[120] | 1 | /** |
---|
| 2 | * Licensed to the Apache Software Foundation (ASF) under one |
---|
| 3 | * or more contributor license agreements. See the NOTICE file |
---|
| 4 | * distributed with this work for additional information |
---|
| 5 | * regarding copyright ownership. The ASF licenses this file |
---|
| 6 | * to you under the Apache License, Version 2.0 (the |
---|
| 7 | * "License"); you may not use this file except in compliance |
---|
| 8 | * with the License. You may obtain a copy of the License at |
---|
| 9 | * |
---|
| 10 | * http://www.apache.org/licenses/LICENSE-2.0 |
---|
| 11 | * |
---|
| 12 | * Unless required by applicable law or agreed to in writing, software |
---|
| 13 | * distributed under the License is distributed on an "AS IS" BASIS, |
---|
| 14 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
---|
| 15 | * See the License for the specific language governing permissions and |
---|
| 16 | * limitations under the License. |
---|
| 17 | */ |
---|
| 18 | |
---|
| 19 | package org.apache.hadoop.io; |
---|
| 20 | |
---|
| 21 | import java.util.HashMap; |
---|
| 22 | import java.io.IOException; |
---|
| 23 | |
---|
| 24 | import org.apache.hadoop.conf.Configuration; |
---|
| 25 | |
---|
| 26 | /** Utility to permit renaming of Writable implementation classes without |
---|
| 27 | * invalidiating files that contain their class name. |
---|
| 28 | */ |
---|
| 29 | public class WritableName { |
---|
| 30 | private static HashMap<String, Class<?>> NAME_TO_CLASS = |
---|
| 31 | new HashMap<String, Class<?>>(); |
---|
| 32 | private static HashMap<Class<?>, String> CLASS_TO_NAME = |
---|
| 33 | new HashMap<Class<?>, String>(); |
---|
| 34 | |
---|
| 35 | static { // define important types |
---|
| 36 | WritableName.setName(NullWritable.class, "null"); |
---|
| 37 | WritableName.setName(LongWritable.class, "long"); |
---|
| 38 | WritableName.setName(UTF8.class, "UTF8"); |
---|
| 39 | WritableName.setName(MD5Hash.class, "MD5Hash"); |
---|
| 40 | } |
---|
| 41 | |
---|
| 42 | private WritableName() {} // no public ctor |
---|
| 43 | |
---|
| 44 | /** Set the name that a class should be known as to something other than the |
---|
| 45 | * class name. */ |
---|
| 46 | public static synchronized void setName(Class writableClass, String name) { |
---|
| 47 | CLASS_TO_NAME.put(writableClass, name); |
---|
| 48 | NAME_TO_CLASS.put(name, writableClass); |
---|
| 49 | } |
---|
| 50 | |
---|
| 51 | /** Add an alternate name for a class. */ |
---|
| 52 | public static synchronized void addName(Class writableClass, String name) { |
---|
| 53 | NAME_TO_CLASS.put(name, writableClass); |
---|
| 54 | } |
---|
| 55 | |
---|
| 56 | /** Return the name for a class. Default is {@link Class#getName()}. */ |
---|
| 57 | public static synchronized String getName(Class writableClass) { |
---|
| 58 | String name = CLASS_TO_NAME.get(writableClass); |
---|
| 59 | if (name != null) |
---|
| 60 | return name; |
---|
| 61 | return writableClass.getName(); |
---|
| 62 | } |
---|
| 63 | |
---|
| 64 | /** Return the class for a name. Default is {@link Class#forName(String)}.*/ |
---|
| 65 | public static synchronized Class<?> getClass(String name, Configuration conf |
---|
| 66 | ) throws IOException { |
---|
| 67 | Class<?> writableClass = NAME_TO_CLASS.get(name); |
---|
| 68 | if (writableClass != null) |
---|
| 69 | return writableClass.asSubclass(Writable.class); |
---|
| 70 | try { |
---|
| 71 | return conf.getClassByName(name); |
---|
| 72 | } catch (ClassNotFoundException e) { |
---|
| 73 | IOException newE = new IOException("WritableName can't load class: " + name); |
---|
| 74 | newE.initCause(e); |
---|
| 75 | throw newE; |
---|
| 76 | } |
---|
| 77 | } |
---|
| 78 | |
---|
| 79 | } |
---|