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.
Version:
$Id: DeferredFileOutputStream.java,v 1.2 2004/02/23 04:40:29 bayard Exp $
Author:
Martin Cooper

Field Summary

private OutputStream
currentOutputStream
The output stream to which data will be written at any given time.
private FileOutputStream
diskOutputStream
The output stream to which data will be written after the theshold is reached.
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

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 data for this output stream as a File, assuming that the data was written to disk.
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.

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

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

Field Details

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.

diskOutputStream

private FileOutputStream diskOutputStream
The output stream to which data will be written after the theshold is reached.

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

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 data for this output stream as a File, assuming that the data was written to disk. If the data was retained in memory, this method returns null.
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