hadoop MapWritable 源码
haddop MapWritable 代码
文件路径:/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/MapWritable.java
/**
* 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.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.util.ReflectionUtils;
/**
* A Writable Map.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class MapWritable extends AbstractMapWritable
implements Map<Writable, Writable> {
private Map<Writable, Writable> instance;
/** Default constructor. */
public MapWritable() {
super();
this.instance = new HashMap<Writable, Writable>();
}
/**
* Copy constructor.
*
* @param other the map to copy from
*/
public MapWritable(MapWritable other) {
this();
copy(other);
}
@Override
public void clear() {
instance.clear();
}
@Override
public boolean containsKey(Object key) {
return instance.containsKey(key);
}
@Override
public boolean containsValue(Object value) {
return instance.containsValue(value);
}
@Override
public Set<Map.Entry<Writable, Writable>> entrySet() {
return instance.entrySet();
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj instanceof MapWritable) {
MapWritable map = (MapWritable) obj;
if (size() != map.size()) {
return false;
}
return entrySet().equals(map.entrySet());
}
return false;
}
@Override
public Writable get(Object key) {
return instance.get(key);
}
@Override
public int hashCode() {
return 1 + this.instance.hashCode();
}
@Override
public boolean isEmpty() {
return instance.isEmpty();
}
@Override
public Set<Writable> keySet() {
return instance.keySet();
}
@Override
public Writable put(Writable key, Writable value) {
addToMap(key.getClass());
addToMap(value.getClass());
return instance.put(key, value);
}
@Override
public void putAll(Map<? extends Writable, ? extends Writable> t) {
for (Map.Entry<? extends Writable, ? extends Writable> e: t.entrySet()) {
put(e.getKey(), e.getValue());
}
}
@Override
public Writable remove(Object key) {
return instance.remove(key);
}
@Override
public int size() {
return instance.size();
}
@Override
public Collection<Writable> values() {
return instance.values();
}
// Writable
@Override
public void write(DataOutput out) throws IOException {
super.write(out);
// Write out the number of entries in the map
out.writeInt(instance.size());
// Then write out each key/value pair
for (Map.Entry<Writable, Writable> e: instance.entrySet()) {
out.writeByte(getId(e.getKey().getClass()));
e.getKey().write(out);
out.writeByte(getId(e.getValue().getClass()));
e.getValue().write(out);
}
}
@Override
public void readFields(DataInput in) throws IOException {
super.readFields(in);
// First clear the map. Otherwise we will just accumulate
// entries every time this method is called.
this.instance.clear();
// Read the number of entries in the map
int entries = in.readInt();
// Then read each key/value pair
for (int i = 0; i < entries; i++) {
Writable key = (Writable) ReflectionUtils.newInstance(getClass(
in.readByte()), getConf());
key.readFields(in);
Writable value = (Writable) ReflectionUtils.newInstance(getClass(
in.readByte()), getConf());
value.readFields(in);
instance.put(key, value);
}
}
@Override
public String toString() {
return instance.toString();
}
}
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