Parse JSON and create objects

Question

In my app I've to parse this JSON:

programs.json

{
  "programs": {
    "program": [
      {
        "programNumber": "1",
        "imgURL": "http://www.photovideolife.com/userfiles/Placeholder%2001.jpg",
        "description": "Lorem ipsum dolor sit er elit",
        "episode": [
          {
            "pN": "1",
            "episodeNumber": "1",
            "transmissionName": "Titolo",
            "date": "29 Giu 2013",
            "time": "14:30",
            "channel": "Real Time",
            "channelLogo": "https://lh6.googleusercontent.com/-XSh-9ngYJu4/ThiY-xl2EeI/AAAAAAAABmc/iz04VpL5hOs/s800/realtime.png"
          },
          {
            "pN": "1",
            "episodeNumber": "1",
            "transmissionName": "Titolo",
            "date": "29 Giu 2013",
            "time": "16:30",
            "channel": "DMAX",
            "channelLogo": "http://tv.zam.it/canali/dmax.png"
          },
          {
            "pN": "1",
            "episodeNumber": "2",
            "transmissionName": "Titolo",
            "date": "01 Lug 2013",
            "time": "14:30",
            "channel": "Real Time",
            "channelLogo": "https://lh6.googleusercontent.com/-XSh-9ngYJu4/ThiY-xl2EeI/AAAAAAAABmc/iz04VpL5hOs/s800/realtime.png"
          },
          {
            "pN": "1",
            "episodeNumber": "2",
            "transmissionName": "Titolo",
            "date": "01 Lug 2013",
            "time": "16:30",
            "channel": "DMAX",
            "channelLogo": "http://tv.zam.it/canali/dmax.png"
          }
        ]
      },
      {
        "programNumber": "2",
        "imgURL": "http://mesa.umich.edu/files/mesa/field/image/placeholder2.png",
        "description": "Lorem ipsum dolor sit er elit",
        "Episode": [
          {
            "pN": "2",
            "episodeNumber": "1",
            "transmissionName": "Titolo 1",
            "date": "30 Giu 2013",
            "time": "13:30",
            "channel": "Real Time",
            "channelLogo": "https://lh6.googleusercontent.com/-XSh-9ngYJu4/ThiY-xl2EeI/AAAAAAAABmc/iz04VpL5hOs/s800/realtime.png"
          },
          {
            "pN": "2",
            "episodeNumber": "1",
            "transmissionName": "Titolo 1",
            "date": "30 Giu 2013",
            "time": "18:30",
            "channel": "DMAX",
            "channelLogo": "http://tv.zam.it/canali/dmax.png"
          },
          {
            "pN": "2",
            "episodeNumber": "2",
            "transmissionName": "Titolo 1",
            "date": "01 Lug 2013",
            "time": "13:30",
            "channel": "Real Time",
            "channelLogo": "https://lh6.googleusercontent.com/-XSh-9ngYJu4/ThiY-xl2EeI/AAAAAAAABmc/iz04VpL5hOs/s800/realtime.png"
          },
          {
            "pN": "2",
            "episodeNumber": "2",
            "transmissionName": "Titolo 1",
            "date": "01 Lug 2013",
            "time": "18:30",
            "channel": "DMAX",
            "channelLogo": "http://tv.zam.it/canali/dmax.png"
          }
        ]
      },
      {
        "programNumber": "3",
        "imgURL": "http://wp.contempographicdesign.com/wp_paramount/wp-content/themes/paramount/images/image_placeholder_lrg.jpg",
        "description": "Lorem ipsum dolor sit er elit",
        "Episode": [
          {
            "pN": "3",
            "episodeNumber": "1",
            "transmissionName": "Titolo 2",
            "date": "30 Giu 2013",
            "time": "10:30",
            "channel": "Real Time",
            "channelLogo": "https://lh6.googleusercontent.com/-XSh-9ngYJu4/ThiY-xl2EeI/AAAAAAAABmc/iz04VpL5hOs/s800/realtime.png"
          },
          {
            "pN": "3",
            "episodeNumber": "1",
            "transmissionName": "Titolo 2",
            "date": "30 Giu 2013",
            "time": "17:30",
            "channel": "DMAX",
            "channelLogo": "http://tv.zam.it/canali/dmax.png"
          },
          {
            "pN": "3",
            "episodeNumber": "2",
            "transmissionName": "Titolo 2",
            "date": "01 Lug 2013",
            "time": "10:30",
            "channel": "Real Time",
            "channelLogo": "https://lh6.googleusercontent.com/-XSh-9ngYJu4/ThiY-xl2EeI/AAAAAAAABmc/iz04VpL5hOs/s800/realtime.png"
          },
          {
            "pN": "3",
            "episodeNumber": "2",
            "transmissionName": "Titolo 2",
            "date": "01 Lug 2013",
            "time": "17:30",
            "channel": "DMAX",
            "channelLogo": "http://tv.zam.it/canali/dmax.png"
          }
        ]
      }
    ]
  }
}

