Can't get expanded url from shortened url in java

Question

I have the following code which expands the shortened url.

import java.io.IOException;

import java.net.HttpURLConnection;
import java.net.Proxy;
import java.net.URL;
public class ExpandUrl {

    public static void main(String[] args) throws IOException {
        String shortenedUrl = "2q3GMg0"; //read note at the bottom. 
        String expandedURL = ExpandUrl.expand(shortenedUrl);
        System.out.println("expanded url is :  " + expandedURL); 
    }

    public static String expand(String shortenedUrl) throws IOException {
        URL url = new URL(shortenedUrl);    
        // open connection
        HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection(Proxy.NO_PROXY); 

      int status = 0;
      try {
          status = httpURLConnection.getResponseCode();
      } catch (IOException e) {
          e.printStackTrace();
      }

      System.out.println("status is " + status);

        // stop following browser redirect
        httpURLConnection.setInstanceFollowRedirects(false);

        // extract location header containing the actual destination URL
        String expandedURL = httpURLConnection.getHeaderField("Location");
        httpURLConnection.disconnect();

        return expandedURL;
    }
}

The code expands some of the urls but returns null for some other urls. e.g: it expands 2q3GMg0 but returns null when I use 9mglq8 although the status code is 200 for this. I have tested both url. Both are valid and has expanded form.

Note: Stackoverflow didn't allow me to put shortened link in body so I have just mentioned the hashcode.

Edit: Links for which I am getting null doesn't have a Location header field. In such case how do I retrieve the original expanded link?

status is 200
Key: null  value: [HTTP/1.1 200 OK]
Key: X-Cache  value: [Hit from cloudfront]
Key: Server  value: [Apache]
Key: Connection  value: [keep-alive]
Key: Last-Modified  value: [Sat, 12 May 2018 12:06:48 GMT]
Key: Date  value: [Sat, 12 May 2018 12:11:30 GMT]
Key: Via  value: [1.1 587a74dd892ff33ecf276aa569c8b68a.cloudfront.net (CloudFront)]
Key: X-Frame-Options  value: [SAMEORIGIN]
Key: Accept-Ranges  value: [bytes]
Key: Cache-Control  value: [max-age=120, s-maxage=120, public]
Key: X-Amz-Cf-Id  value: [-p1_VjHmvcGCI1PbQelSHpUectu_5NfCFUnPu_NUHCJ9_2lS2rTmlA==]
Key: Vary  value: [Accept-Encoding]
Key: X-XSS-Protection  value: [1]
Key: Content-Length  value: [186539]
Key: Age  value: [108]
Key: Content-Type  value: [text/html]

Any kind of help will be greatly appreciated.

Answer 1

If the status code is 200 there is no redirection and there will be no Location field in the header and hence null is returned when you try to access the value of Location key. you can get the expanded URL using httpURLConnection.getURL().

If the status code is 301 or 302 there is a redirection and there will be a Location field in the header. You can get the redirected URL as:

String expandedURL = httpURLConnection.getHeaderField("Location");

like you have done.

hope this helps.