source: trunk/quest-plugin-core/src/main/java/de/ugoe/cs/quest/plugin/PluginLoader.java @ 766

package de.ugoe.cs.quest.plugin;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FilenameFilter;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;
import java.util.jar.JarInputStream;
import java.util.jar.Manifest;

/**
 * <p>
 * This class provides the functionality to load QUEST plug-ins from a
 * pre-defined folder.
 * </p>
 * 
 * @author Steffen Herbold
 * @version 1.0
 */
public class PluginLoader {

        /**
         * <p>
         * Handle of the plug-in directory.
         * </p>
         */
        private final File pluginDir;

        /**
         * <p>
         * Collection of the loaded plug-ins.
         * </p>
         */
        private final Collection<QuestPlugin> plugins;

        /**
         * <p>
         * Constructor. Creates a new PluginLoader that can load plug-ins the
         * defined directory.
         * </p>
         * 
         * @param pluginDir
         *            handle of the directory; in case the handle is
         *            <code>null</code> or does not describe a directory, an
         *            {@link IllegalArgumentException} is thrown
         */
        public PluginLoader(File pluginDir) {
                if (pluginDir == null) {
                        throw new IllegalArgumentException(
                                        "Parameter pluginDir must not be null!");
                }
                if (!pluginDir.isDirectory()) {
                        throw new IllegalArgumentException("File " + pluginDir.getPath()
                                        + " is not a directory");
                }
                this.pluginDir = pluginDir;
                plugins = new LinkedList<QuestPlugin>();
        }

        /**
         * <p>
         * Loads plug-ins from {@link #pluginDir}.
         * </p>
         * 
         * @throws PluginLoaderException
         *             thrown if there is a problem loading a plug-in or updating
         *             the classpath
         */
        public void load() throws PluginLoaderException {
                File[] jarFiles = pluginDir.listFiles(new FilenameFilter() {
                        @Override
                        public boolean accept(File dir, String name) {
                                return checkNameConformity(name);
                        }
                });

                for (File jarFile : jarFiles) {
                        updateClassLoader(jarFile);

                        String pluginName = jarFile.getName().split("-")[2];
                        String pluginClassName = "de.ugoe.cs.quest.plugin." + pluginName
                                        + "." + pluginName.toUpperCase() + "Plugin";

                        Class<?> pluginClass = null;
                        try {
                                pluginClass = Class.forName(pluginClassName);
                        } catch (ClassNotFoundException e) {
                                throw new PluginLoaderException("No class '" + pluginClassName
                                                + "' found in " + pluginDir + "/" + jarFile.getName());
                        }
                        try {
                                QuestPlugin pluginObject = (QuestPlugin) pluginClass
                                                .newInstance();
                                plugins.add(pluginObject);
                        } catch (InstantiationException e) {
                                throw new PluginLoaderException("Could not instantiate "
                                                + pluginClassName);
                        } catch (IllegalAccessException e) {
                                throw new PluginLoaderException("Could not access "
                                                + pluginClassName);
                        } catch (ClassCastException e) {
                                throw new PluginLoaderException("Class " + pluginClassName
                                                + " not instance of QuestPlugin");
                        }
                }
        }

        /**
         * <p>
         * Retrieves the classpath from a Jar file's MANIFEST.
         * </p>
         * 
         * @throws IOException
         * @throws FileNotFoundException
         */
        protected String[] getClassPathFromJar(File jarFile) {
                String[] classPath;

                JarInputStream jarInputStream = null;
                try {
                        jarInputStream = new JarInputStream(new FileInputStream(jarFile));
                } catch (FileNotFoundException e) {
                        throw new AssertionError(
                                        "FileNotFoundException should be impossible!");
                } catch (IOException e) {
                        throw new PluginLoaderException(e);
                }

                Manifest manifest = jarInputStream.getManifest();

                String jarClassPath = manifest.getMainAttributes().getValue(
                                "Class-Path");

                if (jarClassPath != null) {
                        String[] jarClassPathElements = jarClassPath.split(" ");
                        classPath = new String[jarClassPathElements.length];
                        for (int i = 0; i < jarClassPathElements.length; i++) {
                                classPath[i] = "file:"
                                                + jarFile.getParentFile().getAbsolutePath() + "/"
                                                + jarClassPathElements[i];
                        }
                        try {
                                jarInputStream.close();
                        } catch (IOException e) {
                                throw new PluginLoaderException(e);
                        }
                } else {
                        classPath = new String[] {};
                }
                return classPath;
        }

        /**
         * <p>
         * Updates the classpath of the {@link ClassLoader} to include the plug-in
         * jar as well as further libraries required by the plug-in jar as defined
         * in the <code>Class-Path</code> section of its manifest.
         * </p>
         * 
         * @param jarFile
         *            handle of the plug-in jar file
         * @throws PluginLoaderException
         *             thrown if there is a problem updating the class loader or
         *             loading the plug-in jar
         */
        private void updateClassLoader(File jarFile) throws PluginLoaderException {
                String[] classPath = getClassPathFromJar(jarFile);
                URLClassLoader classLoader = (URLClassLoader) ClassLoader
                                .getSystemClassLoader();
                Method method;

                try {
                        method = URLClassLoader.class.getDeclaredMethod("addURL",
                                        new Class[] { URL.class });
                } catch (SecurityException e) {
                        throw new PluginLoaderException(
                                        "addURL method of URLClassLoader not accessible via reflection.");
                } catch (NoSuchMethodException e) {
                        throw new AssertionError(
                                        "URLClassLoader does not have addURL method. Should be impossible!!");
                }
                method.setAccessible(true);

                try {
                        method.invoke(
                                        classLoader,
                                        new Object[] { new URL("file:" + jarFile.getAbsoluteFile()) });
                        for (String element : classPath) {
                                method.invoke(classLoader, new Object[] { new URL(element) });
                        }
                } catch (IllegalArgumentException e) {
                        throw new AssertionError(
                                        "Illegal arguments for addURL method. Should be impossible!!");
                } catch (MalformedURLException e) {
                        throw new PluginLoaderException(e);
                } catch (IllegalAccessException e) {
                        throw new PluginLoaderException(
                                        "addURL method of URLClassLoader not accessible via reflection.");
                } catch (InvocationTargetException e) {
                        throw new PluginLoaderException(e);
                }
        }

        /**
         * <p>
         * Checks if the name of a file indicates that it defines a QUEST plug-in.
         * The structure of valid plug-in filenames is
         * <code>quest-plugin-%PLUGIN_NAME%-version.jar</code>, where
         * <code>%PLUGIN_NAME%</code> is replaced by the name of the plug-in. Note
         * that plug-in names must not contain any dashes.
         * </p>
         * 
         * @param filename
         *            filename that is checked
         * @return true if filename matches pattern of QUEST plug-in; false
         *         otherwise
         */
        protected boolean checkNameConformity(String filename) {
                if (filename == null) {
                        return false;
                }
                return filename.startsWith("quest-plugin-") && !filename.startsWith("quest-plugin-core")
                                &&
                                ((filename.split("-").length == 4 && filename.endsWith(".jar")) ||
                                  filename.split("-").length == 5 && filename.endsWith("SNAPSHOT.jar"));
        }
        
        public Collection<QuestPlugin> getPlugins() {
                return Collections.unmodifiableCollection(plugins);
        }
}