com.moss.veracity.core.config.ConfigManager.java Source code

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Here is the source code for com.moss.veracity.core.config.ConfigManager.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.config;

import java.io.File;
import java.io.FileWriter;
import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

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

import com.moss.veracity.core.filemonitor.FileListener;
import com.moss.veracity.core.filemonitor.FileMonitor;

public final class ConfigManager {

    private final Log log = LogFactory.getLog(this.getClass());
    private final JAXBContext jaxbContext;
    private final File file;
    private final FileMonitor monitor;
    private final Object sync = new Object();
    private final List<ConfigListener> listeners = new ArrayList<ConfigListener>();

    private Configuration current;

    public ConfigManager(File file) {

        if (file == null) {
            throw new NullPointerException();
        }

        this.file = file.getAbsoluteFile();

        try {
            jaxbContext = JAXBContext.newInstance(Configuration.class);
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }

        try {
            current = read();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }

        monitor = FileMonitor.monitor(file, 1000);
        monitor.addListener(new ConfigFileListener());
    }

    public Configuration config() {
        synchronized (sync) {
            return current.copy();
        }
    }

    public void updateConfig(Configuration config) {

        synchronized (sync) {
            try {

                if (log.isDebugEnabled()) {
                    log.debug("Updating configuration file: " + file);
                }

                monitor.setPaused(true);

                write(config);

                current = config.copy();
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            } finally {
                monitor.setPaused(false);
            }

            fireChanged(config);
        }
    }

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

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

    public void close() {
        monitor.stop();
    }

    private Configuration read() throws Exception {
        if (file.exists()) {

            if (log.isDebugEnabled()) {
                log.debug("Reading configuration: " + file);
            }

            Unmarshaller u = jaxbContext.createUnmarshaller();
            return (Configuration) u.unmarshal(file);
        } else {

            if (log.isDebugEnabled()) {
                log.debug("Configuration file missing, creating default configuration: " + file);
            }

            Configuration config = new Configuration();
            write(config);
            return config;
        }
    }

    private void write(Configuration config) throws Exception {
        Marshaller m = jaxbContext.createMarshaller();
        m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        m.marshal(config, new FileWriter(file));

        if (monitor != null) {
            monitor.reset();
        }
    }

    private class ConfigFileListener implements FileListener {
        public void fileChanged() {

            synchronized (sync) {

                Configuration config;
                try {
                    config = read();
                } catch (Exception ex) {
                    throw new RuntimeException(ex);
                }

                current = config.copy();

                fireChanged(config);
            }
        }
    }

    private void fireChanged(Configuration config) {
        for (ConfigListener l : listeners) {
            l.configChanged(config);
        }
    }

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

        BasicConfigurator.configure();

        ConfigManager manager = new ConfigManager(new File("test.xml"));

        Thread.sleep(3000l);

        manager.updateConfig(new Configuration());

        Thread.sleep(3000l);

        manager.close();
    }
}