URLConfigurationProvider.java

/**
 * Copyright 2012 Sven Diedrichsen 
 * 
 * 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 de.jollyday.configuration.impl;

import java.io.InputStream;
import java.net.URL;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;

import de.jollyday.configuration.ConfigurationProvider;

/**
 * An {@link ConfigurationProvider} implementation which reads a list of URLs
 * provided by the system property 'de.jollyday.config.urls' in order they are
 * provided into a {@link Properties} instance.
 * 
 * @author Sven Diedrichsen
 */
public class URLConfigurationProvider implements ConfigurationProvider {

	private static final Logger LOG = Logger
			.getLogger(URLConfigurationProvider.class.getName());

	/**
	 * Returns the properties by reading from the URLs provided by the system
	 * property 'de.jollyday.config.urls'.
	 */
	@Override
	public Properties getProperties() {
		Properties properties = new Properties();
		Properties systemProps = System.getProperties();
		String configURLs = systemProps.getProperty(CONFIG_URLS_PROPERTY);
		if (configURLs != null) {
			String[] strConfigURLs = configURLs.split(",");
			if (strConfigURLs != null) {
				for (String strURL : strConfigURLs) {
					readPropertiesFromURL(properties, strURL);
				}
			}
		}
		return properties;
	}

	private void readPropertiesFromURL(Properties properties, String strURL) {
		if (strURL == null || "".equals(strURL))
			return;
		InputStream inputStream = null;
		try {
			URL configURL = new URL(strURL.trim());
			inputStream = configURL.openStream();
			properties.load(inputStream);
		} catch (Exception e) {
			LOG.log(Level.WARNING, "Cannot read configuration from '" + strURL
					+ "'.", e);
		} finally {
			closeStreamFromURL(strURL, inputStream);
		}
	}

	private void closeStreamFromURL(String strURL, InputStream inputStream) {
		if (inputStream != null) {
			try {
				inputStream.close();
			} catch (Exception e) {
				LOG.warning("Cannot close stream for configuration URL "
						+ strURL + ".");
			}
		}
	}

}