org.apache.commons.io.output

Class DeferredFileOutputStream

public class DeferredFileOutputStream extends ThresholdingOutputStream

An output stream which will retain data in memory until a specified threshold is reached, and only then commit it to disk. If the stream is closed before the threshold is reached, the data will not be written to disk at all.

This class originated in FileUpload processing. In this use case, you do not know in advance the size of the file being uploaded. If the file is small you want to store it in memory (for speed), but if the file is large you want to store it to file (to avoid memory issues).

Version: $Id: DeferredFileOutputStream.java 437567 2006-08-28 06:39:07Z bayard $

Author: Martin Cooper gaxzerow

Field Summary
booleanclosed
True when close() has been called successfully.
OutputStreamcurrentOutputStream
The output stream to which data will be written at any given time.
ByteArrayOutputStreammemoryOutputStream
The output stream to which data will be written prior to the theshold being reached.
FileoutputFile
The file to which output will be directed if the threshold is exceeded.
Constructor Summary
DeferredFileOutputStream(int threshold, File outputFile)
Constructs an instance of this class which will trigger an event at the specified threshold, and save data to a file beyond that point.
Method Summary
voidclose()
Closes underlying output stream, and mark this as closed
byte[]getData()
Returns the data for this output stream as an array of bytes, assuming that the data has been retained in memory.
FilegetFile()
Returns the same output file specified in the constructor, even when threashold has not been reached.
protected OutputStreamgetStream()
Returns the current output stream.
booleanisInMemory()
Determines whether or not the data for this output stream has been retained in memory.
protected voidthresholdReached()
Switches the underlying output stream from a memory based stream to one that is backed by disk.
voidwriteTo(OutputStream out)
Writes the data from this output stream to the specified output stream, after it has been closed.

Field Detail

closed

private boolean closed
True when close() has been called successfully.

currentOutputStream

private OutputStream currentOutputStream
The output stream to which data will be written at any given time. This will always be one of memoryOutputStream or diskOutputStream.

memoryOutputStream

private ByteArrayOutputStream memoryOutputStream
The output stream to which data will be written prior to the theshold being reached.

outputFile

private File outputFile
The file to which output will be directed if the threshold is exceeded.

Constructor Detail

DeferredFileOutputStream

public DeferredFileOutputStream(int threshold, File outputFile)
Constructs an instance of this class which will trigger an event at the specified threshold, and save data to a file beyond that point.

Parameters: threshold The number of bytes at which to trigger an event. outputFile The file to which data is saved beyond the threshold.

Method Detail

close

public void close()
Closes underlying output stream, and mark this as closed

Throws: IOException if an error occurs.

getData

public byte[] getData()
Returns the data for this output stream as an array of bytes, assuming that the data has been retained in memory. If the data was written to disk, this method returns null.

Returns: The data for this output stream, or null if no such data is available.

getFile

public File getFile()
Returns the same output file specified in the constructor, even when threashold has not been reached.

Returns: The file for this output stream, or null if no such file exists.

getStream

protected OutputStream getStream()
Returns the current output stream. This may be memory based or disk based, depending on the current state with respect to the threshold.

Returns: The underlying output stream.

Throws: IOException if an error occurs.

isInMemory

public boolean isInMemory()
Determines whether or not the data for this output stream has been retained in memory.

Returns: true if the data is available in memory; false otherwise.

thresholdReached

protected void thresholdReached()
Switches the underlying output stream from a memory based stream to one that is backed by disk. This is the point at which we realise that too much data is being written to keep in memory, so we elect to switch to disk-based storage.

Throws: IOException if an error occurs.

writeTo

public void writeTo(OutputStream out)
Writes the data from this output stream to the specified output stream, after it has been closed.

Parameters: out output stream to write to.

Throws: IOException if this stream is not yet closed or an error occurs.