org.apache.brooklyn.api.internal.ApiObjectsFactory Maven / Gradle / Ivy
/*
* 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.brooklyn.api.internal;
import org.apache.brooklyn.api.framework.FrameworkLookup;
import org.apache.brooklyn.util.guava.Maybe;
import com.google.common.annotations.Beta;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* This class grants access to implementations in core for operations needed in API classes.
* The majority of the API classes are interfaces or have minimal behaviour, but there are a
* few instances where more complex behaviour from core is desired.
*
* This class acts as a bridge for those instances. See the concrete implementation of the
* {@link ApiObjectsFactoryInterface} in brooklyn-core class ApiObjectsFactoryImpl.
*/
@Beta
public class ApiObjectsFactory {
private static final Logger LOG = LoggerFactory.getLogger(ApiObjectsFactory.class);
private static Maybe INSTANCE;
private static synchronized ApiObjectsFactoryInterface getFactoryInstance() {
// defer initialization to allow any other static initialization to complete,
// and use maybe so we (1) don't check multiple times, but (2) do throw error in the caller's stack
if (INSTANCE!=null) return INSTANCE.get();
INSTANCE = Maybe.absent("Implementation of " + ApiObjectsFactoryInterface.class + " not found.");
final Maybe factory = FrameworkLookup.lookup(ApiObjectsFactoryInterface.class);
if (factory.isPresent()) {
INSTANCE = factory;
}
return INSTANCE.get();
}
/**
* Create (if necessary) and return the concrete implementation from core for the
* methods exposed here. */
public static ApiObjectsFactoryInterface get() {
return getFactoryInstance();
}
}