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 280004 2005-09-10 13:19:17Z scolebourne $
Authors:
Martin Cooper
gaxzerow

Field Summary

private boolean
closed
True when close() has been called successfully.
private OutputStream
currentOutputStream
The output stream to which data will be written at any given time.
private ByteArrayOutputStream
memoryOutputStream
The output stream to which data will be written prior to the theshold being reached.
private File
outputFile
The file to which output will be directed if the threshold is exceeded.

Fields inherited from class org.apache.commons.io.output.ThresholdingOutputStream

threshold, thresholdExceeded, written

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

void
close()
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.
File
getFile()
Returns the same output file specified in the constructor, even when threashold has not been reached.
protected OutputStream
getStream()
Returns the current output stream.
boolean
isInMemory()
Determines whether or not the data for this output stream has been retained in memory.
protected void
thresholdReached()
Switches the underlying output stream from a memory based stream to one that is backed by disk.
void
writeTo(OutputStream out)
Writes the data from this output stream to the specified output stream, after it has been closed.

Methods inherited from class org.apache.commons.io.output.ThresholdingOutputStream

checkThreshold, close, flush, getByteCount, getStream, getThreshold, isThresholdExceeded, thresholdReached, write, write, write

Field Details

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 Details

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 Details

close

public void close()
            throws IOException
Closes underlying output stream, and mark this as closed
Overrides:
close in interface ThresholdingOutputStream

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()
            throws IOException
Returns the current output stream. This may be memory based or disk based, depending on the current state with respect to the threshold.
Overrides:
getStream in interface ThresholdingOutputStream
Returns:
The underlying output stream.

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()
            throws IOException
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.
Overrides:
thresholdReached in interface ThresholdingOutputStream

writeTo

public void writeTo(OutputStream out)
            throws IOException
Writes the data from this output stream to the specified output stream, after it has been closed.
Parameters:
out - output stream to write to.