I wanted to create some objects to store data from this JSON file so I used the Gson library to make this parsing very easy. I'm having trouble to create objects by using this library, I created 4 objects:

EpisodeData in which I store this informations (pN, episodeNumber, date, time, channel and channelLogo)
Episode it's an array of EpisodeData
Program it's an array of Episode
Programs in which I store the array Program

Here's the code of the objects:

EpisodeData.java

public class EpisodeData implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    public String pN, episodeNumber, transmissionName, date, time, channel, channelLogo;
}

Episode.java

public class Episode implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    public EpisodeData[] episodeData;
}

Program.java

public class Program implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    public Episode[] episode; 
}

Programs.java

public class Programs implements Serializable {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    public Program program;

}

So I made the connection (with AsyncHttpClient) to download the JSON file from a server and I started to parse it, but I'm having trouble. I post here the code snippet:

public void onSuccess(String json) {
   super.onSuccess(json);
   Gson decoder = new Gson();
   Programs programs = decoder.fromJson(json, Programs.class);
   Log.d("PROGRAMS", "" + programs.program);
}

Why I can't access to Episode and EpisodeData? Why when I try to log programs.program it returns null?

I hope you can help me to find a solution for this issue Thank you

You are not creating problem classes for fetching data. check this demo — Lalit Poptani
– Lalit Poptani, Commented Aug 6, 2013 at 7:58
The code you say it doesn't work... I tried on my galaxy S2 and it shows me a white activity — lucgian84
– lucgian84, Commented Aug 6, 2013 at 8:07
Episode should have as much attributes as you want to parse, named exactly as they come in the json. As they starts with a "-" you can't neither rename the class' attributtes nor parse them as they have different names than Gson is expecting. Try to replace -pN with pN, -episodeNumber with episodeNumber and so on before you call decoder.fromJson like this: json.replaceAll("-pN", "pN"); etc. — Adrián Rodríguez
– Adrián Rodríguez, Commented Aug 6, 2013 at 8:08
@AdriánRodríguez: I will try it in a second and I will tell you if it works or not just a moment — lucgian84
– lucgian84, Commented Aug 6, 2013 at 8:11
@AdriánRodríguez: same problem: I changed the JSON entry by deleting the the -. I saw that in JSON I've Programs and Program and in my java class I've programs and program so I edited my JSON so: Programs -> programs and Program -> program, but still the same, when I write this Log.d("PROGRAMS", "" + programs.program); it shows me null... Why? I've update my JSON in my question — lucgian84
– lucgian84, Commented Aug 6, 2013 at 8:21

Adrián Rodríguez · Accepted Answer · 2013-08-06 09:33:40Z

The problem is in the base object. It should not be Programs but another object that has a Programs attribute. Apart from that, the Programs object has an array of Program as attribute, not a single instance.

Base object:

public class JsonRootObject {

    public Programs programs;

}

Programs object:

public class Programs implements Serializable {

    private static final long serialVersionUID = 1L;
    public Program []program;

}

Program object:

public class Program implements Serializable {

    private static final long serialVersionUID = 1L;
    public Episode[] episode; 
}

Episode object:

public class Episode implements Serializable {

    private static final long serialVersionUID = 1L;
    public String pN, episodeNumber, transmissionName, date, time, channel, channelLogo;
    @Override
    public String toString() {
        return "Episode [pN=" + pN + ", episodeNumber=" + episodeNumber
                + ", transmissionName=" + transmissionName + ", date="
                + date + ", time=" + time + ", channel=" + channel
                + ", channelLogo=" + channelLogo + "]";
    }
}

EpisodeData is not needed, as Episode is the last level.

And finally you can parse it with:

Gson decoder = new Gson();
JsonRootObject programs = decoder.fromJson(json, JsonRootObject.class);

I added a toString method to Episode class to test the parser, and this is the result:

System.out.println(programs.programs.program[0].episode[0]);

08-06 05:31:58.236: I/System.out(1249): Episode [pN=1, episodeNumber=1, transmissionName=Titolo, date=29 Giu 2013, time=14:30, channel=Real Time, channelLogo=https://lh6.googleusercontent.com/-XSh-9ngYJu4/ThiY-xl2EeI/AAAAAAAABmc/iz04VpL5hOs/s800/realtime.png]

Hope that helps :)

JaredLuo · Accepted Answer · 2013-08-06 08:35:36Z

0

I think You should add @@SerializedName("-pN") above declaration of field pN, and do this to other fields too.

edited Aug 6, 2013 at 8:35

answered Aug 6, 2013 at 8:22

JaredLuo

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