org.apache.hadoop.io.WritableName 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.io;
import java.util.HashMap;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
/** Utility to permit renaming of Writable implementation classes without
* invalidiating files that contain their class name.
*/
public class WritableName {
private static HashMap> NAME_TO_CLASS =
new HashMap>();
private static HashMap, String> CLASS_TO_NAME =
new HashMap, 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;
}
}
}