RssParserService.java

/**
 * Copyright 2008 The University of North Carolina at Chapel Hill
 *
 * 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 edu.unc.lib.dl.ui.service;

import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.Namespace;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.List;

import edu.unc.lib.dl.ui.model.response.RssFeedBean;

/**
 * Retrieves and processes RSS feeds
 * 
 * @author bbpennel
 */
public class RssParserService extends XMLRetrievalService {
	private static final Logger LOG = LoggerFactory.getLogger(RssParserService.class);
	private static final Namespace CONTENT = Namespace.getNamespace("content", "http://purl.org/rss/1.0/modules/content/");

	public static RssFeedBean getRssFeed(String url) throws Exception {
		return getRssFeed(url, -1);
	}

	public static RssFeedBean getRssFeed(String url, int maxResults) throws Exception {
		try {
			Document document = getXMLDocument(url);
			return buildRssFeed(document, maxResults);
		} catch (Exception e) {
			// if we get an error trying to build from a non-valid uri,
			// just return an empty LookupTable
			LOG.error("Failed to retrieve RSS feed " + url, e);
		}
		return null;
	}

	private static RssFeedBean buildRssFeed(Document document, int maxResults) throws Exception {
		RssFeedBean rssFeed = new RssFeedBean();
		Element rootElement = null;
		Element channelElement = null;
		String rssFeedVersion = null;

		if (null == document)
			throw new Exception("Empty document");

		rootElement = document.getRootElement();
		if (!"rss".equalsIgnoreCase(rootElement.getName()))
			throw new Exception("Invalid XML");

		rssFeedVersion = rootElement.getAttributeValue("version");
		channelElement = rootElement.getChild("channel");
		if (null == channelElement)
			throw new Exception("Empty feed");

		// Getting the feed contents
		rssFeed = getHeader(channelElement);
		rssFeed.setVersion(rssFeedVersion);
		addFeedItems(channelElement, rssFeed, maxResults);

		return (rssFeed);
	}

	private static RssFeedBean getHeader(org.jdom2.Element channelElement) {
		// Sets the RSS feed header information to the
		// RssFeedBean object
		RssFeedBean rssFeed = new RssFeedBean();
		rssFeed.setTitle(getValueOfChildElement(channelElement, "title"));
		rssFeed.setLink(getValueOfChildElement(channelElement, "link"));
		rssFeed.setDescription(getValueOfChildElement(channelElement, "description"));
		return rssFeed;
	}

	// Get the child node value
	private static String getValueOfChildElement(Element parentElement, String tagName, Namespace ns) {
		Element childElement = null;
		String tagValue = null;
		childElement = parentElement.getChild(tagName, ns);
		tagValue = (null != childElement) ? childElement.getValue().trim() : null;
		return (tagValue);
	}
	
	private static String getValueOfChildElement(Element parentElement, String tagName) {
		return getValueOfChildElement(parentElement, tagName, null);
	}

	private static RssFeedBean.RssItem.EnclosureObject getEnclosure(Element parentElement) {
		Element childElement = null;

		childElement = parentElement.getChild("enclosure");
		if (childElement == null)
			return null;
		RssFeedBean.RssItem.EnclosureObject enclosureObject = new RssFeedBean.RssItem.EnclosureObject();
		enclosureObject.setUrl(childElement.getAttribute("url").getValue());
		enclosureObject.setType(childElement.getAttribute("type").getValue());
		enclosureObject.setLength(childElement.getAttribute("length").getValue());
		return enclosureObject;
	}

	@SuppressWarnings("unchecked")
	private static void addFeedItems(Element channelElement, RssFeedBean rssFeed, int maxResults) {
		List<Element> itemElements = null;
		RssFeedBean.RssItem anRssItem = null;

		itemElements = channelElement.getChildren("item");
		if (null != itemElements) {
			if (maxResults == -1) {
				maxResults = itemElements.size();
			}
			for (int i = 0; i < maxResults; i++) {
				Element anItemElement = itemElements.get(i);
				anRssItem = new RssFeedBean.RssItem(); 
				anRssItem.setTitle(getValueOfChildElement(anItemElement, "title"));
				anRssItem.setLink(getValueOfChildElement(anItemElement, "link"));
				anRssItem.setDescription(getValueOfChildElement(anItemElement, "description"));
				anRssItem.setPubDate(getValueOfChildElement(anItemElement, "pubDate"));
				anRssItem.setGuid(getValueOfChildElement(anItemElement, "guid"));
				anRssItem.setEncoded(getValueOfChildElement(anItemElement, "encoded", CONTENT));
				anRssItem.setEnclosure(getEnclosure(anItemElement));
				rssFeed.items.add(anRssItem);
			}
		}
	}
}