AsciiDatabase
Class AsciiReader

java.lang.Object
  |
  +--AsciiDatabase.AsciiReader

public final class AsciiReader

extends Object

A fully buffered, random access reader capable of reading both fixed sized blocks and carrage return terminated lines. Also, can read from either normal uncompressed files, or GZIP compressed files.

Author:

chris.studholme@utoronto.ca

Field Summary

private byte[]	buffer Buffer used to improve performance of small reads.
static int	buffersize Default buffer size for uncompressed files.
private File	file Open file.
private RandomAccessFile	stream Stream used for uncompressed file.
private long	streampos Current stream position.
private int	validlength Length of valid data in buffer.
private int	validoffset Offset of next valid data in buffer.
private GZIPInputStream	zstream Stream used for compressed file.
static int	zstreambuffer Default buffer size for compressed files.

Constructor Summary

AsciiReader(String filename)
Open an uncompressed file by name.

AsciiReader(String filename, boolean gzip)
Open an uncompressed or compressed file by name.

Method Summary

void	close() Close the data file.
protected void	finalize() Close the data file.
long	getFilePointer() Return the current file pointer position.
long	length() Return the length of the file.
void	pushBack() Push back the last byte read so it can be read again.
int	read() Read a byte from the file.
int	read(byte[] b) Read data from the file.
int	read(byte[] b, int off, int len) Read data from the file.
String	readLine() Read a single line of an ascii file.
int	readToEOL(byte[] b) Read until the end of line is reached.
int	readToEOL(byte[] b, int off, int len) Read until the end of line is reached.
void	seek(long off) Seek to an arbitrary offset within the file.

Methods inherited from class java.lang.Object

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

Field Detail

buffersize

public static final int buffersize

Default buffer size for uncompressed files.

zstreambuffer

public static final int zstreambuffer

Default buffer size for compressed files.

file

private File file

Open file.

stream

private RandomAccessFile stream

Stream used for uncompressed file.

zstream

private GZIPInputStream zstream

Stream used for compressed file.

buffer

private byte[] buffer

Buffer used to improve performance of small reads.

validoffset

private int validoffset

Offset of next valid data in buffer.

validlength

private int validlength

Length of valid data in buffer.

streampos

private long streampos

Current stream position.

Constructor Detail

AsciiReader

public AsciiReader(String filename)
            throws IOException

Open an uncompressed file by name.

Parameters:

filename - name of file to open

Throws:

IOException - if an error occurs openning the file

AsciiReader

public AsciiReader(String filename,
                   boolean gzip)
            throws IOException

Open an uncompressed or compressed file by name.

Parameters:

filename - name of file to open

gzip - flag to indicate if the file is GZIP compressed

Throws:

IOException - if an error occurs openning the file

Method Detail

close

public void close()

Close the data file.

finalize

protected void finalize()

Close the data file. Just calls close().

Overrides:

finalize in class Object

pushBack

public void pushBack()
              throws IOException

Push back the last byte read so it can be read again. Pushing back more that one byte is possible but is unreliable (may result in an exception).

Throws:

IOException - if the byte cannot be pushed back

read

public final int read()
               throws IOException

Read a byte from the file.

Returns:

byte read

Throws:

IOException - if an error occurs reading the file

readToEOL

public int readToEOL(byte[] b,
                     int off,
                     int len)
              throws IOException

Read until the end of line is reached. End of line is denoted by one of: '\r', '\n', or '\r\n'. If the end of line is reached, the buffer will contain one of '\r' or '\n' but not '\r\n'.

Parameters:

b - buffer where data should be placed

off - offset within buffer where data should go

len - maximum number of to be placed in buffer

Returns:

number of bytes actually read

Throws:

IOException - if an error occurs reading the file

readToEOL

public final int readToEOL(byte[] b)
                    throws IOException

Read until the end of line is reached. End of line is denoted by one of: '\r', '\n', or '\r\n'. If the end of line is reached, the buffer will contain one of '\r' or '\n' but not '\r\n'. The maximum number of characters read is b.length.

Parameters:

b - buffer where data should be placed

Returns:

number of bytes actually read

Throws:

IOException - if an error occurs reading the file

read

public int read(byte[] b,
                int off,
                int len)
         throws IOException

Read data from the file. If the size of the read is equal to or greater than buffersize, the buffer is not used and the data is read directly into b.

Parameters:

b - buffer where data should be placed

off - offset within buffer where data should go

len - maximum number of to be placed in buffer

Returns:

number of bytes read

Throws:

IOException - if an error occurs reading the file

read

public final int read(byte[] b)
               throws IOException

Read data from the file. If the size of the read is equal to or greater than buffersize, the buffer is not used and the data is read directly into b.

Parameters:

b - buffer where data should be placed

Returns:

number of bytes read

Throws:

IOException - if an error occurs reading the file

getFilePointer

public long getFilePointer()
                    throws IOException

Return the current file pointer position.

Returns:

current file position

Throws:

IOException - if an error occurs

length

public long length()

Return the length of the file. For compressed files, this method returns the compressed length. There is no way to discover the uncompressed length of a compressed file without reading (and uncompressing) the whole file.

Returns:

length of the file

seek

public void seek(long off)
          throws IOException

Seek to an arbitrary offset within the file. This method works correctly even for compressed files; however, it may be quite slow when seeking within a compressed file. For example, when seeking backwards within a compressed file, the file must be closed, reopened, and data read until the desired location is reached.

Parameters:

off - offset to seek to

Throws:

IOException - if an error occurs

readLine

public String readLine()
                throws IOException

Read a single line of an ascii file. A line is terminated with one of: '/r', '/n', or '/r/n'. The terminating character(s) are not appended to the returned string. This method is not as efficient as readToEOL().

Returns:

single ascii line as a String without the end of line characters

Throws:

IOException - if an error occurs openning the file