Get the URL of the HTTP redirect destination in Java

Overview

--Get the URL of the HTTP redirect destination in Java

Java 11 version

Save the following contents with the file name GetRedirect.java.

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.util.Optional;

public class GetRedirect {

  public static void main(String[] args) throws Exception {

    //Get command line arguments
    String srcUrl = args[0];

    //Get the redirect URL
    Optional<String> redirectUrl = getRedirectUrl(srcUrl);

    //Output redirect URL
    redirectUrl.ifPresent(url -> System.out.println(url));
  }

  //Get the redirect URL
  public static Optional<String> getRedirectUrl(String srcUrl) throws URISyntaxException, IOException, InterruptedException {

    //Build HTTP request information
    HttpRequest req = HttpRequest.newBuilder(new URI(srcUrl)).GET().build();

    //HTTP request
    //Note that HttpClient does not raise an exception even with 4xx or 5xx
    HttpClient client = HttpClient.newBuilder()
      .version(HttpClient.Version.HTTP_1_1)
      .followRedirects(HttpClient.Redirect.NEVER) //Setting not to redirect automatically
      .build();
    HttpResponse<String> res = client.send(req, HttpResponse.BodyHandlers.ofString());

    //Get Location header from HTTP response
    return res.headers().firstValue("location");
  }
}

Execution example by Java 11 (AdoprOpenJDK 11.0.8) + macOS Catalina.

$ java GetRedirect.java https://bit.ly/3kmTOkc
https://t.co/yITSBp4ino

$ java GetRedirect.java https://t.co/yITSBp4ino
https://qiita.com/niwasawa

$ java GetRedirect.java https://qiita.com/niwasawa

Java 8 version

Save the following contents with the file name GetRedirect.java.

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;

public class GetRedirect {

  public static void main(String[] args) throws IOException {

    //Get command line arguments
    String srcUrl = args[0];

    //Get the redirect URL
    String redirectUrl = getRedirectUrl(srcUrl);

    //Output redirect URL
    if (redirectUrl != null) {
      System.out.println(redirectUrl);
    }
  }

  //Get the redirect URL
  public static String getRedirectUrl(String srcUrl) throws IOException {
    //Note that 4xx and 5xx do not raise an exception
    HttpURLConnection con = (HttpURLConnection) new URL(srcUrl).openConnection();
    con.setRequestMethod("GET");
    con.setInstanceFollowRedirects(false); //Setting not to redirect automatically
    con.connect();
    //Get Location header from HTTP response
    String location = con.getHeaderField("location");
    con.disconnect();
    return location;
  }
}

Execution example by Java 8 (AdoprOpenJDK 1.8.0_265) + macOS Catalina.

compile.

$ javac GetRedirect.java

Run.

$ java GetRedirect https://bit.ly/3kmTOkc
https://t.co/yITSBp4ino

$ java GetRedirect https://t.co/yITSBp4ino
https://qiita.com/niwasawa

$ java GetRedirect https://qiita.com/niwasawa

Reference material

• java.net.http (Java SE 11 & JDK 11 )
• HttpURLConnection (Java Platform SE 8 ) -HTTP Redirection -HTTP \ | MDN
• Location - HTTP | MDN