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.HashMap;
026
027/** Factories for non-public writables.  Defining a factory permits {@link
028 * ObjectWritable} to be able to construct instances of non-public classes. */
029@InterfaceAudience.Public
030@InterfaceStability.Stable
031public class WritableFactories {
032  private static final HashMap<Class, WritableFactory> CLASS_TO_FACTORY =
033    new HashMap<Class, WritableFactory>();
034
035  private WritableFactories() {}                  // singleton
036
037  /** Define a factory for a class. */
038  public static synchronized void setFactory(Class c, WritableFactory factory) {
039    CLASS_TO_FACTORY.put(c, factory);
040  }
041
042  /** Define a factory for a class. */
043  public static synchronized WritableFactory getFactory(Class c) {
044    return CLASS_TO_FACTORY.get(c);
045  }
046
047  /** Create a new instance of a class with a defined factory. */
048  public static Writable newInstance(Class<? extends Writable> c, Configuration conf) {
049    WritableFactory factory = WritableFactories.getFactory(c);
050    if (factory != null) {
051      Writable result = factory.newInstance();
052      if (result instanceof Configurable) {
053        ((Configurable) result).setConf(conf);
054      }
055      return result;
056    } else {
057      return ReflectionUtils.newInstance(c, conf);
058    }
059  }
060  
061  /** Create a new instance of a class with a defined factory. */
062  public static Writable newInstance(Class<? extends Writable> c) {
063    return newInstance(c, null);
064  }
065
066}
067