001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.io;
020
021import org.apache.hadoop.classification.InterfaceAudience;
022import org.apache.hadoop.classification.InterfaceStability;
023import org.apache.hadoop.conf.*;
024import org.apache.hadoop.util.ReflectionUtils;
025import java.util.Map;
026import java.util.concurrent.ConcurrentHashMap;
027
028/** Factories for non-public writables.  Defining a factory permits {@link
029 * ObjectWritable} to be able to construct instances of non-public classes. */
030@InterfaceAudience.Public
031@InterfaceStability.Stable
032public class WritableFactories {
033  private static final Map<Class, WritableFactory> CLASS_TO_FACTORY =
034    new ConcurrentHashMap<Class, WritableFactory>();
035
036  private WritableFactories() {}                  // singleton
037
038  /** Define a factory for a class. */
039  public static void setFactory(Class c, WritableFactory factory) {
040    CLASS_TO_FACTORY.put(c, factory);
041  }
042
043  /** Define a factory for a class. */
044  public static WritableFactory getFactory(Class c) {
045    return CLASS_TO_FACTORY.get(c);
046  }
047
048  /** Create a new instance of a class with a defined factory. */
049  public static Writable newInstance(Class<? extends Writable> c, Configuration conf) {
050    WritableFactory factory = WritableFactories.getFactory(c);
051    if (factory != null) {
052      Writable result = factory.newInstance();
053      if (result instanceof Configurable) {
054        ((Configurable) result).setConf(conf);
055      }
056      return result;
057    } else {
058      return ReflectionUtils.newInstance(c, conf);
059    }
060  }
061  
062  /** Create a new instance of a class with a defined factory. */
063  public static Writable newInstance(Class<? extends Writable> c) {
064    return newInstance(c, null);
065  }
066
067}
068