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();}

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");.}

You could use org.apache.commons.io.IOUtils for downloading and org.json.JSONTokener for parsing:

JSONObject jo = (JSONObject) new JSONTokener(IOUtils.toString(new URL("http://gdata.youtube.com/feeds/api/videos/SIFL9qfmu5U?alt=json"))).nextValue();System.out.println(jo.getString("version"));