Quickest way to get content type

Question

I need to chech for the content type (if it's image, audio or video) of an url which has been inserted by the user. I have a code like this:

URL url = new URL(urlname);
URLConnection connection = url.openConnection();
connection.connect();
String contentType = connection.getContentType();

I'm getting the content type, but the problem is that it seems that it is necessary to download the whole file to check it's content type. So it last too much time when the file is quite big. I need to use it in a Google App Engine aplication so the requests are limited to 30 seconds.

Is there any other way to get the content type of a url without downloading the file (so it could be done quicker)?

Answer 1

Be aware of redirects, I faced same problem with my remote content check.
Here is my fix:

/**
 * Http HEAD Method to get URL content type
 *
 * @param urlString
 * @return content type
 * @throws IOException
 */
public static String getContentType(String urlString) throws IOException{
    URL url = new URL(urlString);
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("HEAD");
    if (isRedirect(connection.getResponseCode())) {
        String newUrl = connection.getHeaderField("Location"); // get redirect url from "location" header field
        logger.warn("Original request URL: '{}' redirected to: '{}'", urlString, newUrl);
        return getContentType(newUrl);
    }
    String contentType = connection.getContentType();
    return contentType;
}

/**
 * Check status code for redirects
 * 
 * @param statusCode
 * @return true if matched redirect group
 */
protected static boolean isRedirect(int statusCode) {
    if (statusCode != HttpURLConnection.HTTP_OK) {
        if (statusCode == HttpURLConnection.HTTP_MOVED_TEMP
            || statusCode == HttpURLConnection.HTTP_MOVED_PERM
                || statusCode == HttpURLConnection.HTTP_SEE_OTHER) {
            return true;
        }
    }
    return false;
}

You could also put some counter for maxRedirectCount to avoid infinite redirects loop - but this is not covered here. This is just a inspiration.

Answer 2

Thanks to DaveHowes answer and googling around about how to get HEAD I got it in this way:

URL url = new URL(urlname);
HttpURLConnection connection = (HttpURLConnection)  url.openConnection();
connection.setRequestMethod("HEAD");
connection.connect();
String contentType = connection.getContentType();

Answer 3

If the "other" end supports it, could you use the HEAD HTTP method?