            // For presentation, assume the user doesn't care about tenths of a degree.
            long roundedHigh = Math.round(high);
            long roundedLow = Math.round(low);

            String highLowStr = roundedHigh + "/" + roundedLow;
            return highLowStr;
        }

        /**
         * Take the String representing the complete forecast in JSON Format and
         * pull out the data we need to construct the Strings needed for the wireframes.
         * <p/>
         * Fortunately parsing is easy:  constructor takes the JSON string and converts it
         * into an Object hierarchy for us.
         */
        private String[] getWeatherDataFromJson(String forecastJsonStr, int numDays)
                throws JSONException {

            // These are the names of the JSON objects that need to be extracted.
            final String OWM_LIST = "list";
            final String OWM_WEATHER = "weather";
            final String OWM_TEMPERATURE = "temp";
            final String OWM_MAX = "max";
            final String OWM_MIN = "min";
            final String OWM_DESCRIPTION = "main";

            JSONObject forecastJson = new JSONObject(forecastJsonStr);
            JSONArray weatherArray = forecastJson.getJSONArray(OWM_LIST);

            // OWM returns daily forecasts based upon the local time of the city that is being
            // asked for, which means that we need to know the GMT offset to translate this data
            // properly.

            // Since this data is also sent in-order and the first day is always the
            // current day, we're going to take advantage of that to get a nice
            // normalized UTC date for all of our weather.

            Time dayTime = new Time();
            dayTime.setToNow();

            // we start at the day returned by local time. Otherwise this is a mess.
            int julianStartDay = Time.getJulianDay(System.currentTimeMillis(), dayTime.gmtoff);

            // now we work exclusively in UTC
            dayTime = new Time();

            String[] resultStrs = new String[numDays];
            for (int i = 0; i < weatherArray.length(); i++) {
                // For now, using the format "Day, description, hi/low"
                String day;
                String description;
                String highAndLow;

                // Get the JSON object representing the day
                JSONObject dayForecast = weatherArray.getJSONObject(i);

                // The date/time is returned as a long.  We need to convert that
                // into something human-readable, since most people won't read "1400356800" as
                // "this saturday".
                long dateTime;
                // Cheating to convert this to UTC time, which is what we want anyhow
                dateTime = dayTime.setJulianDay(julianStartDay + i);
                day = getReadableDateString(dateTime);

                // description is in a child array called "weather", which is 1 element long.
                JSONObject weatherObject = dayForecast.getJSONArray(OWM_WEATHER).getJSONObject(0);
                description = weatherObject.getString(OWM_DESCRIPTION);

                // Temperatures are in a child object called "temp".  Try not to name variables
                // "temp" when working with temperature.  It confuses everybody.
                JSONObject temperatureObject = dayForecast.getJSONObject(OWM_TEMPERATURE);
                double high = temperatureObject.getDouble(OWM_MAX);
                double low = temperatureObject.getDouble(OWM_MIN);

                highAndLow = formatHighLows(high, low);
                resultStrs[i] = day + " - " + description + " - " + highAndLow;
            }

            for (String s : resultStrs) {
                Log.v(LOG_TAG, "Forecast entry: " + s);
            }
            return resultStrs;

        }

        @Override
        protected String[] doInBackground(String... params) {

            if (params.length==0)
            {
                return null;
            }
            // These two need to be declared outside the try/catch
            // so that they can be closed in the finally block.
            HttpURLConnection urlConnection = null;
            BufferedReader reader = null;

            // Will contain the raw JSON response as a string.
            String forecastJsonStr = null;

            String format = "json";
            String units = "metric";
            int numDays = 7;

            try {
                // Construct the URL for the OpenWeatherMap query
                // Possible parameters are avaiable at OWM's forecast API page, at
                // http://openweathermap.org/API#forecast
                URL url = new URL("http://api.openweathermap.org/data/2.5/forecast/daily?q=94043&mode=json&units=metric&cnt=7");

                final String FORECAST_BASE_URL =
                        "http://api.openweathermap.org/data/2.5/forecast/daily?";
                final String QUERY_PARAM = "q";
                final String FORMAT_PARAM = "mode";
                final String UNITS_PARAM = "units";
                final String DAYS_PARAM = "cnt";

                Uri builtUri = Uri.parse(FORECAST_BASE_URL).buildUpon()
                        .appendQueryParameter(QUERY_PARAM, params[0])
                        .appendQueryParameter(FORMAT_PARAM, format)
                        .appendQueryParameter(UNITS_PARAM, units)
                        .appendQueryParameter(DAYS_PARAM, Integer.toString(numDays))
                        .build();

                url = new URL(builtUri.toString());

                Log.v(LOG_TAG, "Built URI " + builtUri.toString());

                // Create the request to OpenWeatherMap, and open the connection
                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.connect();

                // Read the input stream into a String
                InputStream inputStream = urlConnection.getInputStream();
                StringBuffer buffer = new StringBuffer();
                if (inputStream == null) {
                    // Nothing to do.
                    return null;
                }
                reader = new BufferedReader(new InputStreamReader(inputStream));

                String line;
                while ((line = reader.readLine()) != null) {
                    // Since it's JSON, adding a newline isn't necessary (it won't affect parsing
                    // But it does make debugging a *lot* easier if you print out the completed
                    // buffer for debugging
                    buffer.append(line + "\n");
                }

                if (buffer.length() == 0) {
                    // Stream was empty.  No point in parsing.
                    return null;
                }
                forecastJsonStr = buffer.toString();
            } catch (IOException e) {
                Log.e(LOG_TAG, "Error ", e);
                // If the code didn't successfully get the weather data, there's no point in attemping
                // to parse it.
                return null;
            } finally {
                if (urlConnection != null) {
                    urlConnection.disconnect();
                }
                if (reader != null) {
                    try {
                        reader.close();
                    } catch (final IOException e) {
                        Log.e(LOG_TAG, "Error closing stream", e);
                    }
                }
            }
            try {
                return getWeatherDataFromJson(forecastJsonStr,numDays);
            }catch (JSONException e)
            {
                Log.e(LOG_TAG,e.getMessage(),e);
                e.printStackTrace();
            }
            return null;
        }
        @Override
        protected void onPostExecute(String [] result) {
            super.onPostExecute(result);
            if (result != null) {
                forecastAdapter.clear();
                for(String dayForecastStr : result) {
                    forecastAdapter.add(dayForecastStr);
                }
                // New data is back from the server.  Hooray!
            }
        }
    }