org.terrier.compression
Class BitFileBuffered

java.lang.Object
  org.terrier.compression.BitFileBuffered

All Implemented Interfaces:

java.io.Closeable, BitInSeekable

public class BitFileBuffered
extends java.lang.Object
implements BitInSeekable

Implementation of BitInSeekable/BitIn interfaces similar to BitFile. However this class buffers only a small area of the posting list, to minimise large memory allocations during retrieval. In contrast to BitFile, this class is read-only.

Author:

Patrice Lacour, Craig Macdonald

Nested Class Summary

protected static class

BitFileBuffered.BitInBuffered Implements a BitIn around a RandomDataInput

Field Summary

protected int	buffer_size how much of this file we will buffer
protected static int	DEFAULT_BUFFER_LENGTH how much of a file to buffer by default
protected RandomDataInput	file The underlying file
protected long	fileSize how big the file is, so we know when to stop reading
protected static org.apache.log4j.Logger	logger The logger used

Constructor Summary

BitFileBuffered(java.io.File _file)
Constructs an instance of the class for a given filename, using the default buffer size

BitFileBuffered(java.io.File _file, int bufSize)
Constructs an instance of the class for a given filename

BitFileBuffered(RandomDataInput f)
Constructor for a RandomDataInput object

BitFileBuffered(java.lang.String filename)
Constructs an instance of the class for a given filename.

BitFileBuffered(java.lang.String filename, int bufSize)
Constructs an instance of the class for a given filename

Method Summary

void	close()
BitIn	readReset(long startByteOffset, byte startBitOffset) Reads from the file from a specific offset.
BitIn	readReset(long startByteOffset, byte startBitOffset, long endByteOffset, byte endBitOffset) Reads from the file a specific number of bytes and after this call, a sequence of read calls may follow.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_BUFFER_LENGTH

protected static final int DEFAULT_BUFFER_LENGTH

how much of a file to buffer by default

See Also:

Constant Field Values

logger

protected static final org.apache.log4j.Logger logger

The logger used

file

protected RandomDataInput file

The underlying file

buffer_size

protected final int buffer_size

how much of this file we will buffer

fileSize

protected long fileSize

how big the file is, so we know when to stop reading

Constructor Detail

BitFileBuffered

public BitFileBuffered(RandomDataInput f)

Constructor for a RandomDataInput object

BitFileBuffered

public BitFileBuffered(java.io.File _file)

Constructs an instance of the class for a given filename, using the default buffer size

Parameters:

_file - the underlying file

BitFileBuffered

public BitFileBuffered(java.lang.String filename)

Constructs an instance of the class for a given filename. Default buffer size

Parameters:

filename - java.lang.String the name of the underlying file

BitFileBuffered

public BitFileBuffered(java.io.File _file,
                       int bufSize)

Constructs an instance of the class for a given filename

Parameters:

_file - the underlying file

bufSize - how much of the file to buffer

BitFileBuffered

public BitFileBuffered(java.lang.String filename,
                       int bufSize)

Constructs an instance of the class for a given filename

Parameters:

filename - java.lang.String the name of the underlying file

bufSize - how much of the file to buffer

Method Detail

readReset

public BitIn readReset(long startByteOffset,
                       byte startBitOffset,
                       long endByteOffset,
                       byte endBitOffset)

Reads from the file a specific number of bytes and after this call, a sequence of read calls may follow. The offsets given as arguments are inclusive. For example, if we call this method with arguments 0, 2, 1, 7, it will read in a buffer the contents of the underlying file from the third bit of the first byte to the last bit of the second byte.

Specified by:

readReset in interface BitInSeekable

Parameters:

startByteOffset - the starting byte to read from

startBitOffset - the bit offset in the starting byte

endByteOffset - the ending byte

endBitOffset - the bit offset in the ending byte. This bit is the last bit of this entry.

Returns:

Returns the BitIn object to use to read that data

readReset

public BitIn readReset(long startByteOffset,
                       byte startBitOffset)

Reads from the file from a specific offset. After this call, a sequence of read calls may follow.

Specified by:

readReset in interface BitInSeekable

Parameters:

startByteOffset - the starting byte to read from

startBitOffset - the bit offset in the starting byte

Returns:

Returns the BitIn object to use to read that data

close

public void close()

Specified by:

close in interface java.io.Closeable