Plugin.java

/*
 * $Id$
 *
 * Copyright (C) 2003-2015 JNode.org
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library 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 library; If not, write to the Free Software Foundation, Inc., 
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
package org.jnode.plugin;

import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.prefs.Preferences;

import org.jnode.bootlog.BootLogInstance;


/**
 * Abstract plugin class.
 *
 * @author Ewout Prangsma (epr@users.sourceforge.net)
 */
public abstract class Plugin {

    /**
     * The descriptor of this plugin
     */
    private final PluginDescriptor descriptor;
    /**
     * Has this plugin been started?
     */
    private boolean started;
    /**
     * Preferences root for plugins
     */
    private static transient Preferences pluginPrefs;

    /**
     * Initialize a new instance
     *
     * @param descriptor
     */
    public Plugin(PluginDescriptor descriptor) {
        this.descriptor = descriptor;
        this.started = false;
        if (descriptor == null) {
            throw new IllegalArgumentException("descriptor cannot be null");
        }
    }

    /**
     * Gets the descriptor of this plugin
     *
     * @return The descriptor
     */
    public final PluginDescriptor getDescriptor() {
        return descriptor;
    }

    /**
     * Gets the configuration data of this plugin.
     *
     * @return The persistent configuration data.
     */
    public final Preferences getPreferences() {
        if (pluginPrefs == null) {
            final Preferences root;
            root = AccessController
                .doPrivileged(new PrivilegedAction<Preferences>() {
                    public Preferences run() {
                        return Preferences.systemRoot();
                    }
                });
            pluginPrefs = root.node("plugins");
        }
        return pluginPrefs.node(getDescriptor().getId().replace('.', '-'));
    }

    /**
     * Start this plugin
     * To invoke this method, a JNodePermission("startPlugin") is required.
     *
     * @throws PluginException
     */
    public final void start() throws PluginException {
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(PluginSecurityConstants.START_PERM);
        }
        if (!started) {
            if (descriptor.hasCustomPluginClass()) {
                BootLogInstance.get().debug("Starting plugin: " + descriptor.getId());
            }
            started = true;
            try {
                try {
                    startPlugin();
                } finally {
                    descriptor.firePluginStarted();
                }
            } catch (PluginException ex) {
                throw ex;
            } catch (Throwable ex) {
                throw new PluginException(ex);
            }
        }
    }

    /**
     * Stop this plugin.
     * To invoke this method, a JNodePermission("stopPlugin") is required.
     *
     * @throws PluginException
     */
    public final void stop() throws PluginException {
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(PluginSecurityConstants.STOP_PERM);
        }
        if (started) {
            started = false;
            try {
                try {
                    descriptor.firePluginStopped();
                } finally {
                    stopPlugin();
                }
            } catch (PluginException ex) {
                throw ex;
            } catch (Throwable ex) {
                throw new PluginException(ex);
            }
        }
    }

    /**
     * Is this plugin active. A plugin if active between a call to start and stop.
     *
     * @return boolean
     * @see #start()
     * @see #stop()
     */
    public final boolean isActive() {
        return started;
    }

    /**
     * Has this plugin finished its startup work.
     * Most plugins do their start work in the {@link #startPlugin()} method.
     * However, some plugins create thread there to do some work in the background.
     * These plugins should overwrite this method and return true when the startup
     * process is fully finished.
     *
     * @return True if this plugins has fully finished its startup process, false otherwise.
     */
    public boolean isStartFinished() {
        return started;
    }

    /**
     * Actually start this plugin.
     *
     * @throws PluginException
     */
    protected abstract void startPlugin() throws PluginException;

    /**
     * Actually start this plugin.
     *
     * @throws PluginException
     */
    protected abstract void stopPlugin() throws PluginException;
}