如何从Android中的URL读取JSON数据

Question

I am having some issues with the following code. I am trying to read from the following Reddit URL

https://www.reddit.com/r/earthporn/.json?after=

Here is the code that is not correctly being executed.

public static String readContents(String url){
        try{
        InputStream input= new URL(url).openStream();
        Reader reader = new InputStreamReader(input);
        BufferedReader in = new BufferedReader(reader);
        String line, str;
        str = "";
        while ((line=in.readLine()) != null) {
            str += line;
            System.out.println(line);
        }
        return str;
        }catch(IOException e){
            Log.d("READ FAILED", e.toString());
            return null;
        }
    }
}

And here is where I call it from

List<Post> fetchPosts(){
    String raw=RemoteData.readContents(url);
    List<Post> list=new ArrayList<Post>();
    try{
        JSONObject data=new JSONObject(raw).getJSONObject("data");
        JSONArray children=data.getJSONArray("children");

        //Using this property we can fetch the next set of
        //posts from the same subreddit
        after=data.getString("after");

        for(int i=0;i<children.length();i++){
            JSONObject cur=children.getJSONObject(i)
                    .getJSONObject("data");
            Post p=new Post();
            p.title=cur.optString("title");
            p.url=cur.optString("url");
            p.numComments=cur.optInt("num_comments");
            p.points=cur.optInt("score");
            p.author=cur.optString("author");
            p.subreddit=cur.optString("subreddit");
            p.permalink=cur.optString("permalink");
            p.domain=cur.optString("domain");
            p.id=cur.optString("id");
            p.thumbnail=cur.optString("thumbnail");
            if(p.title!=null)
                list.add(p);
        }
    }catch(Exception e){
        Log.e("fetchPosts()",e.toString());
    }
    return list;
}

When debugging I get the following results: Raw is left empty.

Does anyone have any clue as to why this it is not reading anything? I hope I included enough code for it to make sense. If anymore is needed, please let me know.

Answer 1

Hello to get response you must open an HttpsURLConnection the problem that you have is you getting a null response from the URL so you must here is the code that works for me :

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import java.net.MalformedURLException;
import java.net.URL;


import javax.net.ssl.HttpsURLConnection;


public class main {
    public static String getJSON(String url) {
        HttpsURLConnection con = null;
        try {
            URL u = new URL(url);
            con = (HttpsURLConnection) u.openConnection();

            con.connect();


                BufferedReader br = new BufferedReader(new InputStreamReader(con.getInputStream()));
                StringBuilder sb = new StringBuilder();
                String line;
                while ((line = br.readLine()) != null) {
                    sb.append(line + "\n");
                }
                br.close();
                return sb.toString();


        } catch (MalformedURLException ex) {
            ex.printStackTrace();
        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            if (con != null) {
                try {
                    con.disconnect();
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }
        return null;
    }

    public static void main(String[] args) {

        String url = "https://www.reddit.com/r/earthporn/.json?after=";
        System.out.println(getJSON(url));

    }

}