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java - wunderground - Leyendo una respuesta JSON de WeatherUnderground



wunderground weather provider (1)

package test; import java.net.*; import java.io.*; import com.google.gson.*; import com.google.gson.stream.JsonReader; public class TestGson { URL callToApi; //------------------------------------------------------------------------------ public static void main(String[] args) { new TestGson(); } //------------------------------------------------------------------------------ public TestGson(){ try{ sendCallToApi(); readJson(); }catch(IOException e){ e.printStackTrace(); } } //------------------------------------------------------------------------------ public void sendCallToApi(){ try{ callToApi = new URL("http://api.wunderground.com/api" + "/[insert key here]" + "/geolookup/conditions/forecast/q/" + "Australia/" + "Sydney.json"); }catch(MalformedURLException e){ e.printStackTrace(); } } //------------------------------------------------------------------------------ public void readJson() throws IOException{ Gson g = new Gson(); InputStreamReader in = new InputStreamReader(callToApi.openStream()); BufferedReader reader = new BufferedReader(in); String message = "hello"; StringBuffer buf = new StringBuffer(); while(message!=null){ message = reader.readLine(); buf.append(message); } message = buf.toString(); String wdf = g.fromJson(message, String.class); System.out.println(wdf); } //------------------------------------------------------------------------------ }
Este es mi primer intento de analizar JSON usando GSON. Simplemente estoy haciendo una llamada al sitio Weather Underground para pedirles que me envíen el clima de Sydney, Australia.
Sin embargo, recibo múltiples errores:

Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 2 at com.google.gson.Gson.fromJson(Gson.java:806) at com.google.gson.Gson.fromJson(Gson.java:761) at com.google.gson.Gson.fromJson(Gson.java:710) at com.google.gson.Gson.fromJson(Gson.java:682) at test.TestGson.readJson(TestGson.java:49) at test.TestGson.<init>(TestGson.java:19) at test.TestGson.main(TestGson.java:13) Caused by: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 2 at com.google.gson.stream.JsonReader.nextString(JsonReader.java:464) at com.google.gson.internal.bind.TypeAdapters$13.read(TypeAdapters.java:349) at com.google.gson.internal.bind.TypeAdapters$13.read(TypeAdapters.java:337) at com.google.gson.Gson.fromJson(Gson.java:795) ... 6 more

¿Qué está causando esos errores? ¿Cómo realizo la llamada a Weather Underground API para recibir la información meteorológica?

Intenté esto modificando el ejemplo dado en Mykong.com.

