I am trying to retrieve specific fields from a JSON file that is being retrieved from Wunderground.com.
I tried to post the relevant information in this, but couldn't get it formatted correctly. I am trying to retrieve the longitude and latitude, under the "current_observation" section. I am using Gson 2.2.4. This is the code I currently have:
String key = "aaaaaaaaaaaaaaaa";
String sURL = "http://api.wunderground.com/api/" + key + "/conditions/forecast/q/19104.json";
URL url = new URL(sURL);
URLConnection request = (URLConnection) url.openConnection();
request.connect();
JsonParser jp = new JsonParser(); //from gson
JsonElement root = jp.parse(new InputStreamReader((InputStream) request.getContent()));
JsonObject rootobj = root.getAsJsonObject();
JsonElement latitude = rootobj.get("current_observation");
System.out.println(latitude);
This currently gets everything under the "current_observation" tag, and prints it to the screen. I can not figure out how to access anything under that. I saw several posts on here about using a JsonArray, but no matter what I tried, I could not get it to work correctly. So how do I retrieve a specific field from a JSON file? Thank you for any guidance you can give me, and please let me know if I should provide any additional information.
A JsonElement
is a common interface which is subclassed by two important other classes which are JsonArray
or JsonObject
.
Since you are not providing Gson a type to reflect the information from (and fill a corresponding object) you must go by hand. Since "current_observation"
is a dictionary type then it's a JsonObject
and you can do:
JsonObject observation = root.getAsJsonObject().get("current_observation").getAsJsonObject();
At this point you can retrieve specific fields like you were doing previously:
float longitude = observation.get("longitude").getAsFloat();
and so on.
For specific field you may want to provide custom deserializer or serializer. Actually the best solution would be to have your mirrored structure in code repository, eg:
class Observation
{
float latitude;
float longitude;
// other fields you are interested in
}
so that you can provide your own deserializer and do:
Observation observation = gson.fromJson(root.getAsJsonObject().get("current_observation"), Observation.class)
and let Gson do the dirty work.
Now as your current_observation
JSON itself contains some JSON
as well as String
fileds. I will tell you for 1 string feild station_id
and other JSON
field image
.You can use like this :-
JsonParser jp = new JsonParser(); //from gson
JsonElement root = jp.parse(new InputStreamReader((InputStream) request.getContent()));
JsonObject rootobj = root.getAsJsonObject();
JSONObject curObs = (JSONObject)rootobj.get("current_observation");
JSONObject image = (JSONObject)curObs.get("image"); // image is a JSON
String imageUrl= (String)image.get("url"); // get image url
String stationId = (String)curObs.get("station_id"); // get StationId
Similarly you can do for other attributes of JSON
also. Hope this helped.
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