JFSLog.java

/*
 * JFileSync
 * Copyright (C) 2002-2007, Jens Heidrich
 *
 * 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 St, Fifth Floor, Boston, MA, 02110-1301, USA
 */
package jfs.conf;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;


/**
 * This class handles log messages (including ERRor messages). Log messages can
 * be send to a log file (e.g., when JFS is started with its GUI) or to any
 * print stream.
 *
 * @author Jens Heidrich
 * @version $Id: JFSLog.java,v 1.7 2007/02/26 18:50:12 heidrich Exp $
 */
public class JFSLog {

    /**
     * The ERRor message log.
     */
    private static final JFSLog ERR = new JFSLog(System.err, JFSConst.ERR_LOG_FILE);

    /**
     * The standard OUTput message log.
     */
    private static final JFSLog OUT = new JFSLog(System.out, JFSConst.OUT_LOG_FILE);

    /**
     * The log message stream to use.
     */
    private final PrintStream printStream;

    /**
     * The file containing all log messages.
     */
    private final File logFile;

    /**
     * The print stream to use for OUTputting log messages.
     */
    private PrintStream currentStream;

    /**
     * Determines whether unread log messages are available.
     */
    private boolean unreadLogMessages = false;

    /**
     * Vector with all oberservers of the configuration object.
     */
    private final List<JFSLogObserver> observers = new ArrayList<>();


    /**
     * Creates a new log. Per default the log messages are OUTputed to the log stream.
     *
     * @param printStream
     * The print stream to use.
     * @param logFileName
     * The log file name to use. The log file is stored in the JFS
     * settings directory (usually '~/.jfs').
     */
    public JFSLog(PrintStream printStream, String logFileName) {
        this.printStream = printStream;
        logFile = new File(JFSConst.HOME_DIR+File.separator+logFileName);
        currentStream = printStream;
    }


    /**
     * Determines whether the log file should be used for OUTputting log messages or the print stream.
     * The log file is located in the JFS settings directory of the users home directory (usually '~/.jfs').
     * The log file and the settings directory are created if they don't exist .
     *
     * @param useLogFile
     * True if and only if the log file should be used.
     */
    public void useLogFile(boolean useLogFile) {
        if (useLogFile) {
            // Redirect error stream to file:
            File home = new File(JFSConst.HOME_DIR);

            if (!home.exists()) {
                home.mkdir();
            }

            try {
                if (!logFile.exists()) {
                    logFile.createNewFile();
                }
                currentStream = new PrintStream(new FileOutputStream(logFile));
            } catch (IOException e) {
                System.err.println(e);
            }
        } else {
            currentStream = printStream;
        }
    }


    /**
     * Resets the log file in the JFS configuration directory to which log
     * messages are sent to. It is deleted and created from scratch if it
     * already exists. The log stream is redirected to the newly created log
     * file afterwards.
     */
    public void resetLogFile() {
        unreadLogMessages = false;

        // Delete previous log file and create new one:
        if (logFile.exists()) {
            logFile.delete();
        }

        useLogFile(true);
    }


    /**
     * Returns the the log file URL.
     *
     * @return The log file URL.
     * @throws MalformedURLException
     * Thrown in case of a malformed URL.
     */
    public URL getLogURL() throws MalformedURLException {
        return logFile.toURI().toURL();
    }


    /**
     * Returns the current log stream to OUTput log messages to. If the stream
     * is requested, it is assumed that new log messages are written to the
     * stream, so that the log object has unread log messages.
     *
     * @return The log stream.
     */
    public PrintStream getStream() {
        synchronized (this) {
            unreadLogMessages = true;
            fireUpdate();
            return currentStream;
        }
    }


    /**
     * Returns whether unread log messages are available.
     *
     * @return True if and only if new messages are available.
     */
    public boolean hasUnreadLogMessages() {
        return unreadLogMessages;
    }


    /**
     * Determines that the log has no unread log messages.
     */
    public void setLogMessagesRead() {
        unreadLogMessages = false;
        fireUpdate();
    }


    /**
     * Attaches an additional observer.
     *
     * @param observer
     * The new observer.
     */
    public final void attach(JFSLogObserver observer) {
        observers.add(observer);
        observer.update(this);
    }


    /**
     * Detaches an existing observer.
     *
     * @param observer
     * An old observer.
     */
    public final void detach(JFSLogObserver observer) {
        observers.remove(observer);
    }


    /**
     * Updates the observers.
     */
    private final void fireUpdate() {
        for (JFSLogObserver observer : observers) {
            observer.update(this);
        }
    }


    /**
     * Returns the ERRor message log.
     *
     * @return The log object.
     */
    public static JFSLog getErr() {
        return ERR;
    }


    /**
     * Returns the standard OUTput message log.
     *
     * @return The log object.
     */
    public static JFSLog getOut() {
        return OUT;
    }

}