Question

I’m using wunderground to get weather information on my java web application.
After some search I came across Gson which seems like a good json parser.

But following some examples I can’t seem to figure out how to skip root elements.
Here is an example of a forecast json request:

{
    "forecast" : {
        "simpleforecast" : {
            "forecastday" : [ {
                "avehumidity" : 61,
                "avewind" : {
                    "degrees" : 342,
                    "dir" : "NNW",
                    "kph" : 11,
                    "mph" : 7
                },
                "conditions" : "Clear",
                "date" : {
                    "ampm" : "PM",
                    "day" : 17,
                    "epoch" : "1358478000",
                    "hour" : 21,
                    "isdst" : "0",
                    "min" : "00",
                    "month" : 1,
                    "monthname" : "January",
                    "pretty" : "9:00 PM CST on January 17, 2013",
                    "sec" : 0,
                    "tz_long" : "America/Chicago",
                    "tz_short" : "CST",
                    "weekday" : "Thursday",
                    "weekday_short" : "Thu",
                    "yday" : 16,
                    "year" : 2013
                },
                "high" : {
                    "celsius" : "11",
                    "fahrenheit" : "52"
                },
                "icon" : "clear",
                "icon_url" : "http://icons-ak.wxug.com/i/c/k/clear.gif",
                "low" : {
                    "celsius" : "-2",
                    "fahrenheit" : "28"
                },
                "maxhumidity" : 76,
                "maxwind" : {
                    "degrees" : 340,
                    "dir" : "NNW",
                    "kph" : 18,
                    "mph" : 11
                },
                "minhumidity" : 38,
                "period" : 1,
                "pop" : 10,
                "qpf_allday" : {
                    "in" : 0.0,
                    "mm" : 0.0
                },
                "qpf_day" : {
                    "in" : 0.0,
                    "mm" : 0.0
                },
                "qpf_night" : {
                    "in" : 0.0,
                    "mm" : 0.0
                },
                "skyicon" : "mostlysunny",
                "snow_allday" : {
                    "cm" : 0,
                    "in" : 0
                },
                "snow_day" : {
                    "cm" : 0,
                    "in" : 0
                },
                "snow_night" : {
                    "cm" : 0,
                    "in" : 0
                }
            },
            {
                "avehumidity" : 59,
                "avewind" : {
                    "degrees" : 172,
                    "dir" : "South",
                    "kph" : 6,
                    "mph" : 4
                },
                "conditions" : "Clear",
                "date" : {
                    "ampm" : "PM",
                    "day" : 18,
                    "epoch" : "1358564400",
                    "hour" : 21,
                    "isdst" : "0",
                    "min" : "00",
                    "month" : 1,
                    "monthname" : "January",
                    "pretty" : "9:00 PM CST on January 18, 2013",
                    "sec" : 0,
                    "tz_long" : "America/Chicago",
                    "tz_short" : "CST",
                    "weekday" : "Friday",
                    "weekday_short" : "Fri",
                    "yday" : 17,
                    "year" : 2013
                },
                "high" : {
                    "celsius" : "10",
                    "fahrenheit" : "50"
                },
                "icon" : "clear",
                "icon_url" : "http://icons-ak.wxug.com/i/c/k/clear.gif",
                "low" : {
                    "celsius" : "-1",
                    "fahrenheit" : "30"
                },
                "maxhumidity" : 84,
                "maxwind" : {
                    "degrees" : 170,
                    "dir" : "South",
                    "kph" : 10,
                    "mph" : 6
                },
                "minhumidity" : 40,
                "period" : 2,
                "pop" : 0,
                "qpf_allday" : {
                    "in" : 0.0,
                    "mm" : 0.0
                }, ..................

Now the part I’m only interested in is forecastday. So what i did is the following:

package entity.json;

import java.util.List;

public class Data {
    private List<Forecast> forecastday;

    public List<Forecast> getForecastdays() {
        return forecastday;
    }
}

Forecast class:

package entity.json;

public class Forecast {
    private int avehumidity;
    private Avewind avewind;
    private String conditions;
    private DateWeather date;
    private CelciusHigh high;
    private String icon_url;
    private CelciusLow low;
    // + constructor, getters, setters

Here is my method:

public void createWeatherForecast(){
        String text = "";
        try {
            URL url = new URL(jsonUrl);
            System.out.println(jsonUrl);
            Scanner s = new Scanner(url.openStream());
            while(s.hasNextLine()){
                text += s.nextLine();
            }
            Data weather = new Gson().fromJson(text, Data.class);
            System.out.println(new Gson().toJson(weather));
            System.out.println(weather.getForecastdays().get(0).getAvewind());
        } catch (IOException ex) {
            Logger.getLogger(WeatherController.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Now should I also be focussing on forecast and simpleforecast?

Answer 1

Just because you’re “only interested” in one part of the JSON object doesn’t make Gson magically be able to provide that 😉

You either need to make your POJO to match the JSON object, or write a custom deserializer that discards the portion of the JSON object you’re not interested in and returns an instance of your Data class.