Maintains a mapping of service names to an ordered set of service providers when running in an OSGi container.
/*
* 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.
*/
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Callable;
/**
* Maintains a mapping of service names to an ordered set of service providers
* when running in an OSGi container. <p/> It is expected that a bundle using
* Drools will populate this map with properties from its own ClassLoader. <p/>
* This is an adaptation of the technique described by Guillaume Nodet in his
* article<i> <a
* href='http://gnodet.blogspot.com/2008/05/jee-specs-in-osgi.html'> Java EE
* specs in OSGi</a></i>. The main changes were to add comments.
*
* @author Guillaume Nodet
* @author Faron Dutton
* @see {@linkplain http://gnodet.blogspot.com/2008/05/jee-specs-in-osgi.html}
*/
public final class OSGiLocator {
/**
* Maps a service name (the fully qualified name of the interface) to an
* ordered set of factories. Each factory instantiating a specific service
* provider (implementation).
*/
private static Map<String, List<Callable<Class<?>>>> factories;
/**
* Private constructor used to prevent instantiation of this utility class
* (i.e., Utility Pattern).
*/
private OSGiLocator() {
super();
}
/**
* Removes the given service provider factory from the set of providers for
* the service.
*
* @param serviceName
* The fully qualified name of the service interface.
* @param factory
* A factory for creating a specific type of service provider. May be
* <tt>null</tt> in which case this method does nothing.
* @throws IllegalArgumentException
* if serviceName is <tt>null</tt>
*/
public static synchronized void unregister(final String serviceName,
final Callable<Class<?>> factory) {
if (serviceName == null) {
throw new IllegalArgumentException("serviceName cannot be null");
}
if (factories != null) {
List<Callable<Class<?>>> l = factories.get(serviceName);
if (l != null) {
l.remove(factory);
}
}
}
/**
* Adds the given service provider factory to the set of providers for the
* service.
*
* @param serviceName
* The fully qualified name of the service interface.
* @param factory
* A factory for creating a specific type of service provider. May be
* <tt>null</tt> in which case this method does nothing.
* @throws IllegalArgumentException
* if serviceName is <tt>null</tt>
*/
public static synchronized void register(final String serviceName,
final Callable<Class<?>> factory) {
if (serviceName == null) {
throw new IllegalArgumentException("serviceName cannot be null");
}
if (factory != null) {
if (factories == null) {
factories = new HashMap<String, List<Callable<Class<?>>>>();
}
List<Callable<Class<?>>> l = factories.get(serviceName);
if (l == null) {
l = new ArrayList<Callable<Class<?>>>();
factories.put(serviceName, l);
}
l.add(factory);
}
}
/**
* Finds the preferred provider for the given service. The preferred provider
* is the last one added to the set of providers.
*
* @param serviceName
* The fully qualified name of the service interface.
* @return The last provider added for the service if any exists. Otherwise,
* it returns <tt>null</tt>.
* @throws IllegalArgumentException
* if serviceName is <tt>null</tt>
*/
public static synchronized Class<?> locate(final String serviceName) {
if (serviceName == null) {
throw new IllegalArgumentException("serviceName cannot be null");
}
if (factories != null) {
List<Callable<Class<?>>> l = factories.get(serviceName);
if (l != null && !l.isEmpty()) {
Callable<Class<?>> c = l.get(l.size() - 1);
try {
return c.call();
} catch (Exception e) {
}
}
}
return null;
}
/**
* Finds all providers for the given service.
*
* @param serviceName
* The fully qualified name of the service interface.
* @return The ordered set of providers for the service if any exists.
* Otherwise, it returns an empty list.
* @throws IllegalArgumentException
* if serviceName is <tt>null</tt>
*/
public static synchronized List<Class<?>> locateAll(final String serviceName) {
if (serviceName == null) {
throw new IllegalArgumentException("serviceName cannot be null");
}
List<Class<?>> classes = new ArrayList<Class<?>>();
if (factories != null) {
List<Callable<Class<?>>> l = factories.get(serviceName);
if (l != null) {
for (Callable<Class<?>> c : l) {
try {
classes.add(c.call());
} catch (Exception e) {
}
}
}
}
return classes;
}
}
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