org.apache.commons.io.output
Class DeferredFileOutputStream

java.lang.Object
  java.io.OutputStream
      org.apache.commons.io.output.ThresholdingOutputStream
          org.apache.commons.io.output.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 $

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, flush, getByteCount, getThreshold, isThresholdExceeded, write, write, write

Methods inherited from class java.lang.Object

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

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

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.

Specified by:

getStream in class ThresholdingOutputStream

Returns:

The underlying output stream.

Throws:

IOException - if an error occurs.

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.

Specified by:

thresholdReached in class ThresholdingOutputStream

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.

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.

close

public void close()
           throws IOException

Closes underlying output stream, and mark this as closed

Overrides:

close in class ThresholdingOutputStream

Throws:

IOException - if an error occurs.

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.

Throws:

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