import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Optional;
import java.util.zip.GZIPInputStream;

import org.apache.abdera.Abdera;
import org.apache.abdera.model.Document;
import org.apache.abdera.model.Feed;
import org.apache.abdera.parser.Parser;

/**
 * Utility class to parse Atom feed.
 * 
 * Usage :
 * 

 * 
Instantiate FeedUtil with atom document url. Call the getFeed method
 * 
to get the feed document associated with url.
 * 
 * 
 * @author Hari Krishna Gurram
 *
 */
public class FeedUtil {
private String url;
private InputStream in = null;
private Feed feed = null;
 HttpURLConnection conn = null;

public FeedUtil(String url) {
this.url = url;
}

/**
  * 
  * @param url
  * @return Optional.empty if url is null (or) unable to parse the url, else
  *         return the Document object.
  */
private OptionalDocumentFeed>> getDocument() {
if (url == null) {
return Optional.empty();
}

try {
   URL urlTemp = new URL(url);

   conn = (HttpURLConnection) urlTemp.openConnection();
   conn.setRequestProperty("Accept-Encoding", "gzip");
   conn.connect();

   String contentEncoding = conn.getContentEncoding();
boolean isGzip = contentEncoding != null && contentEncoding.contains("gzip");

   in = !isGzip ? conn.getInputStream() : new GZIPInputStream(conn.getInputStream());
   Abdera abdera = Abdera.getInstance();
   Parser parser = abdera.getParser();
   DocumentFeed> document = parser.parse(in, url.toString());
return Optional.of(document);

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

return Optional.empty();
}

/**
  * 
  * @return the Feed object associated with given {@link url}. In any case if
  *         the feed creation is failed, then it return Optional.empty().
  */

public synchronized OptionalFeed> getFeed() {
if (feed != null) {
return Optional.of(feed);
}

  OptionalDocumentFeed>> documentOpt = getDocument();

if (!documentOpt.isPresent()) {
return Optional.empty();
}

  DocumentFeed> document = documentOpt.get();

  feed = document.getRoot();
return Optional.of(feed);
}

public void closeStreamAndConnection() {
if (in != null) {
try {
    in.close();
    System.out.println("Input Stream is closed");
} catch (IOException e1) {
    e1.printStackTrace();
}
}

if (conn != null) {
   conn.disconnect();
   System.out.println("Input stream is disconnected");
}
}

/**
  * This is just a safety check, if user forget to close the stram, it will
  * be closed once object is out of scope.
  */
@Override
public void finalize() {
  closeStreamAndConnection();
}
}