guess image content type from URL

GuessContentTypeTest.java

public class GuessContentTypeTest extends TestCase {

    @Test
    public void testGuessFileTypeFromUrl() throws Exception {
        String[] urls = {
                // your image urls here
        };
        for(String s : urls) {
            int pushbackLimit = 100;
            URL url = new URL(s);
            URLConnection conn = url.openConnection();
            InputStream urlStream = conn.getInputStream();
            PushbackInputStream pushbackInputStream = new PushbackInputStream(urlStream, pushbackLimit);
            byte[] firstBytes = new byte[pushbackLimit];
            // download the first initial bytes into a byte array, which we will later pass to
            // URLConnection.guessContentTypeFromStream
            pushbackInputStream.read(firstBytes);
            // push the bytes back onto the PushbackInputStream so that the stream can be read
            // by ImageIO reader in its entirety
            pushbackInputStream.unread(firstBytes);

            String imageType = null;
            // Pass the initial bytes to URLConnection.guessContentTypeFromStream in the form of a
            // ByteArrayInputStream, which is mark supported.
            ByteArrayInputStream bais = new ByteArrayInputStream(firstBytes);
            String mimeType = URLConnection.guessContentTypeFromStream(bais);
            if(mimeType == null) {
                System.out.println("Cannot guess content type will use connection content-type header");
                mimeType = conn.getContentType();
            }
            if (mimeType == null) {
                System.out.println("Cannot guess and no content-type header");
            }
            else if (mimeType.startsWith("image/")) {
                imageType = mimeType.substring("image/".length());
                System.out.println(imageType);
            }
            else {
                System.out.println("Not Image");
            }
        }
    }
}