301-redirect

The HttpURLConnection‘s follow redirect is just an indicator, in fact it won’t help you to do the “real” http redirection, you still need to handle it manually.


URL obj = new URL(url);
HttpURLConnection conn = (HttpURLConnection) obj.openConnection();
conn.setInstanceFollowRedirects(true);  //you still need to handle redirect manully.
HttpURLConnection.setFollowRedirects(true);

1. Java Http Redirect Example

If a server is redirected from the original URL to another URL, the response code should be 301: Moved Permanently or 302: Temporary Redirect. And you can get the new redirected url by reading the “Location” header of the HTTP response header.

For example, access to the normal HTTP twitter website – http://www.twitter.com , it will auto redirect to the HTTPS twitter website – https://www.twitter.com.

HttpRedirectExample – Full Java follow redirect example, see comments for self-explanatory.

package com.mkyong.http;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpRedirectExample {

  public static void main(String[] args) {

    try {

	String url = "http://www.twitter.com";

	URL obj = new URL(url);
	HttpURLConnection conn = (HttpURLConnection) obj.openConnection();
	conn.setReadTimeout(5000);
	conn.addRequestProperty("Accept-Language", "en-US,en;q=0.8");
	conn.addRequestProperty("User-Agent", "Mozilla");
	conn.addRequestProperty("Referer", "google.com");

	System.out.println("Request URL ... " + url);

	boolean redirect = false;

	// normally, 3xx is redirect
	int status = conn.getResponseCode();
	if (status != HttpURLConnection.HTTP_OK) {
		if (status == HttpURLConnection.HTTP_MOVED_TEMP
			|| status == HttpURLConnection.HTTP_MOVED_PERM
				|| status == HttpURLConnection.HTTP_SEE_OTHER)
		redirect = true;
	}

	System.out.println("Response Code ... " + status);

	if (redirect) {

		// get redirect url from "location" header field
		String newUrl = conn.getHeaderField("Location");

		// get the cookie if need, for login
		String cookies = conn.getHeaderField("Set-Cookie");

		// open the new connnection again
		conn = (HttpURLConnection) new URL(newUrl).openConnection();
		conn.setRequestProperty("Cookie", cookies);
		conn.addRequestProperty("Accept-Language", "en-US,en;q=0.8");
		conn.addRequestProperty("User-Agent", "Mozilla");
		conn.addRequestProperty("Referer", "google.com");
								
		System.out.println("Redirect to URL : " + newUrl);

	}

	BufferedReader in = new BufferedReader(
                              new InputStreamReader(conn.getInputStream()));
	String inputLine;
	StringBuffer html = new StringBuffer();

	while ((inputLine = in.readLine()) != null) {
		html.append(inputLine);
	}
	in.close();

	System.out.println("URL Content... \n" + html.toString());
	System.out.println("Done");

    } catch (Exception e) {
	e.printStackTrace();
    }

  }

}

Output


Request URL ... http://www.twitter.com
Response Code ... 301
Redirect to URL : https://twitter.com/
URL Content... 
<!DOCTYPE html><!--[if IE 8]><html class= // twitter.com url content...

Do share if you have better way to handle the HTTP redirection :)

References

  1. HttpURLConnection JavaDoc
  2. HttpURLConnection Android JavaDoc, more examples
  3. Wiki : List of HTTP header fields