Reading JSON from Url java

java json gson wunderground
Jeel Shah picture Jeel Shah · Feb 19, 2013 · Viewed 25.8k times · Source

I am having trouble with parson the JSON from a URL. Below, is the code. 

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.List;
import com.google.gson.Gson;


public class Test_Application {

    /**
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
        Gson gson = new Gson();

        String json = readUrl("http://api.wunderground.com/api/57dd9039b81a9c21/conditions/q/CA/San_Francisco.json");

        Page page = gson.fromJson(json, Page.class);

        System.out.println(page.description);
        System.out.println(page.language);
        System.out.println(page.link);
        System.out.println(page.title);

    }

    private static String readUrl(String urlString) throws Exception {
        BufferedReader reader = null;
        try {
            URL url = new URL(urlString);
            reader = new BufferedReader(new InputStreamReader(url.openStream()));
            StringBuffer buffer = new StringBuffer();
            int read;
            char[] chars = new char[1024];
            while ((read = reader.read(chars)) != -1)
                buffer.append(chars, 0, read); 

            return buffer.toString();
        } finally {
            if (reader != null)
                reader.close();
        }

    }

    static class Page {
        String title;
        String link;
        String description;
        String language;
        List<Item> items;
    }

    static class Item {
        String title;
        String link;
        String description;
    }


}

The output is: 

null
null
null
null

What I think the problem is that, I have an inappropriate class to read the data. Would that be correct?

Thanks

EDIT

The website returns the following: 

{
  "response": {
    "version": "0.1",
    "termsofService": "http://www.wunderground.com/weather/api/d/terms.html",
    "features": {
      "conditions": 1
    }
  },
  "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, 7:08 AM PST",
    "observation_time_rfc822": "Tue, 19 Feb 2013 07:08:18 -0800",
    "observation_epoch": "1361286498",
    "local_time_rfc822": "Tue, 19 Feb 2013 07:08:31 -0800",
    "local_epoch": "1361286511",
    "local_tz_short": "PST",
    "local_tz_long": "America/Los_Angeles",
    "local_tz_offset": "-0800",
    "weather": "Mostly Cloudy",
    "temperature_string": "47.9 F (8.8 C)",
    "temp_f": 47.9,
    "temp_c": 8.8,
    "relative_humidity": "87%",
    "wind_string": "From the SW at 4.0 MPH Gusting to 13.0 MPH",
    "wind_dir": "SW",
    "wind_degrees": 225,
    "wind_mph": 4.0,
    "wind_gust_mph": "13.0",
    "wind_kph": 6.4,
    "wind_gust_kph": "20.9",
    "pressure_mb": "1012",
    "pressure_in": "29.90",
    "pressure_trend": "-",
    "dewpoint_string": "44 F (7 C)",
    "dewpoint_f": 44,
    "dewpoint_c": 7,
    "heat_index_string": "NA",
    "heat_index_f": "NA",
    "heat_index_c": "NA",
    "windchill_string": "46 F (8 C)",
    "windchill_f": "46",
    "windchill_c": "8",
    "feelslike_string": "46 F (8 C)",
    "feelslike_f": "46",
    "feelslike_c": "8",
    "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"
  }
}

Updated code

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.List;
import com.google.gson.Gson;


public class Test_Application {

    /**
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {
        // TODO Auto-generated method stub
        Gson gson = new Gson();

        String json = readUrl("http://api.wunderground.com/api/57dd9039b81a9c21/conditions/q/CA/San_Francisco.json");

        // Page page = gson.fromJson(json, Page.class);
        Response response = gson.fromJson(json, Response.class);

        System.out.println(response.termsOfService);
        System.out.println(response.version);

    }

    private static String readUrl(String urlString) throws Exception {
        BufferedReader reader = null;
        try {
            URL url = new URL(urlString);
            reader = new BufferedReader(new InputStreamReader(url.openStream()));
            StringBuffer buffer = new StringBuffer();
            int read;
            char[] chars = new char[1024];
            while ((read = reader.read(chars)) != -1)
                buffer.append(chars, 0, read); 

            return buffer.toString();
        } finally {
            if (reader != null)
                reader.close();
        }

    }

    static class Response{
        String version;
        String termsOfService;
    }


}

Answer

Aubin picture Aubin · Feb 19, 2013

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}

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