VersionedWritable.java
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上传日期:2018-01-08
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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.DataOutput;
- import java.io.DataInput;
- import java.io.IOException;
- /** 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}.
- */
- public abstract class VersionedWritable implements Writable {
- /** Return the version number of the current implementation. */
- public abstract byte getVersion();
-
- // javadoc from Writable
- public void write(DataOutput out) throws IOException {
- out.writeByte(getVersion()); // store version
- }
- // javadoc from Writable
- public void readFields(DataInput in) throws IOException {
- byte version = in.readByte(); // read version
- if (version != getVersion())
- throw new VersionMismatchException(getVersion(), version);
- }
-
- }