it.cnr.icar.eric.server.common.AbstractFactory.java Source code

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Here is the source code for it.cnr.icar.eric.server.common.AbstractFactory.java

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/*
 * ====================================================================
 * This file is part of the ebXML Registry by Icar Cnr v3.2 
 * ("eRICv32" in the following disclaimer).
 *
 * "eRICv32" 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 3 of the License, or
 * (at your option) any later version.
 *
 * "eRICv32" 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 Version 3
 * along with "eRICv32".  If not, see <http://www.gnu.org/licenses/>.
 *
 * eRICv32 is a forked, derivative work, based on:
 *    - freebXML Registry, a royalty-free, open source implementation of the ebXML Registry standard,
 *      which was published under the "freebxml License, Version 1.1";
 *   - ebXML OMAR v3.2 Edition, published under the GNU GPL v3 by S. Krushe & P. Arwanitis.
 * 
 * All derivative software changes and additions are made under
 *
 * Copyright (C) 2013 Ing. Antonio Messina <messina@pa.icar.cnr.it>
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the freebxml Software Foundation.  For more
 * information on the freebxml Software Foundation, please see
 * "http://www.freebxml.org/".
 *
 * This product includes software developed by the Apache Software
 * Foundation (http://www.apache.org/).
 *
 * ====================================================================
 */
package it.cnr.icar.eric.server.common;

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

import it.cnr.icar.eric.server.util.ServerResourceBundle;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

/**
 * Creates an instance of a type specified by a registry property if
 * the instance does not yet exist.  This is a common operation,
 * although the property name, the variable that refers to the object
 * instance, and the type of the object instance vary each time.
 *
 * @author  Tony Graham
 */
public abstract class AbstractFactory {
    private static final Log log = LogFactory.getLog(AbstractFactory.class.getName());

    /**
     * Get an instance of the class specified by the value of the
     * registry property specified by <code>propertyName</code> only
     * if the current value of the instance is <code>null</code>.
     *
     * @param propertyName name of registry property specifying class name
     * @param object variable to hold the instance
     * @return an instance of the specified class
     */
    protected synchronized Object getInstance(String propertyName, Object object) {
        if (object == null) {
            try {
                String pluginClass = RegistryProperties.getInstance().getProperty(propertyName);

                object = createPluginInstance(pluginClass);
            } catch (Exception e) {
                String errmsg = ServerResourceBundle.getInstance()
                        .getString("message.AbstractFactoryCannotInstantiatePlugin", new Object[] { propertyName });
                log.error(errmsg, e);
            }
        }

        return object;
    }

    /**
     * Creates the instance of the pluginClass
     *
     * @param pluginClass class name of instance to create
     * @return an instance of the specified class
     * @exception Exception if an error occurs
     */
    protected Object createPluginInstance(String pluginClass) throws Exception {
        Object plugin = null;

        if (log.isDebugEnabled()) {
            log.debug("pluginClass = " + pluginClass);
        }

        Class<?> theClass = Class.forName(pluginClass);

        //try to invoke constructor using Reflection, 
        //if this fails then try invoking getInstance()
        try {
            Constructor<?> constructor = theClass.getConstructor((java.lang.Class[]) null);
            plugin = constructor.newInstance(new Object[0]);
        } catch (Exception e) {
            log.warn(ServerResourceBundle.getInstance()
                    .getString("message.NoAccessibleConstructorInvokingGetInstanceInstead"));

            Method factory = theClass.getDeclaredMethod("getInstance", (java.lang.Class[]) null);
            plugin = factory.invoke(null, new Object[0]);
        }

        return plugin;
    }
}