Question

I am accessing web pages through java as follows:

URLConnection con = url.openConnection();

But in some cases, a url redirects to another url. So I want to know the url to which the previous url redirected.

Below are the header fields that I got as a response:

null-->[HTTP/1.1 200 OK]
Cache-control-->[public,max-age=3600]
last-modified-->[Sat, 17 Apr 2010 13:45:35 GMT]
Transfer-Encoding-->[chunked]
Date-->[Sat, 17 Apr 2010 13:45:35 GMT]
Vary-->[Accept-Encoding]
Expires-->[Sat, 17 Apr 2010 14:45:35 GMT]
Set-Cookie-->[cl_def_hp=copenhagen; domain=.craigslist.org; path=/; expires=Sun, 17     Apr 2011 13:45:35 GMT, cl_def_lang=en; domain=.craigslist.org; path=/; expires=Sun, 17 Apr 2011 13:45:35 GMT]
Connection-->[close]
Content-Type-->[text/html; charset=iso-8859-1;]
Server-->[Apache]

So at present, I am constructing the redirected url from the value of the Set-Cookie header field. In the above case, the redirected url is copenhagen.craigslist.org

Is there any standard way through which I can determine which url the particular url is going to redirect.

I know that when a url redirects to other url, the server sends an intermediate response containing a Location header field that tells the redirected url but I am not receiving that intermediate response through the url.openConnection(); method.

Answer 1

You need to cast the URLConnection to HttpURLConnection and instruct it to not follow the redirects by setting HttpURLConnection#setInstanceFollowRedirects() to false. You can also set it globally by HttpURLConnection#setFollowRedirects().

You only need to handle redirects yourself then. Check the response code by HttpURLConnection#getResponseCode(), grab the Location header by URLConnection#getHeaderField() and then fire a new HTTP request on it.