org.datacleaner.extensions.ClassLoaderUtils Maven / Gradle / Ivy

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/**
 * DataCleaner (community edition)
 * Copyright (C) 2014 Free Software Foundation, Inc.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * 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 Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.datacleaner.extensions;

import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.security.AccessController;
import java.security.PrivilegedAction;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A utility class for dealing with {@link ClassLoader}s. The primary focus of
 * this class is to ease with handling the diversity of situations that the
 * application can be deployed to: Embedded in a non-system classloader, a Java
 * Web Start classloader and running in a regular system classloader.
 */
public final class ClassLoaderUtils {

    // to find out if web start is running, use system property
    // http://lopica.sourceforge.net/faq.html#under
    public static final boolean IS_WEB_START = System.getProperty("javawebstart.version") != null;
    private static final Logger logger = LoggerFactory.getLogger(ClassLoaderUtils.class);

    private ClassLoaderUtils() {
        // prevent instantiation
    }

    /**
     * Gets an appropriate classloader for usage when performing classpath
     * lookups and scanning.
     *
     * @return
     */
    public static ClassLoader getParentClassLoader() {
        logger.debug("getParentClassLoader() invoked, web start mode: {}", IS_WEB_START);
        if (IS_WEB_START) {
            return Thread.currentThread().getContextClassLoader();
        } else {
            return ClassLoaderUtils.class.getClassLoader();
        }
    }

    public static ClassLoader createClassLoader(final File[] files) {
        return createClassLoader(files, getParentClassLoader());
    }

    public static ClassLoader createClassLoader(final File[] files, final ClassLoader parentClassLoader) {
        try {
            final URL[] urls = new URL[files.length];
            for (int i = 0; i < urls.length; i++) {
                final URL url = files[i].toURI().toURL();
                logger.debug("Using URL: {}", url);
                urls[i] = url;
            }
            return createClassLoader(urls, parentClassLoader);
        } catch (final MalformedURLException e) {
            throw new IllegalStateException(e);
        }
    }

    public static ClassLoader createClassLoader(final URL[] urls) {
        return createClassLoader(urls, ClassLoaderUtils.getParentClassLoader());
    }

    public static ClassLoader createClassLoader(final URL[] urls, final ClassLoader parentClassLoader) {
        // removing the security manager is necessary for classes in external jar files to have privileges to do
        // eg. system property lookups etc.
        System.setSecurityManager(null);
        return AccessController
                .doPrivileged((PrivilegedAction) () -> new URLClassLoader(urls, parentClassLoader));
    }
}