org.apache.commons.io.output
Class LockableFileWriter

java.lang.Object
  java.io.Writer
      org.apache.commons.io.output.LockableFileWriter

All Implemented Interfaces:

java.io.Closeable, java.io.Flushable, java.lang.Appendable

public class LockableFileWriter
extends java.io.Writer

FileWriter that will create and honor lock files to allow simple cross thread file lock handling.

This class provides a simple alternative to FileWriter that will use a lock file to prevent duplicate writes.

By default, the file will be overwritten, but this may be changed to append. The lock directory may be specified, but defaults to the system property java.io.tmpdir. The encoding may also be specified, and defaults to the platform default.

Version:

$Id: LockableFileWriter.java 610010 2008-01-08 14:50:59Z niallp $

Author:

Scott Sanders, Michael Salmon, Jon S. Stevens, Daniel Rall, Stephen Colebourne, Andy Lehane

Field Summary

private static java.lang.String	LCK The extension for the lock file.
private java.io.File	lockFile The lock file.
private java.io.Writer	out The writer to decorate.

Fields inherited from class java.io.Writer

lock

Constructor Summary

LockableFileWriter(java.io.File file)
Constructs a LockableFileWriter.

LockableFileWriter(java.io.File file, boolean append)
Constructs a LockableFileWriter.

LockableFileWriter(java.io.File file, boolean append, java.lang.String lockDir)
Constructs a LockableFileWriter.

LockableFileWriter(java.io.File file, java.lang.String encoding)
Constructs a LockableFileWriter with a file encoding.

LockableFileWriter(java.io.File file, java.lang.String encoding, boolean append, java.lang.String lockDir)
Constructs a LockableFileWriter with a file encoding.

LockableFileWriter(java.lang.String fileName)
Constructs a LockableFileWriter.

LockableFileWriter(java.lang.String fileName, boolean append)
Constructs a LockableFileWriter.

LockableFileWriter(java.lang.String fileName, boolean append, java.lang.String lockDir)
Constructs a LockableFileWriter.

Method Summary

void	close() Closes the file writer.
private void	createLock() Creates the lock file.
void	flush() Flush the stream.
private java.io.Writer	initWriter(java.io.File file, java.lang.String encoding, boolean append) Initialise the wrapped file writer.
private void	testLockDir(java.io.File lockDir) Tests that we can write to the lock directory.
void	write(char[] chr) Write the characters from an array.
void	write(char[] chr, int st, int end) Write the specified characters from an array.
void	write(int idx) Write a character.
void	write(java.lang.String str) Write the characters from a string.
void	write(java.lang.String str, int st, int end) Write the specified characters from a string.

Methods inherited from class java.io.Writer

append, append, append

Methods inherited from class java.lang.Object

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

Field Detail

LCK

private static final java.lang.String LCK

The extension for the lock file.

See Also:

Constant Field Values

out

private final java.io.Writer out

The writer to decorate.

lockFile

private final java.io.File lockFile

The lock file.

Constructor Detail

LockableFileWriter

public LockableFileWriter(java.lang.String fileName)
                   throws java.io.IOException

Constructs a LockableFileWriter. If the file exists, it is overwritten.

Parameters:

fileName - the file to write to, not null

Throws:

java.lang.NullPointerException - if the file is null

java.io.IOException - in case of an I/O error

LockableFileWriter

public LockableFileWriter(java.lang.String fileName,
                          boolean append)
                   throws java.io.IOException

Constructs a LockableFileWriter.

Parameters:

fileName - file to write to, not null

append - true if content should be appended, false to overwrite

Throws:

java.lang.NullPointerException - if the file is null

java.io.IOException - in case of an I/O error

LockableFileWriter

public LockableFileWriter(java.lang.String fileName,
                          boolean append,
                          java.lang.String lockDir)
                   throws java.io.IOException

Constructs a LockableFileWriter.

Parameters:

fileName - the file to write to, not null

append - true if content should be appended, false to overwrite

lockDir - the directory in which the lock file should be held

Throws:

java.lang.NullPointerException - if the file is null

java.io.IOException - in case of an I/O error

LockableFileWriter

public LockableFileWriter(java.io.File file)
                   throws java.io.IOException

Constructs a LockableFileWriter. If the file exists, it is overwritten.

