de.unibi.techfak.jpredictor.sequences
Class ResetableReader

java.lang.Object
  java.io.Reader
      de.unibi.techfak.jpredictor.sequences.ResetableReader

All Implemented Interfaces:

java.io.Closeable, java.lang.Readable

public class ResetableReader
extends java.io.Reader

This class is designed for only one purpose: to make sure, mark and reset function on a stream. To fulfill this task, you cannot construct this class other than give a filename, which is used to reopen the file if necessary. All attempts to reset and mark are redirected to the underlying BufferedReader and only if it fails, the class' own handling takes over.

Field Summary

protected long	countReadBytes The number of actual read bytes from the underlying reader, set by read(char[], int, int), skip(int) and read().
private java.lang.String	filename The name of the file this reader is working with.
protected long	mark The mark on the underlying Reader, set by mark(int) and used by reset() to read ahead to this position.
private java.io.Reader	reader The file reader all reads are done through.

Fields inherited from class java.io.Reader

lock

Constructor Summary

ResetableReader(java.lang.String filename)
Constructs a new ResetableReader object by opening the file with new BufferedReader(new FileReader( filename ))

Method Summary

void	close() Closes this Reader.
void	mark(int readAheadLimit) Sets a mark on this stream.
boolean	markSupported() This class supports mark and reset on the stream by reopening the underlying BufferedReader if necessary.
int	read() Reads a character from the file through the underlying BufferedReader.
int	read(char[] buffer, int offset, int length) Reads characters from the file through the underlying BufferedReader and writes them into the buffer.
boolean	ready() Tells whether this stream is ready to be read.
void	reset() Resets this reader.
long	skip(long n) Skip characters.

Methods inherited from class java.io.Reader

read, read

Methods inherited from class java.lang.Object

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

Field Detail

filename

private java.lang.String filename

The name of the file this reader is working with.

reader

private java.io.Reader reader

The file reader all reads are done through.

countReadBytes

protected long countReadBytes

The number of actual read bytes from the underlying reader, set by read(char[], int, int), skip(int) and read().

mark

protected long mark

The mark on the underlying Reader, set by mark(int) and used by reset() to read ahead to this position.

Constructor Detail

ResetableReader

public ResetableReader(java.lang.String filename)
                throws java.io.FileNotFoundException,
                       java.lang.NullPointerException

Constructs a new ResetableReader object by opening the file with new BufferedReader(new FileReader( filename ))

Parameters:

filename - The filename of the file to open.

Throws:

java.io.FileNotFoundException - If the file does not exists.

java.lang.NullPointerException - If filename is null.

Method Detail

read

public int read()
         throws java.io.IOException

Reads a character from the file through the underlying BufferedReader.

Overrides:

read in class java.io.Reader

Returns:

The next valid character, -1 in case of EOF

Throws:

java.io.IOException - From the underlying BufferedReader.

See Also:

BufferedReader.read()

read

public int read(char[] buffer,
                int offset,
                int length)
         throws java.io.IOException

Reads characters from the file through the underlying BufferedReader and writes them into the buffer.

Specified by:

read in class java.io.Reader

Parameters:

buffer - The buffer to write to.

offset - The start of the buffer.

length - Number of characters to read maximal.

Returns:

The number of valid characters written into the buffer. -1 is returned if no character could be read due to a EOF.

Throws:

java.io.IOException - From the underlying BufferedReader.

close

public void close()
           throws java.io.IOException

Closes this Reader.

Specified by:

close in interface java.io.Closeable

Specified by:

close in class java.io.Reader

Throws:

java.io.IOException - From the underlying BufferedReader.

markSupported

public boolean markSupported()

This class supports mark and reset on the stream by reopening the underlying BufferedReader if necessary.

Overrides:

markSupported in class java.io.Reader

Returns:

true.

mark

public void mark(int readAheadLimit)
          throws java.io.IOException

Sets a mark on this stream. After performing a reset() it is garantied, that the next readable character is the one a read would return now.
The parameter is forwarded to the underlying BufferedReader , but if it is less than 64k, 64k is taken.

Overrides:

mark in class java.io.Reader

Parameters:

readAheadLimit - The number of characters to read until the mark on the stream expires.

Throws:

java.io.IOException - Never.

reset

public void reset()
           throws java.io.IOException

Resets this reader. The attempt to reset this reader is redirected to the underlying BufferedReader. But, since BufferedReader will always reset to the same mark and is unable to reset to the beginning of the file, the redirection policy holds only in case the mark on the reader is not zero. Thus, if the reset redirection fails or if the mark is zero the file is reopened and, if neccessary, read to the mark.

Afterwards, the mark on this Reader is set back to zero (BufferedReader would not do so and this is exactly the reason why it will always reset to the same mark once set). An attempt to reset this reader without a previously mark will reset it to the beginning, which means that the file is reopened. With all this in mind it is clear, that two subsequent calls to reset() will always set the reader to the beginning.

Overrides:

reset in class java.io.Reader

Throws:

java.io.IOException - If the file could not be reopened, or if the reopened stream could not be read to the mark.

skip

public long skip(long n)
          throws java.io.IOException

Skip characters. This call is redirected to the underlying BufferReader.

Overrides:

skip in class java.io.Reader

Parameters:

n - The number of characters to skip

Returns:

The number of characters actually skipped

Throws:

java.lang.IllegalArgumentException - If n is negative.

java.io.IOException - If an I/O error occurs.

ready

public boolean ready()
              throws java.io.IOException

Tells whether this stream is ready to be read. This call is simple forwarded to the underlying BufferedReader

Overrides:

ready in class java.io.Reader

Returns:

true if the next read() is guaranteed not to block for input, false otherwise. Note that returning false does not guarantee that the next read will block.

Throws:

java.io.IOException - If an I/O error occurs