org.ambraproject.configuration.WebAppListener.java Source code

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Here is the source code for org.ambraproject.configuration.WebAppListener.java

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/* $HeadURL::                                                                            $
 * $Id$
 *
 * Copyright (c) 2006-2010 by Public Library of Science
 * http://plos.org
 * http://ambraproject.org
 *
 * 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 org.ambraproject.configuration;

import java.net.MalformedURLException;
import java.net.URL;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

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

/**
 * A listener class for web-apps to load a configuration at startup.
 *
 * @author Pradeep Krishnan
 * @author Eric Brown
 */
public class WebAppListener implements ServletContextListener {
    private static Log log = LogFactory.getLog(WebAppListener.class);

    /**
     * Destroy the configuration singleton since this web application is getting un-deployed.
     *
     * @param event the destroyed event
     */
    public void contextDestroyed(ServletContextEvent event) {
        ConfigurationStore.getInstance().unloadConfiguration();
    }

    /**
     * Initialize the configuration singleton since this web application is getting deployed.<p>
     *
     * By default, WebAppListener uses the default ConfigurationStore initialization. This
     * usually means using /etc/.../ambra.xml. This can be overridden by setting the
     * org.ambraproject.configuration system property or webapp context variable to a URL or a name
     * resolvable as a resource.
     *
     * @param event The servlet event associated with initializing this context
     * @throws Error on non-recoverable config load error
     */
    public void contextInitialized(ServletContextEvent event) {
        ServletContext context = event.getServletContext();
        FactoryConfig config = getFactoryConfig(context);

        try {
            URL url;

            // Locate the config url.
            if (config.name.startsWith("/WEB-INF")) {
                url = context.getResource(config.name);

                if (url == null)
                    throw new MalformedURLException("'" + config.name + "' not found in the web-app context");
            } else {
                try {
                    // First see if it is a valid URL
                    url = new URL(config.name);
                } catch (MalformedURLException e) {
                    // Otherwise, load as a resource
                    url = WebAppListener.class.getResource(config.name);
                    if (url == null)
                        throw e;
                }
            }

            // Now load the config
            log.info("Loading '" + url + "' (" + config.name + ") configured via " + config.source);
            ConfigurationStore.getInstance().loadConfiguration(url);

            // Setup an application scope attribute that something like freemarker or struts might use
            context.setAttribute("config", ConfigurationStore.getInstance().getConfiguration());
        } catch (MalformedURLException e) {
            log.fatal(config.name + " defined by " + config.source + " is not a valid URL or resource", e);
            throw new Error("Failed to load configuration", e);
        } catch (ConfigurationException e) {
            log.fatal("Failed to initialize configuration factory.", e);
            throw new Error("Failed to load configuration", e);
        }
    }

    private FactoryConfig getFactoryConfig(ServletContext context) {
        // Allow JVM level property to override everything else
        String name = System.getProperty(ConfigurationStore.CONFIG_URL);

        if (name != null)
            return new FactoryConfig(name, "JVM System property " + ConfigurationStore.CONFIG_URL);

        // Now look for a config specified in web.xml
        name = context.getInitParameter(ConfigurationStore.CONFIG_URL);

        if (name != null)
            return new FactoryConfig(name,
                    "Web-app context initialization parameter " + ConfigurationStore.CONFIG_URL);

        // Return a default
        return new FactoryConfig(ConfigurationStore.DEFAULT_CONFIG_URL, "default");
    }

    private static class FactoryConfig {
        String name;
        String source;

        FactoryConfig(String name, String source) {
            this.name = name;
            this.source = source;
        }
    }
}