BundleResolver.java

/*
 * Copyright (c) 2012 Data Harmonisation Panel
 * 
 * All rights reserved. This program and the accompanying materials are made
 * available under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the License,
 * or (at your option) any later version.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution. If not, see <http://www.gnu.org/licenses/>.
 * 
 * Contributors:
 *     HUMBOLDT EU Integrated Project #030962
 *     Data Harmonisation Panel <http://www.dhpanel.eu>
 */

package eu.esdihumboldt.util.resource.internal;

import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.URL;
import java.util.Enumeration;

import org.eclipse.core.runtime.IConfigurationElement;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;

import de.fhg.igd.slf4jplus.ALogger;
import de.fhg.igd.slf4jplus.ALoggerFactory;
import eu.esdihumboldt.util.io.InputSupplier;
import eu.esdihumboldt.util.resource.ResourceNotFoundException;
import eu.esdihumboldt.util.resource.ResourceResolver;

/**
 * Resource resolver that attempts to find a resource at the URI path in the
 * bundle that registered the resolver as extension.
 * 
 * @author Simon Templer
 */
public class BundleResolver implements ResourceResolver {

	private final Bundle bundle;

	private final ALogger log = ALoggerFactory.getLogger(BundleResolver.class);

	/**
	 * Create a bundle resolver.
	 * 
	 * @param conf the configuration element
	 */
	public BundleResolver(IConfigurationElement conf) {
		String bundleName = conf.getContributor().getName();

		BundleContext context = ResourceBundle.getBundleContext();
		if (context != null) { // OSGi is available
			Bundle contributor = null;

			for (Bundle bundle : ResourceBundle.getBundleContext().getBundles()) {
				if (bundle.getSymbolicName().equals(bundleName)) {
					contributor = bundle;
					break;
				}
			}

			if (contributor == null) {
				throw new IllegalStateException("Contributing bundle not found: " + bundleName);
			}

			this.bundle = contributor;
		}
		else {
			// no OSGi available
			this.bundle = null;
		}
	}

	/**
	 * @see ResourceResolver#resolve(URI)
	 */
	@Override
	public InputSupplier<? extends InputStream> resolve(URI uri) throws ResourceNotFoundException {
		if (bundle != null) {
			// OSGi
			final URL entry = bundle.getEntry(uri.getPath());
			if (entry == null) {
				throw new ResourceNotFoundException("Resource with path " + uri.getPath()
						+ " not contained in bundle " + bundle.getSymbolicName());
			}

			preventDirectoryMatch(uri, entry);

			return new InputSupplier<InputStream>() {

				@Override
				public InputStream getInput() throws IOException {
					return entry.openStream();
				}
			};
		}
		else {
			// no OSGi
			final ClassLoader loader = getClass().getClassLoader(); // ClassLoader.getSystemClassLoader();
			String pathCandidate = uri.getPath();
			final String path = (pathCandidate != null && pathCandidate.startsWith("/"))
					? (pathCandidate.substring(1)) : (pathCandidate);
			Enumeration<URL> resources;
			try {
				resources = loader.getResources(path);
			} catch (IOException e) {
				log.error("Error accessing classpath resource", e);
				throw new ResourceNotFoundException(e);
			}

			if (resources.hasMoreElements()) {
				URL entry = resources.nextElement();

				// XXX not sure if this is needed here
				preventDirectoryMatch(uri, entry);

				return new InputSupplier<InputStream>() {

					@Override
					public InputStream getInput() throws IOException {
						return loader.getResourceAsStream(path);
					}
				};
			}
			else {
				throw new ResourceNotFoundException();
			}
		}
	}

	private void preventDirectoryMatch(URI uri, URL candidate) throws ResourceNotFoundException {
		if (uri != null && candidate != null) {
			String path1 = uri.getPath();
			String path2 = candidate.getPath();
			if (path2.endsWith("/") && !path1.endsWith("/")) {
				throw new ResourceNotFoundException("Found only directory match for resource");
			}
		}
	}

}