eu.esdihumboldt.util.resource.Resources.java Source code

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Here is the source code for eu.esdihumboldt.util.resource.Resources.java

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/*
 * 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;

import java.io.InputStream;
import java.net.URI;
import java.util.HashMap;
import java.util.Map;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.Multimap;

import eu.esdihumboldt.util.io.InputSupplier;
import eu.esdihumboldt.util.resource.internal.ResolverConfiguration;
import eu.esdihumboldt.util.resource.internal.ResolverExtension;

/**
 * Utility methods for the resource extensions.
 * 
 * @author Simon Templer
 */
public abstract class Resources implements ResourcesConstants {

    /**
     * Resource type mapped to host name mapped to resource resolver
     */
    private static Map<String, Multimap<String, ResourceResolver>> resolvers;

    /**
     * Try resolving an URI for a given resource type.
     * 
     * @param uri the URI to the resource
     * @param resourceType the resource type, <code>null</code> for any resource
     *            type
     * @return an input supplier for the resource or <code>null</code> if it was
     *         not found through resource resolvers
     */
    public static final InputSupplier<? extends InputStream> tryResolve(URI uri, String resourceType) {
        init();

        if (resourceType != null) {
            Multimap<String, ResourceResolver> typeResolvers = resolvers.get(resourceType);
            if (typeResolvers != null) {
                return tryResolve(typeResolvers, uri);
            }
        } else {
            for (Multimap<String, ResourceResolver> typeResolver : resolvers.values()) {
                InputSupplier<? extends InputStream> input = tryResolve(typeResolver, uri);
                if (input != null) {
                    // return first match found
                    return input;
                }
            }
        }

        return null;
    }

    private static InputSupplier<? extends InputStream> tryResolve(Multimap<String, ResourceResolver> typeResolvers,
            URI uri) {
        for (ResourceResolver resolver : typeResolvers.get(uri.getHost())) {
            try {
                return resolver.resolve(uri);
            } catch (ResourceNotFoundException e) {
                // ignore
            }
        }

        return null;
    }

    private static synchronized void init() {
        if (resolvers == null) {
            resolvers = new HashMap<String, Multimap<String, ResourceResolver>>();

            // register resolvers
            for (ResolverConfiguration resolverConf : ResolverExtension.getInstance().getElements()) {
                String resourceType = resolverConf.getResourceTypeId();

                Multimap<String, ResourceResolver> typeResolvers = resolvers.get(resourceType);
                if (typeResolvers == null) {
                    typeResolvers = HashMultimap.create();
                    resolvers.put(resourceType, typeResolvers);
                }

                for (String host : resolverConf.getHosts()) {
                    typeResolvers.put(host, resolverConf.getResourceResolver());
                }
            }
        }
    }

}