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Its an port to fix bugs in OSGi support. ... The Apache Commons Discovery 0.5 component is about discovering, or finding,
implementations for pluggable interfaces.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.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.ResourceIterator;
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.
*/
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.
*
* @param clazz The class from which the package has to be extracted
* @return The string representation of the input class package
*/
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 resourceName.
*
* Try each classloader in succession,
* until first succeeds, or all fail.
* If all fail and resouceName is not absolute
* (doesn't start with '/' character), then retry with
* packageName/resourceName after changing all
* '.' to '/'.
*
* @param spi The SPI type
* @param resourceName The name of the resource to load.
* @param loaders the class loaders holder
* @return The discovered {@link Resource} instance
* @throws DiscoveryException if the class implementing
* the SPI cannot be found, cannot be loaded and
* instantiated, or if the resulting class does not implement
* (or extend) the SPI
*/
public static Resource getResource(Class spi,
String resourceName,
ClassLoaders loaders) throws DiscoveryException {
DiscoverResources explorer = new DiscoverResources(loaders);
ResourceIterator resources = explorer.findResources(resourceName);
if (spi != null &&
!resources.hasNext() &&
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.
*/
resourceName = getPackageName(spi).replace('.','/') + "/" + resourceName;
resources = explorer.findResources(resourceName);
}
return resources.hasNext()
? resources.nextResource()
: null;
}
/**
* Load named property file, optionally qualified by spi's package name
* as per Class.getResource.
*
* A property file is loaded using the following sequence of class loaders:
*
* - Thread Context Class Loader
* - DiscoverSingleton's Caller's Class Loader
* - SPI's Class Loader
* - DiscoverSingleton's (this class) Class Loader
* - System Class Loader
*
*
* @param spi The SPI type
* @param propertiesFileName The property file name.
* @param classLoaders The class loaders holder
* @return The loaded named property file, in {@code Properties} format
* @throws 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;
}
}