JSON Respuesta del Weather Underground

{ "response": { "version": "0.1" ,"termsofService": "http://www.wunderground.com/weather/api/d/terms.html" ,"features": { "geolookup": 1 , "conditions": 1 , "forecast": 1 } } , "location": { "type":"INTLCITY", "country":"SD", "country_iso3166":"SA", "country_name":"Saudi Arabia", "state":"", "city":"Jeddah", "tz_short":"AST", "tz_long":"Asia/Riyadh", "lat":"21.67000008", "lon":"39.15000153", "zip":"00000", "magic":"1", "wmo":"41024", "l":"/q/zmw:00000.1.41024", "requesturl":"global/stations/41024.html", "wuiurl":"http://www.wunderground.com/global/stations/41024.html", "nearby_weather_stations": { "airport": { "station": [ { "city":"Jeddah King Abdul Aziz International Airport", "state":"", "country":"Saudi Arabia", "icao":"OEJN", "lat":"21.70000076", "lon":"39.18333435" }, { "city":"Jeddah", "state":"", "country":"SD", "icao":"OEJN", "lat":"21.67000008", "lon":"39.15000153" }, { "city":"Makkah", "state":"", "country":"SD", "icao":"OEMK", "lat":"21.43000031", "lon":"39.77000046" } ] } , "pws": { "station": [ ] } } } , "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":"Jeddah, Saudi Arabia", "city":"Jeddah", "state":"", "state_name":"Saudi Arabia", "country":"SD", "country_iso3166":"SA", "zip":"00000", "latitude":"21.67000008", "longitude":"39.15000153", "elevation":"12.00000000" }, "observation_location": { "full":"Jeddah, ", "city":"Jeddah", "state":"", "country":"SD", "country_iso3166":"SA", "latitude":"21.67000008", "longitude":"39.15000153", "elevation":"39 ft" }, "estimated": { }, "station_id":"OEJN", "observation_time":"Last Updated on February 12, 9:00 AM AST", "observation_time_rfc822":"Tue, 12 Feb 2013 09:00:00 +0300", "observation_epoch":"1360648800", "local_time_rfc822":"Tue, 12 Feb 2013 09:08:53 +0300", "local_epoch":"1360649333", "local_tz_short":"AST", "local_tz_long":"Asia/Riyadh", "local_tz_offset":"+0300", "weather":"Clear", "temperature_string":"77 F (25 C)", "temp_f":77, "temp_c":25, "relative_humidity":"57%", "wind_string":"From the North at 10 MPH", "wind_dir":"North", "wind_degrees":10, "wind_mph":10, "wind_gust_mph":0, "wind_kph":17, "wind_gust_kph":0, "pressure_mb":"1011", "pressure_in":"29.86", "pressure_trend":"0", "dewpoint_string":"61 F (16 C)", "dewpoint_f":61, "dewpoint_c":16, "heat_index_string":"NA", "heat_index_f":"NA", "heat_index_c":"NA", "windchill_string":"NA", "windchill_f":"NA", "windchill_c":"NA", "feelslike_string":"77 F (25 C)", "feelslike_f":"77", "feelslike_c":"25", "visibility_mi":"N/A", "visibility_km":"N/A", "solarradiation":"", "UV":"-1", "precip_1hr_string":"-9999.00 in (-9999.00 mm)", "precip_1hr_in":"-9999.00", "precip_1hr_metric":"-9999.00", "precip_today_string":"0.00 in (0.0 mm)", "precip_today_in":"0.00", "precip_today_metric":"0.0", "icon":"clear", "icon_url":"http://icons-ak.wxug.com/i/c/k/clear.gif", "forecast_url":"http://www.wunderground.com/global/stations/41024.html", "history_url":"http://www.wunderground.com/history/airport/OEJN/2013/2/12/DailyHistory.html", "ob_url":"http://www.wunderground.com/cgi-bin/findweather/getForecast?query=21.67000008,39.15000153" } , "forecast":{ "txt_forecast": { "date":"3:00 AM AST", "forecastday": [ { "period":0, "icon":"partlycloudy", "icon_url":"http://icons-ak.wxug.com/i/c/k/partlycloudy.gif", "title":"Tuesday", "fcttext":"Clear in the morning, then partly cloudy. High of 84F. Breezy. Winds from the NNW at 10 to 20 mph.", "fcttext_metric":"Clear in the morning, then partly cloudy. High of 29C. Breezy. Winds from the NNW at 15 to 30 km/h.", "pop":"0" } , { "period":1, "icon":"clear", "icon_url":"http://icons-ak.wxug.com/i/c/k/clear.gif", "title":"Tuesday Night", "fcttext":"Clear. Low of 70F. Winds from the NNW at 10 to 15 mph.", "fcttext_metric":"Clear. Low of 21C. Breezy. Winds from the NNW at 15 to 25 km/h.", "pop":"0" } , { "period":2, "icon":"partlycloudy", "icon_url":"http://icons-ak.wxug.com/i/c/k/partlycloudy.gif", "title":"Wednesday", "fcttext":"Clear in the morning, then partly cloudy. High of 88F. Winds from the NNW at 5 to 15 mph.", "fcttext_metric":"Clear in the morning, then partly cloudy. High of 31C. Breezy. Winds from the NNW at 10 to 25 km/h.", "pop":"0" } , { "period":3, "icon":"clear", "icon_url":"http://icons-ak.wxug.com/i/c/k/clear.gif", "title":"Wednesday Night", "fcttext":"Clear in the evening, then partly cloudy. Low of 70F. Winds from the NW at 5 to 15 mph.", "fcttext_metric":"Clear in the evening, then partly cloudy. Low of 21C. Breezy. Winds from the NW at 10 to 25 km/h.", "pop":"0" } , { "period":4, "icon":"partlycloudy", "icon_url":"http://icons-ak.wxug.com/i/c/k/partlycloudy.gif", "title":"Thursday", "fcttext":"Clear in the morning, then partly cloudy. High of 88F. Winds from the North at 5 to 10 mph shifting to the WSW in the afternoon.", "fcttext_metric":"Clear in the morning, then partly cloudy. High