Database Reference
In-Depth Information
Compressing and decompressing streams with CompressionCodec
CompressionCodec
has two methods that allow you to easily compress or decompress
data. To compress data being written to an output stream, use the
createOut-
putStream(OutputStream out)
method to create a
CompressionOut-
putStream
to which you write your uncompressed data to have it written in compressed
form to the underlying stream. Conversely, to decompress data being read from an input
stream, call
createInputStream(InputStream in)
to obtain a
Compres-
sionInputStream
, which allows you to read uncompressed data from the underlying
stream.
CompressionOutputStream
and
CompressionInputStream
are similar to
java.util.zip.DeflaterOutputStream
and
java.util.zip.DeflaterInputStream
, except that both of the former provide
the ability to reset their underlying compressor or decompressor. This is important for ap-
plications that compress sections of the data stream as separate blocks, such as in a
SequenceFile
, described in
SequenceFile
.
Example 5-1
illustrates how to use the API to compress data read from standard input and
write it to standard output.
Example 5-1. A program to compress data read from standard input and write it to stand-
ard output
public class
StreamCompressor
{
public static
void
main
(
String
[]
args
)
throws
Exception
{
String codecClassname
=
args
[
0
];
Class
<?>
codecClass
=
Class
.
forName
(
codecClassname
);
Configuration conf
=
new
Configuration
();
CompressionCodec codec
= (
CompressionCodec
)
ReflectionUtils
.
newInstance
(
codecClass
,
conf
);
CompressionOutputStream out
=
codec
.
createOutputStream
(
System
.
out
);
IOUtils
.
copyBytes
(
System
.
in
,
out
,
4096
,
false
);
out
.
finish
();
}
}
The application expects the fully qualified name of the
CompressionCodec
imple-
mentation as the first command-line argument. We use
ReflectionUtils
to construct
a new instance of the codec, then obtain a compression wrapper around
System.out
.
Then we call the utility method
copyBytes()
on
IOUtils
to copy the input to the
