org.apache.hadoop.io.compress.SplittableCompressionCodec Maven / Gradle / Ivy
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* 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,
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* See the License for the specific language governing permissions and
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*/
package org.apache.hadoop.io.compress;
import java.io.IOException;
import java.io.InputStream;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* This interface is meant to be implemented by those compression codecs
* which are capable to compress / de-compress a stream starting at any
* arbitrary position.
*
* Especially the process of de-compressing a stream starting at some arbitrary
* position is challenging. Most of the codecs are only able to successfully
* de-compress a stream, if they start from the very beginning till the end.
* One of the reasons is the stored state at the beginning of the stream which
* is crucial for de-compression.
*
* Yet there are few codecs which do not save the whole state at the beginning
* of the stream and hence can be used to de-compress stream starting at any
* arbitrary points. This interface is meant to be used by such codecs. Such
* codecs are highly valuable, especially in the context of Hadoop, because
* an input compressed file can be split and hence can be worked on by multiple
* machines in parallel.
*/
@InterfaceAudience.Public
@InterfaceStability.Evolving
public interface SplittableCompressionCodec extends CompressionCodec {
/**
* During decompression, data can be read off from the decompressor in two
* modes, namely continuous and blocked. Few codecs (e.g. BZip2) are capable
* of compressing data in blocks and then decompressing the blocks. In
* Blocked reading mode codecs inform 'end of block' events to its caller.
* While in continuous mode, the caller of codecs is unaware about the blocks
* and uncompressed data is spilled out like a continuous stream.
*/
public enum READ_MODE {CONTINUOUS, BYBLOCK};
/**
* Create a stream as dictated by the readMode. This method is used when
* the codecs wants the ability to work with the underlying stream positions.
*
* @param seekableIn The seekable input stream (seeks in compressed data)
* @param start The start offset into the compressed stream. May be changed
* by the underlying codec.
* @param end The end offset into the compressed stream. May be changed by
* the underlying codec.
* @param readMode Controls whether stream position is reported continuously
* from the compressed stream only only at block boundaries.
* @return a stream to read uncompressed bytes from
*/
SplitCompressionInputStream createInputStream(InputStream seekableIn,
Decompressor decompressor, long start, long end, READ_MODE readMode)
throws IOException;
}