| gvSIG desktop 1

/* gvSIG. Geographic Information System of the Valencian Government

 *

 * Copyright (C) 2007-2008 Infrastructures and Transports Department

 * of the Valencian Government (CIT)

 * 

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 * 

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 * 

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, 

 * MA  02110-1301, USA.

 * 

 */

/*

 * AUTHORS (In addition to CIT):

 * 2009 {DiSiD Technologies}  {{Task}}

 */

package org.gvsig.tools.util.impl;

import java.lang.reflect.Method;

import java.util.Iterator;

import java.util.LinkedHashSet;

import java.util.Set;

import org.gvsig.tools.util.ServiceLoader;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

/**

 * Implementation which uses reflection to try to use first the standard JDK

 * utilities to load service implementation classes, which are available since

 * JDK 1.6. If it fails or the JDK used is < 1.6, the old mechanism based on the

 * usage of internal sun classes is used.

 * <p>

 * To register your implementations classes for a service, use the mechanism

 * explained in the Java JAR file specification for the JDK version you are

 * using:

 * <ul>

 * <li><a href=

 * "http://java.sun.com/j2se/1.4.2/docs/guide/jar/jar.html#Service%20Provider"

 * >JDK 1.4</a></li>

 * <li><a href=

 * "http://java.sun.com/j2se/1.5.0/docs/guide/jar/jar.html#Service%20Provider"

 * >JDK 1.5</a></li>

 * <li><a href="http://java.sun.com/javase/6/docs/technotes/guides/jar/jar.html#Service%20Provider"

 * >JDK 1.6</a></li>

 * </ul>

 * </p>

 * 

 * 

 * @author <a href="mailto:cordinyana@gvsig.org">C?sar Ordi?ana</a>

 */

public class DefaultServiceLoader implements ServiceLoader {

        private static final Logger LOG = LoggerFactory

                        .getLogger(DefaultServiceLoader.class);

        public Set load(Class serviceClass) {

                return load(serviceClass, null);

        }

        public Set load(Class serviceClass, ClassLoader classLoader) {

                try {

                        return postJDK16Load(serviceClass, classLoader);

                } catch (Exception e) {

                        LOG.debug("Could not use the JDK >= 1.6 utility classes "

                                        + "to load the {} implementation classes, "

                                        + "we may be running on a JDK < 1.6, so I will try "

                                        + "to use the JDK < 1.6 sun.misc.Service class",

                                        serviceClass);

                        LOG.trace("The exception thrown is: ", e);

                }

                try {

                        return preJDK16Load(serviceClass, classLoader);

                } catch (Exception e) {

                        LOG

                                        .error("Error finding available " + serviceClass

                                                        + " objects", e);

                }

                return null;

        }

        /**

         * Load the classes using the pre JDK 1.6 sun utilities.

         */

        private Set preJDK16Load(Class serviceClass, ClassLoader classLoader)

                        throws Exception {

                LOG.info("Using the sun.misc.Service to load the {} {}", serviceClass,

                                serviceClass.isInterface() ? "implementations" : "extensions");

                // Use reflection to call the internal Sun JDK class and avoid

                // compiler errors in eclipse

                Class serviceClazz = Class.forName("sun.misc.Service");

                if (serviceClazz == null) {

                        LOG.error("Could not load Class sun.misc.Service "

                                        + "using reflection");

                        return null;

                }

                Method providersMethod = null;

                if (classLoader == null) {

                        providersMethod = serviceClazz.getMethod("providers",

                                        new Class[] { Class.class });

                } else {

                        providersMethod = serviceClazz.getMethod("providers", new Class[] {

                                        Class.class, ClassLoader.class });

                }

                Iterator iterator = null;

                if (classLoader == null) {

                        iterator = (Iterator) providersMethod.invoke(null,

                                        new Object[] { serviceClass });

                } else {

                        iterator = (Iterator) providersMethod.invoke(null, new Object[] {

                                        serviceClass, classLoader });

                }

                if (iterator == null) {

                        LOG.debug("Empty {} objects iterator returned by the "

                                        + "sun.misc.Service.providers method", serviceClass);

                        return null;

                }

                Set services = new LinkedHashSet();

                for (; iterator.hasNext();) {

                        services.add(iterator.next());

                }

                return services;

        }

        /**

         * Load the classes using the JDK 1.6 standard utilities.

         */

        private Set postJDK16Load(Class serviceClass, ClassLoader classLoader)

                        throws Exception {

                LOG.info("Using the java.util.ServiceLoader to load " + "the {} {}",

                                serviceClass, serviceClass.isInterface() ? "implementations"

                                                : "extensions");

                // Use reflection to call the JDK >= 1.6 utility classes and being

                // able to compile with JDK 1.4 or 1.5

                Class serviceLoaderClazz = Class.forName("java.util.ServiceLoader");

                Method loadMethod = null;

                if (classLoader == null) {

                        loadMethod = serviceLoaderClazz.getMethod("load",

                                        new Class[] { Class.class });

                } else {

                        loadMethod = serviceLoaderClazz.getMethod("load", new Class[] {

                                        Class.class, ClassLoader.class });

                }

                Object serviceLoader = null;

                if (classLoader == null) {

                        serviceLoader = loadMethod.invoke(null,

                                        new Object[] { serviceClass });

                } else {

                        serviceLoader = loadMethod.invoke(null, new Object[] {

                                        serviceClass, classLoader });

                }

                if (serviceLoader == null) {

                        LOG.error("Could not load a ServiceLoader to load {} objects",

                                        serviceClass);

                        return null;

                }

                Method iteratorMethod = serviceLoaderClazz.getMethod("iterator", null);

                Iterator iterator = (Iterator) iteratorMethod.invoke(serviceLoader,

                                null);

                if (iterator == null) {

                        LOG.debug(

                                        "java.util.ServiceLoader of {} returned an empty iterator",

                                        serviceClass);

                        return null;

                }

                Set services = new LinkedHashSet();

                for (; iterator.hasNext();) {

                        services.add(iterator.next());

                }

                return services;

        }

}