Simplest Way to Read Json from a Url in Java

Parsing JSON from URL

1. First you need to download the URL (as text):

   private static String readUrl(String urlString) throws Exception {
       BufferedReader reader = null;
       try {
           URL url = new URL(urlString);
           reader = new BufferedReader(new InputStreamReader(url.openStream()));
           StringBuffer buffer = new StringBuffer();
           int read;
           char[] chars = new char[1024];
           while ((read = reader.read(chars)) != -1)
               buffer.append(chars, 0, read); 
   
           return buffer.toString();
       } finally {
           if (reader != null)
               reader.close();
       }
   }
   

2. Then you need to parse it (and here you have some options).

   • GSON (full example):

     static class Item {
         String title;
         String link;
         String description;
     }
     
     static class Page {
         String title;
         String link;
         String description;
         String language;
         List<Item> items;
     }
     
     public static void main(String[] args) throws Exception {
     
         String json = readUrl("http://www.javascriptkit.com/"
                               + "dhtmltutors/javascriptkit.json");
     
         Gson gson = new Gson();        
         Page page = gson.fromJson(json, Page.class);
     
         System.out.println(page.title);
         for (Item item : page.items)
             System.out.println("    " + item.title);
     }
     

     Outputs:

     javascriptkit.com
         Document Text Resizer
         JavaScript Reference- Keyboard/ Mouse Buttons Events
         Dynamically loading an external JavaScript or CSS file
     

   • Try the java API from json.org:

     try {
         JSONObject json = new JSONObject(readUrl("..."));
     
         String title = (String) json.get("title");
         ...
     
     } catch (JSONException e) {
         e.printStackTrace();
     }
     

Easy way to Get JSON From URL

You can use third party libraries like volley, retrofit....
for example with volley you should make a JsonArrayRequest to the server and parse it.

Farsi resource

English resource

and this is a basic request:

JsonArrayRequest jarr = new JsonArrayRequest(Request.Method.GET, URL, null, new Response.Listener<JSONArray>() {
        @Override
        public void onResponse(JSONArray response) {

            try{

                for(int i=0;i<response.length();i++){
                    JSONObject job = response.getJSONObject(i);
                    String name = job.getString("name");

                }

            } catch (Exception e){


            }
        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {


        }
    });

    requestQueue.add(jarr);

how i get JSON as string from url (java)

You can use Spring's RestTemplate to get the response as String, e.g.:

RestTemplate restTemplate = new RestTemplate();
String response = restTemplate.getForObject("https://www.instagram.com/ihanan95/?__a=1", String.class);
System.out.println(response);

If you are not allowed to use third party libaries then you can do the same with URLConnection, e.g.:

URLConnection connection = new URL("https://www.instagram.com/ihanan95/?__a=1").openConnection();
try(Scanner scanner = new Scanner(connection.getInputStream());){
    String response = scanner.useDelimiter("\\A").next();
    System.out.println(response);
}

How to parse JSON data form URL?

You need to deserialize a list of ProDesc objects because your main JSON is an array.

This is how I deserialize something similar with Jackson 2.1.4:

List<ProDesc> proDescList = objMapper.readValue(jsondata, objMapper.getTypeFactory().constructParametricType(List.class, ProDesc.class));

EDIT: If your ProDesc class contains only the id member, you need to tell Jackson to ignore the other members with an annotation like so:

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown=true)
public class ProDesc {

    private int id;

    public ProDesc(){}

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }
}

---

Related Topics