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package org.webharvest.utils;

import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.webharvest.exception.PluginException;

/**
 * Class loading utility - used for loading JDBC driver classes and plugin
 * classes.
 */
public final class ClassLoaderUtil {

    private static final Logger LOG =
        LoggerFactory.getLogger(ClassLoaderUtil.class);

    /**
     * class loader that includes all JAR libraries in the working
     * folder of the application.
     */
    private static URLClassLoader rootClassLoader = null;

    /**
     * Prevents against instantiation of utility class.
     */
    private ClassLoaderUtil() {
    }

    /**
     * Lists all JARs in the working folder (folder of WebHarvest executable)
     */
    private static void defineRootLoader() {
        List urls = new ArrayList();
        String rootDirPath = new File("").getAbsolutePath();

        try {
            urls.add(new File("").toURI().toURL());
        } catch (MalformedURLException e) {
            LOG.error("Cannot define root loader", e);
        }

        // add all JAR files from the root folder to the class path
        File[] entries = new File(rootDirPath).listFiles();
        if (entries != null) {
            for (int f = 0; f < entries.length; f++) {
                File entry = entries[f];
                if (entry != null && !entry.isDirectory() && isJar(entry)) {
                    try {
                        String jarAbsolutePath = entry.getAbsolutePath();
                        urls.add(new URL("jar:file://" + jarAbsolutePath.replace('\\', '/') + "!/"));
                    } catch (MalformedURLException e) {
                        LOG.error("Cannot define root loader", e);
                    }
                }
            }
        }

        URL[] urlsArray = new URL[urls.size()];
        for (int i = 0; i < urls.size(); i++) {
            urlsArray[i] = (URL) urls.get(i);
        }

        rootClassLoader = new URLClassLoader(urlsArray,
                ClassLoaderUtil.class.getClassLoader());
    }

    private static boolean isJar(final File file) {
        return file.getName().toLowerCase().endsWith(".jar");
    }

    public static Class< ? > getPluginClass(String fullClassName)
            throws PluginException {
        if (rootClassLoader == null) {
            defineRootLoader();
        }
        try {
            // FIXME: http://stackoverflow.com/questions/11273303/java-classloader-dilemma
            return Class.forName(fullClassName, true, rootClassLoader);
        } catch (ClassNotFoundException e) {
            throw new PluginException("Error finding plugin class \""
                    + fullClassName + "\": " + e.getMessage(), e);
        } catch (NoClassDefFoundError e) {
            throw new PluginException("Error finding plugin class \""
                    + fullClassName + "\": " + e.getMessage(), e);
        }
    }
}