of 31C. Winds from the North at 5 to 15 km/h shifting to the WSW in the afternoon.", "pop":"0" } , { "period":5, "icon":"clear", "icon_url":"http://icons-ak.wxug.com/i/c/k/clear.gif", "title":"Thursday Night", "fcttext":"Clear. Low of 73F. Winds from the WNW at 5 to 10 mph.", "fcttext_metric":"Clear. Low of 23C. Winds from the WNW at 5 to 15 km/h.", "pop":"0" } , { "period":6, "icon":"clear", "icon_url":"http://icons-ak.wxug.com/i/c/k/clear.gif", "title":"Friday", "fcttext":"Clear. High of 88F. Winds from the NNE at 5 to 10 mph shifting to the WSW in the afternoon.", "fcttext_metric":"Clear. High of 31C. Winds from the NNE at 5 to 20 km/h shifting to the WSW in the afternoon.", "pop":"0" } , { "period":7, "icon":"clear", "icon_url":"http://icons-ak.wxug.com/i/c/k/clear.gif", "title":"Friday Night", "fcttext":"Clear. Low of 72F. Winds from the NW at 5 to 10 mph.", "fcttext_metric":"Clear. Low of 22C. Winds from the NW at 5 to 15 km/h.", "pop":"0" } ] }, "simpleforecast": { "forecastday": [ {"date":{ "epoch":"1360692000", "pretty":"9:00 PM AST on February 12, 2013", "day":12, "month":2, "year":2013, "yday":42, "hour":21, "min":"00", "sec":0, "isdst":"0", "monthname":"February", "weekday_short":"Tue", "weekday":"Tuesday", "ampm":"PM", "tz_short":"AST", "tz_long":"Asia/Riyadh"}, "period":1, "high": { "fahrenheit":"84", "celsius":"29" }, "low": { "fahrenheit":"70", "celsius":"21" }, "conditions":"Partly Cloudy", "icon":"partlycloudy", "icon_url":"http://icons-ak.wxug.com/i/c/k/partlycloudy.gif", "skyicon":"mostlysunny", "pop":0, "qpf_allday": { "in": 0.00, "mm": 0.0 }, "qpf_day": { "in": 0.00, "mm": 0.0 }, "qpf_night": { "in": 0.00, "mm": 0.0 }, "snow_allday": { "in": 0, "cm": 0 }, "snow_day": { "in": 0, "cm": 0 }, "snow_night": { "in": 0, "cm": 0 }, "maxwind": { "mph": 17, "kph": 27, "dir": "NW", "degrees": 317 }, "avewind": { "mph": 14, "kph": 22, "dir": "NW", "degrees": 324 }, "avehumidity": 52, "maxhumidity": 74, "minhumidity": 43 } , {"date":{ "epoch":"1360778400", "pretty":"9:00 PM AST on February 13, 2013", "day":13, "month":2, "year":2013, "yday":43, "hour":21, "min":"00", "sec":0, "isdst":"0", "monthname":"February", "weekday_short":"Wed", "weekday":"Wednesday", "ampm":"PM", "tz_short":"AST", "tz_long":"Asia/Riyadh"}, "period":2, "high": { "fahrenheit":"88", "celsius":"31" }, "low": { "fahrenheit":"70", "celsius":"21" }, "conditions":"Partly Cloudy", "icon":"partlycloudy", "icon_url":"http://icons-ak.wxug.com/i/c/k/partlycloudy.gif", "skyicon":"partlycloudy", "pop":0, "qpf_allday": { "in": 0.00, "mm": 0.0 }, "qpf_day": { "in": 0.00, "mm": 0.0 }, "qpf_night": { "in": 0.00, "mm": 0.0 }, "snow_allday": { "in": 0, "cm": 0 }, "snow_day": { "in": 0, "cm": 0 }, "snow_night": { "in": 0, "cm": 0 }, "maxwind": { "mph": 14, "kph": 22, "dir": "NW", "degrees": 308 }, "avewind": { "mph": 12, "kph": 19, "dir": "NW", "degrees": 315 }, "avehumidity": 51, "maxhumidity": 75, "minhumidity": 39 } , {"date":{ "epoch":"1360864800", "pretty":"9:00 PM AST on February 14, 2013", "day":14, "month":2, "year":2013, "yday":44, "hour":21, "min":"00", "sec":0, "isdst":"0", "monthname":"February", "weekday_short":"Thu", "weekday":"Thursday", "ampm":"PM", "tz_short":"AST", "tz_long":"Asia/Riyadh"}, "period":3, "high": { "fahrenheit":"88", "celsius":"31" }, "low": { "fahrenheit":"73", "celsius":"23" }, "conditions":"Partly Cloudy", "icon":"partlycloudy", "icon_url":"http://icons-ak.wxug.com/i/c/k/partlycloudy.gif", "skyicon":"mostlysunny", "pop":0, "qpf_allday": { "in": 0.00, "mm": 0.0 }, "qpf_day": { "in": 0.00, "mm": 0.0 }, "qpf_night": { "in": 0.00, "mm": 0.0 }, "snow_allday": { "in": 0, "cm": 0 }, "snow_day": { "in": 0, "cm": 0 }, "snow_night": { "in": 0, "cm": 0 }, "maxwind": { "mph": 9, "kph": 14, "dir": "West", "degrees": 259 }, "avewind": { "mph": 7, "kph": 11, "dir": "WSW", "degrees": 250 }, "avehumidity": 51, "maxhumidity": 69, "minhumidity": 37 } , {"date":{ "epoch":"1360951200", "pretty":"9:00 PM AST on February 15, 2013", "day":15, "month":2, "year":2013, "yday":45, "hour":21, "min":"00", "sec":0, "isdst":"0", "monthname":"February", "weekday_short":"Fri", "weekday":"Friday", "ampm":"PM", "tz_short":"AST", "tz_long":"Asia/Riyadh"}, "period":4, "high": { "fahrenheit":"88", "celsius":"31" }, "low": { "fahrenheit":"72", "celsius":"22" }, "conditions":"Clear", "icon":"clear", "icon_url":"http://icons-ak.wxug.com/i/c/k/clear.gif", "skyicon":"mostlysunny", "pop":0, "qpf_allday": { "in": 0.00, "mm": 0.0 }, "qpf_day": { "in": 0.00, "mm": 0.0 }, "qpf_night": { "in": 0.00, "mm": 0.0 }, "snow_allday": { "in": 0, "cm": 0 }, "snow_day": { "in": 0, "cm": 0 }, "snow_night": { "in": 0, "cm": 0 }, "maxwind": { "mph": 10, "kph": 16, "dir": "WSW", "degrees": 248 }, "avewind": { "mph": 7, "kph": 11, "dir": "WSW", "degrees": 248 }, "avehumidity": 53, "maxhumidity": 60, "minhumidity": 38 } ] } }}null

