org.apache.hadoop.hbase.CompatibilitySingletonFactory 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.hadoop.hbase;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.ServiceLoader;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* Factory for classes supplied by hadoop compatibility modules. Only one of each class will be
* created.
*/
@InterfaceAudience.Private
public class CompatibilitySingletonFactory extends CompatibilityFactory {
public static enum SingletonStorage {
INSTANCE;
private final Object lock = new Object();
private final Map instances = new HashMap<>();
}
private static final Logger LOG = LoggerFactory.getLogger(CompatibilitySingletonFactory.class);
/**
* This is a static only class don't let anyone create an instance.
*/
protected CompatibilitySingletonFactory() { }
/**
* Get the singleton instance of Any classes defined by compatibiliy jar's
*
* @return the singleton
*/
@SuppressWarnings("unchecked")
public static T getInstance(Class klass) {
synchronized (SingletonStorage.INSTANCE.lock) {
T instance = (T) SingletonStorage.INSTANCE.instances.get(klass);
if (instance == null) {
try {
ServiceLoader loader = ServiceLoader.load(klass);
Iterator it = loader.iterator();
instance = it.next();
if (it.hasNext()) {
StringBuilder msg = new StringBuilder();
msg.append("ServiceLoader provided more than one implementation for class: ")
.append(klass)
.append(", using implementation: ").append(instance.getClass())
.append(", other implementations: {");
while (it.hasNext()) {
msg.append(it.next()).append(" ");
}
msg.append("}");
LOG.warn(msg.toString());
}
} catch (Exception e) {
throw new RuntimeException(createExceptionString(klass), e);
} catch (Error e) {
throw new RuntimeException(createExceptionString(klass), e);
}
// If there was nothing returned and no exception then throw an exception.
if (instance == null) {
throw new RuntimeException(createExceptionString(klass));
}
SingletonStorage.INSTANCE.instances.put(klass, instance);
}
return instance;
}
}
}