org.apache.hadoop.io.WritableName.java Source code

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Here is the source code for org.apache.hadoop.io.WritableName.java

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/**
 * 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 java.util.HashMap;
import java.io.IOException;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;

/** Utility to permit renaming of Writable implementation classes without
 * invalidiating files that contain their class name.
 */
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class WritableName {
    private static HashMap<String, Class<?>> NAME_TO_CLASS = new HashMap<String, Class<?>>();
    private static HashMap<Class<?>, String> CLASS_TO_NAME = new HashMap<Class<?>, String>();

    static { // define important types
        WritableName.setName(NullWritable.class, "null");
        WritableName.setName(LongWritable.class, "long");
        WritableName.setName(UTF8.class, "UTF8");
        WritableName.setName(MD5Hash.class, "MD5Hash");
    }

    private WritableName() {
    } // no public ctor

    /** Set the name that a class should be known as to something other than the
     * class name. */
    public static synchronized void setName(Class<?> writableClass, String name) {
        CLASS_TO_NAME.put(writableClass, name);
        NAME_TO_CLASS.put(name, writableClass);
    }

    /** Add an alternate name for a class. */
    public static synchronized void addName(Class<?> writableClass, String name) {
        NAME_TO_CLASS.put(name, writableClass);
    }

    /** Return the name for a class.  Default is {@link Class#getName()}. */
    public static synchronized String getName(Class<?> writableClass) {
        String name = CLASS_TO_NAME.get(writableClass);
        if (name != null)
            return name;
        return writableClass.getName();
    }

    /** Return the class for a name.  Default is {@link Class#forName(String)}.*/
    public static synchronized Class<?> getClass(String name, Configuration conf) throws IOException {
        Class<?> writableClass = NAME_TO_CLASS.get(name);
        if (writableClass != null)
            return writableClass.asSubclass(Writable.class);
        try {
            return conf.getClassByName(name);
        } catch (ClassNotFoundException e) {
            IOException newE = new IOException("WritableName can't load class: " + name);
            newE.initCause(e);
            throw newE;
        }
    }

}