Parsing JSON from URL

Question

Is there any simplest way to parse JSON from a URL? I used Gson I can't find any helpful examples.

Answer 1

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(); } 

Answer 2

GSON has a builder that takes a Reader object: fromJson(Reader json, Class classOfT).

This means you can create a Reader from a URL and then pass it to Gson to consume the stream and do the deserialisation.

Only three lines of relevant code.

import java.io.InputStreamReader; import java.net.URL; import java.util.Map;  import com.google.gson.Gson;  public class GsonFetchNetworkJson {      public static void main(String[] ignored) throws Exception {          URL url = new URL("https://httpbin.org/get?color=red&shape=oval");         InputStreamReader reader = new InputStreamReader(url.openStream());         MyDto dto = new Gson().fromJson(reader, MyDto.class);          // using the deserialized object         System.out.println(dto.headers);         System.out.println(dto.args);         System.out.println(dto.origin);         System.out.println(dto.url);     }      private class MyDto {         Map<String, String> headers;         Map<String, String> args;         String origin;         String url;     } } 

^{If you happen to get a 403 error code with an endpoint which otherwise works fine (e.g. with curl or other clients) then a possible cause could be that the endpoint expects a User-Agent header and by default Java URLConnection is not setting it. An easy fix is to add at the top of the file e.g. System.setProperty("http.agent", "Netscape 1.0");.}