/**
* Copyright 2010 JBoss Inc
*
* 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.
*/
/*
* 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.
*/
package org.drools.util;
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;
}
}