hadoop WritableFactories 源码
haddop WritableFactories 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/WritableFactories.java
/**
* 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.io;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.util.ReflectionUtils;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
/** Factories for non-public writables. Defining a factory permits {@link
* ObjectWritable} to be able to construct instances of non-public classes. */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class WritableFactories {
private static final Map<Class, WritableFactory> CLASS_TO_FACTORY =
new ConcurrentHashMap<Class, WritableFactory>();
private WritableFactories() {} // singleton
/**
* Define a factory for a class.
* @param c input c.
* @param factory input factory.
*/
public static void setFactory(Class c, WritableFactory factory) {
CLASS_TO_FACTORY.put(c, factory);
}
/**
* Define a factory for a class.
* @param c input c.
* @return a factory for a class.
*/
public static WritableFactory getFactory(Class c) {
return CLASS_TO_FACTORY.get(c);
}
/**
* Create a new instance of a class with a defined factory.
*
* @param c input c.
* @param conf input configuration.
* @return a new instance of a class with a defined factory.
*/
public static Writable newInstance(Class<? extends Writable> c, Configuration conf) {
WritableFactory factory = WritableFactories.getFactory(c);
if (factory != null) {
Writable result = factory.newInstance();
if (result instanceof Configurable) {
((Configurable) result).setConf(conf);
}
return result;
} else {
return ReflectionUtils.newInstance(c, conf);
}
}
/**
* Create a new instance of a class with a defined factory.
* @param c input c.
* @return a new instance of a class with a defined factory.
*/
public static Writable newInstance(Class<? extends Writable> c) {
return newInstance(c, null);
}
}
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