com.google.code.jconfig.factory.ConfigurationPluginFactory.java Source code

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Here is the source code for com.google.code.jconfig.factory.ConfigurationPluginFactory.java

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/*
 * @(#)ConfigurationPluginFactory.java          Data: 27/set/2011 
 *
 *
 * Copyright 2011 Gabriele Fedeli
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package com.google.code.jconfig.factory;

import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.FutureTask;

import org.apache.commons.lang3.ClassUtils;
import org.apache.log4j.Logger;

import com.google.code.jconfig.annotation.Cacheable;
import com.google.code.jconfig.exception.PluginInstantiationException;
import com.google.code.jconfig.reader.plugins.IConfigurationPlugin;

/**
 * <p>
 *    Factory for the custom plugin creation.
 * </p>
 *
 * @author Gabriele Fedeli (gabriele.fedeli@gmail.com)
 */
public abstract class ConfigurationPluginFactory {

    private static ConcurrentHashMap<String, FutureTask<IConfigurationPlugin<?>>> cache = new ConcurrentHashMap<String, FutureTask<IConfigurationPlugin<?>>>();
    private static Logger logger = Logger.getLogger(ConfigurationPluginFactory.class);

    /**
     * <p>
     *    Returns a plugin instance of type <em>classname</em>.
     * </p>
     * 
     * <p>
     *    If the implementation class use the {@link Cacheable} annotation, it
     *    will be cached for future reuse otherwise a new instance will be
     *    created at every request.
     * </p>
     * 
     * @param classname the full name of an instance of
     *                  {@link IConfigurationPlugin}.
     * @return the plugin instance.
     * @throws PluginInstantiationException
     */
    public static IConfigurationPlugin<?> getPlugin(final String classname) throws PluginInstantiationException {

        try {
            if (ClassUtils.getClass(classname).getAnnotation(Cacheable.class) == null) {
                logger.debug("Plugin <" + classname + "> is not cacheable. Creating a new one.");
                return (IConfigurationPlugin<?>) Class.forName(classname).newInstance();
            }
        } catch (Exception e) {
            throw new PluginInstantiationException(e.getMessage(), e);
        }

        // cacheable plugin
        FutureTask<IConfigurationPlugin<?>> theTask = cache.get(classname);
        if (theTask == null) {
            logger.debug("No plugin of class <" + classname + "> available. Creatine a new one.");
            Callable<IConfigurationPlugin<?>> eval = new Callable<IConfigurationPlugin<?>>() {

                public IConfigurationPlugin<?> call() throws Exception {
                    IConfigurationPlugin<?> plugin = (IConfigurationPlugin<?>) Class.forName(classname)
                            .newInstance();
                    return plugin;
                }
            };

            FutureTask<IConfigurationPlugin<?>> thePluginExec = new FutureTask<IConfigurationPlugin<?>>(eval);
            theTask = cache.putIfAbsent(classname, thePluginExec);
            if (theTask == null) {
                theTask = thePluginExec;
                theTask.run();
            }
            logger.debug("New plugin of class <" + classname + "> ready to be used and cached.");
        } else {
            logger.debug("Plugin of class <" + classname + "> available in cache. Using the cached one.");
        }

        try {
            return theTask.get();
        } catch (Exception e) {
            throw new PluginInstantiationException(e.getMessage(), e);
        } finally {
            logger.debug("plugin cache size: " + cache.size() + " - cache detail: " + cache);
        }
    }
}