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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.util.Enumeration;
import java.util.NoSuchElementException;
import org.apache.commons.discovery.ResourceClass;
import org.apache.commons.discovery.ResourceClassIterator;
import org.apache.commons.discovery.ResourceNameIterator;
import org.apache.commons.discovery.resource.ClassLoaders;
import org.apache.commons.discovery.resource.classes.DiscoverClasses;
import org.apache.commons.discovery.resource.names.DiscoverServiceNames;
/**
* [this was ServiceDiscovery12... the 1.1 versus 1.2 issue
* has been abstracted to org.apache.commons.discover.jdk.JDKHooks]
*
* Implement the JDK1.3 'Service Provider' specification.
* ( http://java.sun.com/j2se/1.3/docs/guide/jar/jar.html )
*
*
* This class supports any VM, including JDK1.1, via
* org.apache.commons.discover.jdk.JDKHooks.
*
* The caller will first configure the discoverer by adding ( in the desired
* order ) all the places to look for the META-INF/services. Currently
* we support loaders.
*
* The findResources() method will check every loader.
*/
public class Service {
/**
* Construct a new service discoverer
*/
protected Service() {
}
/**
* as described in
* sun/jdk1.3.1/docs/guide/jar/jar.html#Service Provider,
* Except this uses Enumeration
* instead of Interator.
*
* @param Service Provider Interface type
* @param Any type extends the SPI type
* @param spiClass Service Provider Interface Class
* @return Enumeration of class instances ({@code S})
*/
public static Enumeration providers(Class spiClass) {
return providers(new SPInterface(spiClass), null);
}
/**
* This version lets you specify constructor arguments..
*
* @param Service Provider Interface type
* @param Any type extends the SPI type
* @param spi SPI to look for and load.
* @param loaders loaders to use in search.
* If null then use ClassLoaders.getAppLoaders().
* @return Enumeration of class instances ({@code S})
*/
public static Enumeration providers(final SPInterface spi,
ClassLoaders loaders) {
if (loaders == null) {
loaders = ClassLoaders.getAppLoaders(spi.getSPClass(),
Service.class,
true);
}
ResourceNameIterator servicesIter =
(new DiscoverServiceNames(loaders)).findResourceNames(spi.getSPName());
final ResourceClassIterator services =
(new DiscoverClasses(loaders)).findResourceClasses(servicesIter);
return new Enumeration() {
private S object = getNextClassInstance();
public boolean hasMoreElements() {
return object != null;
}
public S nextElement() {
if (object == null) {
throw new NoSuchElementException();
}
S obj = object;
object = getNextClassInstance();
return obj;
}
private S getNextClassInstance() {
while (services.hasNext()) {
ResourceClass info = services.nextResourceClass();
try {
return spi.newInstance(info.loadClass());
} catch (Exception e) {
// ignore
} catch (LinkageError le) {
// ignore
}
}
return null;
}
};
}
}