FeedDownloadTask.java

/*
 * Copyright 2015 Petr Bouda
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.joyrest.examples.combiner.manager;

import java.net.URL;
import java.util.Collection;
import java.util.Date;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.stream.Collectors;

import org.joyrest.examples.combiner.model.CombinedFeed;
import org.joyrest.examples.combiner.model.CombinedFeed.CombinedFeedBuilder;
import org.joyrest.examples.combiner.model.FeedEntry;
import org.joyrest.examples.combiner.store.InMemoryDataStore;

import com.sun.syndication.feed.synd.SyndEntry;

/**
 * An instance of this class implements the {@link Runnable#run() run method} with functionality of downloading all entries
 * from feed which
 * are available. These entries are added into the combined feed and stored in the database again (storing means rewrite
 * previous combined
 * feed by a new version with added entries).
 *
 * @author Petr Bouda
 **/
public class FeedDownloadTask implements Runnable {

    private static Logger LOG = Logger.getLogger(FeedDownloadTask.class.getName());

    private final FeedEntryMapper entryMapper = new FeedEntryMapper();

    private final Function<URL, List<SyndEntry>> feedDownloader;
    private final InMemoryDataStore datastore;
    private final String combinedFeedID;

    FeedDownloadTask(Function<URL, List<SyndEntry>> feedDownloader, InMemoryDataStore datastore, String feedId) {
        this.combinedFeedID = feedId;
        this.datastore = datastore;
        this.feedDownloader = feedDownloader;
    }

    @Override
    public void run() {
        CombinedFeed fetchedCombinedFeed = datastore.get(combinedFeedID, CombinedFeed.class);
        if (fetchedCombinedFeed == null) {
            LOG.warning("There is no CombinedFeed for the ID: " + combinedFeedID);
            return;
        }

        List<FeedEntry> entries = fetchedCombinedFeed.getUrls().parallelStream()
            .map(feedDownloader)
            .flatMap(Collection::parallelStream)
            .map(entryMapper)
            .filter(Objects::nonNull)
            .sorted((e1, e2) -> e2.getPublishDate().compareTo(e1.getPublishDate()))
            .collect(Collectors.toList());

        CombinedFeed combinedFeed = CombinedFeedBuilder.of(fetchedCombinedFeed).feedEntries(entries).build();

        datastore.put(combinedFeedID, combinedFeed);

        LOG.log(Level.FINEST, "New entries for the CombinedFeed were downloaded [combined-feed={0}, entries-count={1}]",
            new Object[] {combinedFeed.getId(), entries.size()});
    }

    /**
     * The exception which is used for transform {@link SyndEntry synd entry} to this application-friendly version {@link
     * FeedEntry feed
     * entry}.
     * <p>
     * The class implements {@link Function function interface} for a purpose to use it in the {@link Stream stream}.
     * </p>
     *
     * @author Petr Bouda
     **/
    private static class FeedEntryMapper implements Function<SyndEntry, FeedEntry> {

        @Override
        public FeedEntry apply(SyndEntry entry) {
            if (entry.getDescription() == null) {
                return null;
            }

            String title = entry.getTitle();
            String link = entry.getLink();
            String description = entry.getDescription().getValue();
            Date publishedDate = entry.getPublishedDate();
            return new FeedEntry(title, link, description, publishedDate);
        }
    }
}