com.moss.veracity.core.filemonitor.FileMonitor.java Source code

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Here is the source code for com.moss.veracity.core.filemonitor.FileMonitor.java

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/**
 * Copyright (C) 2013, Moss Computing Inc.
 *
 * This file is part of veracity.
 *
 * veracity 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, or (at your option)
 * any later version.
 *
 * veracity 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 veracity; see the file COPYING.  If not, write to the
 * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301 USA.
 *
 * Linking this library statically or dynamically with other modules is
 * making a combined work based on this library.  Thus, the terms and
 * conditions of the GNU General Public License cover the whole
 * combination.
 *
 * As a special exception, the copyright holders of this library give you
 * permission to link this library with independent modules to produce an
 * executable, regardless of the license terms of these independent
 * modules, and to copy and distribute the resulting executable under
 * terms of your choice, provided that you also meet, for each linked
 * independent module, the terms and conditions of the license of that
 * module.  An independent module is a module which is not derived from
 * or based on this library.  If you modify this library, you may extend
 * this exception to your version of the library, but you are not
 * obligated to do so.  If you do not wish to do so, delete this
 * exception statement from your version.
 */
package com.moss.veracity.core.filemonitor;

import java.io.File;
import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.log4j.BasicConfigurator;

public final class FileMonitor {

    public static FileMonitor monitor(File file, long interval) {
        return new FileMonitor(file, interval);
    }

    private final Log log = LogFactory.getLog(this.getClass());
    private final Object sync = new Object();
    private final List<FileListener> listeners = new ArrayList<FileListener>();
    private final Timer timer;
    private final File file;

    private boolean exists = false;
    private long lastModified = 0;
    private boolean paused = false;

    private FileMonitor(File file, long interval) {
        this.file = file.getAbsoluteFile();

        reset();

        timer = new Timer(true);
        timer.scheduleAtFixedRate(new MonitorTask(), 0, interval);
    }

    public void addListener(FileListener l) {
        synchronized (sync) {
            listeners.add(l);
        }
    }

    public void removeListener(FileListener l) {
        synchronized (sync) {
            listeners.remove(l);
        }
    }

    public void setPaused(boolean paused) {
        synchronized (sync) {
            this.paused = paused;
            if (!paused) {
                sync.notify();
            }
        }
    }

    public void reset() {
        synchronized (sync) {

            if (log.isDebugEnabled()) {
                log.debug("Accepting current state of this file as its unchanged state: " + file);
            }

            exists = file.exists();
            lastModified = file.lastModified();
        }
    }

    public void stop() {

        if (log.isDebugEnabled()) {
            log.debug("Stopping file monitor, file no longer monitored: " + file);
        }

        timer.cancel();
    }

    private class MonitorTask extends TimerTask {
        public void run() {
            delta();
        }
    }

    private void delta() {
        synchronized (sync) {

            if (paused) {

                if (log.isDebugEnabled()) {
                    log.debug("File monitor paused");
                }

                try {
                    sync.wait();
                } catch (InterruptedException ex) {
                    if (log.isWarnEnabled()) {
                        log.warn("Interrupted while waiting for resume", ex);
                    }
                }

                if (log.isDebugEnabled()) {
                    log.debug("File monitor resuming");
                }
            }

            if (!exists && file.exists()) {

                if (log.isDebugEnabled()) {
                    log.debug("Detected creation of file: " + file);
                }

                fireChanged();
                reset();
            } else if (exists && !file.exists()) {

                if (log.isDebugEnabled()) {
                    log.debug("Detected deletion of file: " + file);
                }

                fireChanged();
                reset();
            } else if (lastModified != file.lastModified()) {

                if (log.isDebugEnabled()) {
                    log.debug("Detected modification of file: " + file);
                }

                fireChanged();
                reset();
            }
        }
    }

    private void fireChanged() {
        for (FileListener l : listeners) {
            try {
                l.fileChanged();
            } catch (Exception ex) {
                if (log.isErrorEnabled()) {
                    log.error("Notification failed", ex);
                } else {
                    ex.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) throws Exception {

        BasicConfigurator.configure();

        FileMonitor m = FileMonitor.monitor(new File("pom.xml"), 1000);
        m.addListener(new FileListener() {
            public void fileChanged() {
                System.out.println("Changed");
            }
        });

        m.setPaused(true);

        Thread.sleep(5000l);

        m.setPaused(false);

        Thread.sleep(10000000l);
    }
}