Parameters:

file - the file to write to, not null

Throws:

java.lang.NullPointerException - if the file is null

java.io.IOException - in case of an I/O error

LockableFileWriter

public LockableFileWriter(java.io.File file,
                          boolean append)
                   throws java.io.IOException

Constructs a LockableFileWriter.

Parameters:

file - the file to write to, not null

append - true if content should be appended, false to overwrite

Throws:

java.lang.NullPointerException - if the file is null

java.io.IOException - in case of an I/O error

LockableFileWriter

public LockableFileWriter(java.io.File file,
                          boolean append,
                          java.lang.String lockDir)
                   throws java.io.IOException

Constructs a LockableFileWriter.

Parameters:

file - the file to write to, not null

append - true if content should be appended, false to overwrite

lockDir - the directory in which the lock file should be held

Throws:

java.lang.NullPointerException - if the file is null

java.io.IOException - in case of an I/O error

LockableFileWriter

public LockableFileWriter(java.io.File file,
                          java.lang.String encoding)
                   throws java.io.IOException

Constructs a LockableFileWriter with a file encoding.

Parameters:

file - the file to write to, not null

encoding - the encoding to use, null means platform default

Throws:

java.lang.NullPointerException - if the file is null

java.io.IOException - in case of an I/O error

LockableFileWriter

public LockableFileWriter(java.io.File file,
                          java.lang.String encoding,
                          boolean append,
                          java.lang.String lockDir)
                   throws java.io.IOException

Constructs a LockableFileWriter with a file encoding.

Parameters:

file - the file to write to, not null

encoding - the encoding to use, null means platform default

append - true if content should be appended, false to overwrite

lockDir - the directory in which the lock file should be held

Throws:

java.lang.NullPointerException - if the file is null

java.io.IOException - in case of an I/O error

Method Detail

testLockDir

private void testLockDir(java.io.File lockDir)
                  throws java.io.IOException

Tests that we can write to the lock directory.

Parameters:

lockDir - the File representing the lock directory

Throws:

java.io.IOException - if we cannot write to the lock directory

java.io.IOException - if we cannot find the lock file

createLock

private void createLock()
                 throws java.io.IOException

Creates the lock file.

Throws:

java.io.IOException - if we cannot create the file

initWriter

private java.io.Writer initWriter(java.io.File file,
                                  java.lang.String encoding,
                                  boolean append)
                           throws java.io.IOException

Initialise the wrapped file writer. Ensure that a cleanup occurs if the writer creation fails.

Parameters:

file - the file to be accessed

encoding - the encoding to use

append - true to append

Returns:

The initialised writer

Throws:

java.io.IOException - if an error occurs

close

public void close()
           throws java.io.IOException

Closes the file writer.

Specified by:

close in interface java.io.Closeable

Specified by:

close in class java.io.Writer

Throws:

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

write

public void write(int idx)
           throws java.io.IOException

Write a character.

Overrides:

write in class java.io.Writer

Parameters:

idx - the character to write

Throws:

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

write

public void write(char[] chr)
           throws java.io.IOException

Write the characters from an array.

Overrides:

write in class java.io.Writer

Parameters:

chr - the characters to write

Throws:

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

write

public void write(char[] chr,
                  int st,
                  int end)
           throws java.io.IOException

Write the specified characters from an array.

Specified by:

write in class java.io.Writer

Parameters:

chr - the characters to write

st - The start offset

end - The number of characters to write

Throws:

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

write

public void write(java.lang.String str)
           throws java.io.IOException

Write the characters from a string.

Overrides:

write in class java.io.Writer

Parameters:

str - the string to write

Throws:

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

write

public void write(java.lang.String str,
                  int st,
                  int end)
           throws java.io.IOException

Write the specified characters from a string.

Overrides:

write in class java.io.Writer

Parameters:

str - the string to write

st - The start offset

end - The number of characters to write

Throws:

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

flush

public void flush()
           throws java.io.IOException

Flush the stream.

Specified by:

flush in interface java.io.Flushable

Specified by:

flush in class java.io.Writer

Throws:

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