Parece que no entiendes lo que hace Gson . Es un analizador JSON, específicamente uno que deserializará JSON a un POJO de Java.

En tu código tienes:

String wdf = g.fromJson(message, String.class);

Le está diciendo a Gson que deserialice el JSON a un objeto Java String . No puede hacer eso; su JSON no es un objeto String , es un gran objeto JSON devuelto por Weather Underground. Ya tiene un Java String ( message ) que contiene el texto JSON en sí.

O bien necesitas crear un POJO para deserializar el JSON o elegir las partes del JSON que desees utilizando el analizador de Gson y los objetos / métodos asociados.

Aquí está el comienzo de cómo se vería un POJO (todos los campos públicos sin getters / setters solo para hacer que este ejemplo sea pequeño):

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; }

Luego deserializarías el JSON en una instancia de MyWUPojo con:

MyWUPojo wup = new Gson().fromJson(message,MyWUPojo.class);

Si no desea ir a la ruta POJO, puede analizar el JSON y obtener lo que quiere de él:

JsonObject o = (JsonObject) new JsonParser().parse(message);

Ahora puede usar los diversos métodos de JsonObject para acceder al JSON analizado. (Ver: http://google-gson.googlecode.com/svn/trunk/gson/docs/javadocs/com/google/gson/JsonObject.html )

La Guía del usuario GSON está muy bien escrita y explica esto y más en gran detalle.

Editar para agregar: ese null al final de su JSON es causado por esto:

while(message!=null){ message = reader.readLine(); buf.append(message); }

Usted agrega null luego sale el bucle. Necesita ser:

while ((message = reader.readline()) != null) { buf.append(message); }