Reading JSON from Url java [closed]

Question 1

Alternatives to GSON exists:

This snippet may help to do a generic decoder:

Map< String, Object > decoded =
   gson.fromJson(data, new TypeToken< Map< String, Object>>() {}.getType());

The following code is a beginning of a specific decoder:

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;

import com.google.gson.Gson;

public class Test_Application
{
   public static void main(
      String[] args ) throws Exception
   {
      Gson gson = new Gson();
      String json = readUrl(
         "http://api.wunderground.com/api/57dd9039b81a9c21/" +
         "conditions/q/CA/San_Francisco.json" );
      System.out.println( json );

      Map< String, Object > decoded =
         gson.fromJson(
            json,
            new TypeToken< Map< String, Object>>() {}.getType());
      System.out.println( decoded );

      Answer answer = gson.fromJson( json, Answer.class );
      System.out.println( answer.response.version );
      System.out.println( answer.response.termsofService );
      System.out.println( answer.response.features.get( "conditions" ));
      System.out.println( answer.current_observation.image );
      System.out.println( answer.current_observation.display_location );
   }

   static class Response
   {
      String                version;
      URL                   termsofService;
      Map< String, String > features;
   }

   static class Observation
   {
      Map< String, String > image;
      Map< String, String > display_location;
      // TODO: complete me
   }

   static class Location
   {
      // TODO: complete me
   }

   static class Answer
   {
      Response    response;
      Observation current_observation;
      Location    display_location;
      // TODO: complete me
   }

At this state of development, it returns:

{response={version=0.1, termsofService=http://www.wunderground.com/weather/api/d/terms.html, features={conditions=1.0}}, current_observation={image={url=http://icons-ak.wxug.com/graphics/wu2/logo_130x80.png, title=Weather Underground, link=http://www.wunderground.com}, display_location={full=San Francisco, CA, city=San Francisco, state=CA, state_name=California, country=US, country_iso3166=US, zip=94101, latitude=37.77500916, longitude=-122.41825867, elevation=47.00000000}, observation_location={full=SOMA - Near Van Ness, San Francisco, California, city=SOMA - Near Van Ness, San Francisco, state=California, country=US, country_iso3166=US, latitude=37.773285, longitude=-122.417725, elevation=49 ft}, estimated={}, station_id=KCASANFR58, observation_time=Last Updated on February 19, 8:16 AM PST, observation_time_rfc822=Tue, 19 Feb 2013 08:16:18 -0800, observation_epoch=1361290578, local_time_rfc822=Tue, 19 Feb 2013 08:16:18 -0800, local_epoch=1361290578, local_tz_short=PST, local_tz_long=America/Los_Angeles, local_tz_offset=-0800, weather=Mostly Cloudy, temperature_string=48.7 F (9.3 C), temp_f=48.7, temp_c=9.3, relative_humidity=83%, wind_string=From the ESE at 1.0 MPH, wind_dir=ESE, wind_degrees=109.0, wind_mph=1.0, wind_gust_mph=0.0, wind_kph=1.6, wind_gust_kph=0.0, pressure_mb=1012, pressure_in=29.88, pressure_trend=-, dewpoint_string=44 F (7 C), dewpoint_f=44.0, dewpoint_c=7.0, heat_index_string=NA, heat_index_f=NA, heat_index_c=NA, windchill_string=49 F (9 C), windchill_f=49, windchill_c=9, feelslike_string=49 F (9 C), feelslike_f=49, feelslike_c=9, visibility_mi=10.0, visibility_km=16.1, solarradiation=, UV=0, precip_1hr_string=0.00 in ( 0 mm), precip_1hr_in=0.00, precip_1hr_metric= 0, precip_today_string=0.02 in (1 mm), precip_today_in=0.02, precip_today_metric=1, icon=mostlycloudy, icon_url=http://icons-ak.wxug.com/i/c/k/mostlycloudy.gif, forecast_url=http://www.wunderground.com/US/CA/San_Francisco.html, history_url=http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=KCASANFR58, ob_url=http://www.wunderground.com/cgi-bin/findweather/getForecast?query=37.773285,-122.417725}}

0.1
http://www.wunderground.com/weather/api/d/terms.html
1
{url=http://icons-ak.wxug.com/graphics/wu2/logo_130x80.png, title=Weather Underground, link=http://www.wunderground.com}
{full=San Francisco, CA, city=San Francisco, state=CA, state_name=California, country=US, country_iso3166=US, zip=94101, latitude=37.77500916, longitude=-122.41825867, elevation=47.00000000}

Question 2

Your problem is that your POJO doesn't match your JSON.

JSON represents an object, and your POJO needs to match it. Here's a start of what that would look like (all fields public with no getters/setters just to make this example small):

class MyWUPojo {
    public Response response;
    // more after this that match the JSON
}

class Response {
    public String version;
    public String termsofservice;
    public Map<String, Integer> features;
}

Note that the one caveat is that if you are only interested in part of the JSON response, that's all you have to implement. Gson will silently ignore any part of the JSON you haven't included in your POJO.