net.sf.ideais.ApplicationManager.java Source code

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Here is the source code for net.sf.ideais.ApplicationManager.java

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/*
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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
     
Copyright (C) 2007 Marco Aurelio Graciotto Silva <magsilva@gmail.com>
*/

package net.sf.ideais;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;

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

import net.sf.ideais.apps.Application;
import net.sf.ideais.util.conf.Configuration;

/**
 * The ApplicationManager controls the loading of application adapter's.
 * Every application is unique (if you try to load an application with the
 * sama configuration, it will return the application previously loaded).
 */
public class ApplicationManager {
    /**
    * Commons Logging instance.
    */
    private static final Log log = LogFactory.getLog(ApplicationManager.class);

    /**
     * Singleton implementation for the ApplicationManager.
     */
    private static ApplicationManager instance;

    /**
     * Applications managed.
     */
    private ArrayList<Application> apps;

    /**
     * Singleton implementation for the ApplicationManager.
     */
    private ApplicationManager() {
        apps = new ArrayList<Application>();
    }

    /**
     * Load an application adapter.
     * 
     * @param clazz The class for the application adapter.
     * @param conf The configuration to be used to load the application adapter.
     * @return The application adapter or null if couldn't load any.
     */
    private Application loadApplication(Class<? extends Application> clazz, Configuration conf) {
        Application app = null;
        log.debug("Loading " + clazz.getName() + " application adapter");

        try {
            Constructor<? extends Application> constructor = clazz.getConstructor(Configuration.class);
            app = constructor.newInstance(conf);
        } catch (NoSuchMethodException e) {
        } catch (InstantiationException e) {
        } catch (IllegalAccessException e) {
        } catch (InvocationTargetException e) {
        }

        if (app == null) {
            log.error("Couldn't load " + clazz.getName() + " application adapter");
        } else {
            log.debug("Loaded application adapter " + clazz.getName());
        }

        return app;
    }

    /**
     * Register an application. We can assure that no duplicated application adapter
     * (same class and configuration) will be registered.
     * 
     * @param app The application to be registered.
     * @return The registered application. If there was an already running application
     * adapter (with the same configuration as app), that application adapter is
     * returned instead of the one given as argument.
     */
    private Application registerApplication(Application app) {
        log.debug("Registering " + app.getClass().getName() + " application adapter");

        for (Application tmp : apps) {
            if (tmp.getId().equals(app.getId())) {
                log.debug("Ignored registration request: " + app.getClass().getName() + " was already registered");
                return tmp;
            }
        }

        apps.add(app);
        log.debug("Registered application adapter " + app.getClass().getName());
        return app;
    }

    private static void startNewInstance() {
        log.info("Loading the application manager");
        instance = new ApplicationManager();
        log.info("Loaded the application manager");
    }

    /**
     * Get the instance of the ApplicationManager.
     */
    public synchronized static ApplicationManager instance() {
        log.info("Getting the application manager");
        if (instance == null) {
            startNewInstance();
        }
        log.info("Got the application manager");
        return instance;
    }

    /**
     * Get an instance of the given application. The ApplicationManager ensures that
     * there's only one application with a given configuration running.
     * 
     * @param clazz The application adapter.
     * @param conf The configuration to be used when loading the application adapter.
     * @return
     */
    public synchronized Application get(Class<? extends Application> clazz, Configuration conf) {
        log.info("Getting adapter for " + clazz.getName());
        Application app = null;

        if (clazz == null) {
            throw new IllegalArgumentException("Invalid application adapter " + clazz);
        }
        app = loadApplication(clazz, conf);

        if (app == null) {
            throw new IllegalArgumentException("Invalid application adapter " + clazz);
        }

        app = registerApplication(app);
        log.info("Got adapter for " + clazz.getName() + " " + app.getVersion() + " at " + app.getId());
        return app;
    }
}