| /** |
| * 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; |
| } |
| } |
| |
| } |