Package nom.tam.fits.compress

Class CompressionManager

java.lang.Object

nom.tam.fits.compress.CompressionManager

public final class CompressionManager
extends Object

(for internal use) Decompression of compressed FITS files of all supported types (.gz, .Z, .bz2). It autodetects the type of compression used based on the first 2-bytes of the compressed input stream. When possible, preference will be given to perform the decompression using a system command (uncompress or bzip2, which are likely faster for large files). If such a tool is not available, then the Apache common-compress classes will be used to the same effect.

See Also:

• GZipCompressionProvider
• BZip2CompressionProvider
• ZCompressionProvider

Field Summary

Fields

Modifier and Type	Field	Description
static final int	ONE_MEGABYTE	bytes in a megabyte (MB)

Method Summary

Modifier and Type	Method	Description
static InputStream	decompress(InputStream compressed)	This method decompresses a compressed input stream.
static boolean	isCompressed(File file)	Is a file compressed? (the magic number in the first 2 bytes is used to detect the compression.
static boolean	isCompressed(String filename)	Checks if a file is compressed.
protected static ICompressProvider	nextCompressionProvider(int mag1, int mag2, ICompressProvider old)	Returned the next highest priority decompression class, after the one we don't want, for the given type of compressed file.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

ONE_MEGABYTE

public static final int ONE_MEGABYTE

bytes in a megabyte (MB)

See Also:

• Constant Field Values

Method Details

decompress

public static InputStream decompress(InputStream compressed)
                              throws FitsException

This method decompresses a compressed input stream. The decompression method is selected automatically based upon the first two bytes read.

Parameters:

compressed - The compressed input stream

Returns:

A stream which wraps the input stream and decompresses it. If the input stream is not compressed, a pushback input stream wrapping the original stream is returned.

Throws:

FitsException - when the stream could not be read or decompressed

isCompressed

public static boolean isCompressed(File file)

Is a file compressed? (the magic number in the first 2 bytes is used to detect the compression.

Parameters:

file - file to test for compression algorithms

Returns:

true if the file is compressed

isCompressed

public static boolean isCompressed(String filename)

Checks if a file is compressed. If the file by the name exists, it will check the magic number in the first 2-bytes to see if they matched those of the supported compression algorithms. Otherwise it checks if the file extension atches one of the standard extensions for supported compressed files (.gz, .Z, or .bz2).

As of 1.18, all file extension are checked in a case insensitive manner

Parameters:

filename - of the file to test for compression algorithms

Returns:

true if the file is compressed

nextCompressionProvider

protected static ICompressProvider nextCompressionProvider(int mag1,
 int mag2,
 ICompressProvider old)

Returned the next highest priority decompression class, after the one we don't want, for the given type of compressed file.

Parameters:

mag1 - the first magic byte at the head of the compressed file

mag2 - the second magic byte at the head of the compressed file

old - the last decompression class we tried for this type of file

Returns:

the next lower priority decompression class we might use.