Parsing JSON from URL
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 aUser-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");
.
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(); } }
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(); }