Question

i’m trying to retrieve text from wikipedia to use on an Android app. I’m using Java.
The first thing I want to do is to retrieve the sections from an specific article, show them to the user and, when the user clicks on one section, get the section text with another http request.

So, the two requests are these:

http://en.wikipedia.org/w/api.php?format=json&action=parse&page=Valencia_Cathedral&prop=sections

and then this one:

http://en.wikipedia.org/w/api.php?format=json&action=parse&page=Valencia_Cathedral&prop=text&section=1

My question is: What kind of java objects should I create to store the information and then convert it to these classes using .fromJSON()?

Thanks to @NathanZ, I created these two classes:

public class WikiResponseSections {
    String title;
    List<Section> sections;
}

public class Section {
        int toclevel;
        String level;
        String line;
        String number;
        String index;
        String fromtitle;
        int byteoffset;
        String anchor;
}

But, when I convert the HTTP response to these objets by Gson, and try to read the value of the field ‘title’ there’s an error that triggers: JavaNullPointerException.
Here’s my code for the conversion:

InputStream stream = null;
try {
    stream = entity.getContent();
} catch (IllegalStateException e) {
    Log.e("Stream","ERROR illegalstateexception");
} catch (IOException e) {
    Log.e("Stream","ERROR exception");
}
reader = new BufferedReader(new InputStreamReader(stream));
GsonBuilder bldr = new GsonBuilder();
Gson gson = bldr.create();
WikiResponse = gson.fromJson(reader, WikiResponseSections.class);
if (WikiResponse != null){
    Log.i("WikiResponse",WikiResponse.getTitle()); //The error triggers HERE
    publishProgress();
}
else
    Log.i("WikiResponse","NULL");
}

Thanks for your help again

Answer 1

You can use the Google’s Gson library.
It works like this:

InputStream source = ...; // your code to get the Json from a url
Gson gson = new Gson();
Reader reader = new InputStreamReader(source);
MyResponse response = gson.fromJson(reader, MyResponse.class);

Where MyResponse is your object. When you create MyResponse, give your fields the same name and type as the Json’s fields

MyResponse class can be as follows:

public class MyResponse{
    String title;
    ArrayList<sections>;
}

public class sections{
    int toclevel;
    String level;
    String line;
    String number;
    String fromtitle;
    long byteoffset;
    String anchor;
}



public class WikiResponseParse{
    Parse parse;
    public class Parse{
        String title, text;
    }
}

If you can’t use the json fields name because it’s not Java compliant:

Add the following import:

import com.google.gson.annotations.SerializedName;

and in your class:

@SerializedName("*")
public String star;