hadoop VersionedWritable 源码
haddop VersionedWritable 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/VersionedWritable.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.DataOutput;
import java.io.DataInput;
import java.io.IOException;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/** A base class for Writables that provides version checking.
*
* <p>This is useful when a class may evolve, so that instances written by the
* old version of the class may still be processed by the new version. To
* handle this situation, {@link #readFields(DataInput)}
* implementations should catch {@link VersionMismatchException}.
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class VersionedWritable implements Writable {
/** @return Return the version number of the current implementation. */
public abstract byte getVersion();
// javadoc from Writable
@Override
public void write(DataOutput out) throws IOException {
out.writeByte(getVersion()); // store version
}
// javadoc from Writable
@Override
public void readFields(DataInput in) throws IOException {
byte version = in.readByte(); // read version
if (version != getVersion())
throw new VersionMismatchException(getVersion(), version);
}
}
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