com.onewebsql.util.io.output
Class DeferredFileOutputStream

java.lang.Object
  extended by java.io.OutputStream
      extended by com.onewebsql.util.io.output.ThresholdingOutputStream
          extended by com.onewebsql.util.io.output.DeferredFileOutputStream
All Implemented Interfaces:
Closeable, Flushable

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).


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.
DeferredFileOutputStream(int threshold, String prefix, String suffix, File directory)
          Constructs an instance of this class which will trigger an event at the specified threshold, and save data to a temporary 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 either the output file specified in the constructor or the temporary file created or null.
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 com.onewebsql.util.io.output.ThresholdingOutputStream
checkThreshold, flush, getByteCount, getThreshold, isThresholdExceeded, resetByteCount, 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.

DeferredFileOutputStream

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

Parameters:
threshold - The number of bytes at which to trigger an event.
prefix - Prefix to use for the temporary file.
suffix - Suffix to use for the temporary file.
directory - Temporary file directory.
Since:
Commons IO 1.4
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 either the output file specified in the constructor or the temporary file created or null.

If the constructor specifying the file is used then it returns that same output file, even when threashold has not been reached.

If constructor specifying a temporary file prefix/suffix is used then the temporary file created once the threashold is reached is returned If the threshold was not reached then null is returned.

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

Specified by:
close in interface Closeable
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.


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