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package org.apache.commons.discovery.tools;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
import org.apache.commons.discovery.DiscoveryException;
import org.apache.commons.discovery.Resource;
import org.apache.commons.discovery.listeners.FirstResourceListener;
import org.apache.commons.discovery.resource.ClassLoaders;
import org.apache.commons.discovery.resource.DiscoverResources;
/**
* Mechanisms to locate and load a class.
* The load methods locate a class only.
* The find methods locate a class and verify that the
* class implements an given interface or extends a given class.
*
* @author Richard A. Sitze
* @author Craig R. McClanahan
* @author Costin Manolache
*/
public class ResourceUtils {
/**
* Get package name.
* Not all class loaders 'keep' package information,
* in which case Class.getPackage() returns null.
* This means that calling Class.getPackage().getName()
* is unreliable at best.
*/
public static String getPackageName(Class clazz) {
Package clazzPackage = clazz.getPackage();
String packageName;
if (clazzPackage != null) {
packageName = clazzPackage.getName();
} else {
String clazzName = clazz.getName();
packageName = new String(clazzName.toCharArray(), 0, clazzName.lastIndexOf('.'));
}
return packageName;
}
/**
* Load the resource <code>resourceName</code>.
* Try each classloader in succession,
* until first succeeds, or all fail.
* If all fail and <code>resouceName</code> is not absolute
* (doesn't start with '/' character), then retry with
* <code>packageName/resourceName</code> after changing all
* '.' to '/'.
*
* @param resourceName The name of the resource to load.
*/
public static Resource getResource(Class spi,
String resourceName,
ClassLoaders loaders)
throws DiscoveryException
{
FirstResourceListener listener = new FirstResourceListener();
DiscoverResources explorer = new DiscoverResources(loaders);
explorer.setListener(listener);
explorer.find(resourceName);
if (spi != null &&
(listener.getFirst() == null) &&
resourceName.charAt(0) != '/')
{
/**
* If we didn't find the resource, and if the resourceName
* isn't an 'absolute' path name, then qualify with
* package name of the spi.
*/
explorer.find(getPackageName(spi).replace('.','/') + "/" + resourceName);
}
return listener.getFirst();
}
/**
* Load named property file, optionally qualifed by spi's package name
* as per Class.getResource.
*
* A property file is loaded using the following sequence of class loaders:
* <ul>
* <li>Thread Context Class Loader</li>
* <li>DiscoverSingleton's Caller's Class Loader</li>
* <li>SPI's Class Loader</li>
* <li>DiscoverSingleton's (this class) Class Loader</li>
* <li>System Class Loader</li>
* </ul>
*
* @param
* @param propertiesFileName The property file name.
*
* @return Instance of a class implementing the SPI.
*
* @exception DiscoveryException Thrown if the name of a class implementing
* the SPI cannot be found, if the class cannot be loaded and
* instantiated, or if the resulting class does not implement
* (or extend) the SPI.
*/
public static Properties loadProperties(Class spi,
String propertiesFileName,
ClassLoaders classLoaders)
throws DiscoveryException
{
Properties properties = null;
if (propertiesFileName != null) {
try {
Resource resource = getResource(spi, propertiesFileName, classLoaders);
if (resource != null) {
InputStream stream = resource.getResourceAsStream();
if (stream != null) {
properties = new Properties();
try {
properties.load(stream);
} finally {
stream.close();
}
}
}
} catch (IOException e) {
; // ignore
} catch (SecurityException e) {
; // ignore
}
}
return properties;
}
}