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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.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicReference;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.thirdparty.com.google.common.annotations.VisibleForTesting;
/**
* Abstract base class for MapWritable and SortedMapWritable
*
* Unlike org.apache.nutch.crawl.MapWritable, this class allows creation of
* MapWritable<Writable, MapWritable> so the CLASS_TO_ID and ID_TO_CLASS
* maps travel with the class instead of being static.
*
* Class ids range from 1 to 127 so there can be at most 127 distinct classes
* in any specific map instance.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class AbstractMapWritable implements Writable, Configurable {
private AtomicReference conf;
/* Class to id mappings */
@VisibleForTesting
Map, Byte> classToIdMap = new ConcurrentHashMap, Byte>();
/* Id to Class mappings */
@VisibleForTesting
Map> idToClassMap = new ConcurrentHashMap>();
/* The number of new classes (those not established by the constructor) */
private volatile byte newClasses = 0;
/** @return the number of known classes */
byte getNewClasses() {
return newClasses;
}
/**
* Used to add "predefined" classes and by Writable to copy "new" classes.
*/
private synchronized void addToMap(Class clazz, byte id) {
if (classToIdMap.containsKey(clazz)) {
byte b = classToIdMap.get(clazz);
if (b != id) {
throw new IllegalArgumentException ("Class " + clazz.getName() +
" already registered but maps to " + b + " and not " + id);
}
}
if (idToClassMap.containsKey(id)) {
Class c = idToClassMap.get(id);
if (!c.equals(clazz)) {
throw new IllegalArgumentException("Id " + id + " exists but maps to " +
c.getName() + " and not " + clazz.getName());
}
}
classToIdMap.put(clazz, id);
idToClassMap.put(id, clazz);
}
/** Add a Class to the maps if it is not already present. */
protected synchronized void addToMap(Class clazz) {
if (classToIdMap.containsKey(clazz)) {
return;
}
if (newClasses + 1 > Byte.MAX_VALUE) {
throw new IndexOutOfBoundsException("adding an additional class would" +
" exceed the maximum number allowed");
}
byte id = ++newClasses;
addToMap(clazz, id);
}
/** @return the Class class for the specified id */
protected Class getClass(byte id) {
return idToClassMap.get(id);
}
/** @return the id for the specified Class */
protected byte getId(Class clazz) {
return classToIdMap.containsKey(clazz) ? classToIdMap.get(clazz) : -1;
}
/** Used by child copy constructors. */
protected synchronized void copy(Writable other) {
if (other != null) {
try {
DataOutputBuffer out = new DataOutputBuffer();
other.write(out);
DataInputBuffer in = new DataInputBuffer();
in.reset(out.getData(), out.getLength());
readFields(in);
} catch (IOException e) {
throw new IllegalArgumentException("map cannot be copied: " +
e.getMessage());
}
} else {
throw new IllegalArgumentException("source map cannot be null");
}
}
/** constructor. */
protected AbstractMapWritable() {
this.conf = new AtomicReference();
addToMap(ArrayWritable.class, (byte)-127);
addToMap(BooleanWritable.class, (byte)-126);
addToMap(BytesWritable.class, (byte)-125);
addToMap(FloatWritable.class, (byte)-124);
addToMap(IntWritable.class, (byte)-123);
addToMap(LongWritable.class, (byte)-122);
addToMap(MapWritable.class, (byte)-121);
addToMap(MD5Hash.class, (byte)-120);
addToMap(NullWritable.class, (byte)-119);
addToMap(ObjectWritable.class, (byte)-118);
addToMap(SortedMapWritable.class, (byte)-117);
addToMap(Text.class, (byte)-116);
addToMap(TwoDArrayWritable.class, (byte)-115);
// UTF8 is deprecated so we don't support it
addToMap(VIntWritable.class, (byte)-114);
addToMap(VLongWritable.class, (byte)-113);
}
/** @return the conf */
@Override
public Configuration getConf() {
return conf.get();
}
/** @param conf the conf to set */
@Override
public void setConf(Configuration conf) {
this.conf.set(conf);
}
@Override
public void write(DataOutput out) throws IOException {
// First write out the size of the class table and any classes that are
// "unknown" classes
out.writeByte(newClasses);
for (byte i = 1; i <= newClasses; i++) {
out.writeByte(i);
out.writeUTF(getClass(i).getName());
}
}
@Override
public void readFields(DataInput in) throws IOException {
// Get the number of "unknown" classes
newClasses = in.readByte();
// Use the classloader of the current thread to load classes instead of the
// system-classloader so as to support both client-only and inside-a-MR-job
// use-cases. The context-loader by default eventually falls back to the
// system one, so there should be no cases where changing this is an issue.
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// Then read in the class names and add them to our tables
for (int i = 0; i < newClasses; i++) {
byte id = in.readByte();
String className = in.readUTF();
try {
addToMap(classLoader.loadClass(className), id);
} catch (ClassNotFoundException e) {
throw new IOException(e);
}
}
}
}
