PropertiesManager.java

package org.caudexorigo.conf;

import java.io.InputStream;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Properties;
import java.util.ResourceBundle;

//----------------------------------------------------------------------------
/**
 * A simple class for loading java.util.Properties backed by .properties files deployed as classpath resources. See individual methods for details.
 * 
 * @author (C) <a href="http://www.javaworld.com/columns/jw-qna-index.shtml">Vlad Roubtsov </a>, 2003
 * @author <a href="mailto:luis.neves@gmail.com">Luis Neves</a>
 */

public class PropertiesManager
{

	private static final boolean LOAD_AS_RESOURCE_BUNDLE = false;

	private static final String SUFFIX = ".properties";

	private static final boolean THROW_ON_LOAD_FAILURE = true;

	private Properties props;

	/**
	 * A convenience overload of {@link #loadProperties(String, ClassLoader)}that uses the current thread's context classloader.
	 */
	public PropertiesManager(final String name)
	{
		this(name, Thread.currentThread().getContextClassLoader());
	}

	/**
	 * Looks up a resource named 'name' in the classpath. The resource must map to a file with .properties extention. The name is assumed to be absolute and can use either "/" or "." for package segment separation with an optional leading "/" and optional ".properties" suffix. Thus, the following names refer to the same resource:
	 * 
	 * <pre>
	 * 
	 * 
	 * 
	 *         some.pkg.Resource
	 *         some.pkg.Resource.properties
	 *         some/pkg/Resource
	 *         some/pkg/Resource.properties
	 *         /some/pkg/Resource
	 *         /some/pkg/Resource.properties
	 * 
	 * 
	 * 
	 * </pre>
	 * 
	 * @param name
	 *            classpath resource name [may not be null]
	 * @param loader
	 *            classloader through which to load the resource [null is equivalent to the application loader]
	 * 
	 * @return resource converted to java.util.Properties [may be null if the resource was not found and THROW_ON_LOAD_FAILURE is false]
	 * @throws IllegalArgumentException
	 *             if the resource was not found and THROW_ON_LOAD_FAILURE is true
	 */
	public PropertiesManager(String name, ClassLoader loader)
	{
		if (name == null)
			throw new IllegalArgumentException("null input: name");

		if (name.startsWith("/"))
			name = name.substring(1);

		if (name.endsWith(SUFFIX))
			name = name.substring(0, name.length() - SUFFIX.length());

		Properties result = null;

		InputStream in = null;
		try
		{
			if (loader == null)
				loader = ClassLoader.getSystemClassLoader();

			if (LOAD_AS_RESOURCE_BUNDLE)
			{
				name = name.replace('/', '.');

				// Throws MissingResourceException on lookup failures:
				final ResourceBundle rb = ResourceBundle.getBundle(name, Locale.getDefault(), loader);

				result = new Properties();
				for (Enumeration<String> keys = rb.getKeys(); keys.hasMoreElements();)
				{
					final String key = keys.nextElement();
					final String value = rb.getString(key);

					result.put(key, value);
				}
			}
			else
			{
				name = name.replace('.', '/');

				if (!name.endsWith(SUFFIX))
					name = name.concat(SUFFIX);

				// Returns null on lookup failures:
				in = loader.getResourceAsStream(name);
				if (in != null)
				{
					result = new Properties();
					result.load(in); // Can throw IOException
				}
			}
		}
		catch (Exception e)
		{
			result = null;
		}
		finally
		{
			if (in != null)
				try
				{
					in.close();
				}
				catch (Throwable ignore)
				{
				}
		}

		if (THROW_ON_LOAD_FAILURE && (result == null))
		{
			throw new IllegalArgumentException("could not load [" + name + "]" + " as " + (LOAD_AS_RESOURCE_BUNDLE ? "a resource bundle" : "a classloader resource"));
		}

		props = result;
	}

	public String getProperty(String key)
	{
		return props.getProperty(key);
	}
}