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

All Implemented Interfaces:

Closeable, Flushable, AutoCloseable

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.

To build an instance, use DeferredFileOutputStream.Builder.

The caller is responsible for deleting the output file (getFile(), getPath()) created by a DeferredFileOutputStream when the caller only configured a prefix.

The caller is responsible for deleting the output file passed to a constructor or builder through DeferredFileOutputStream.Builder.setOutputFile(File) or DeferredFileOutputStream.Builder.setOutputFile(Path).

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).

See Also:

DeferredFileOutputStream.Builder

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	DeferredFileOutputStream.Builder Builds a new DeferredFileOutputStream.

Method Summary

Modifier and Type	Method and Description
static DeferredFileOutputStream.Builder	builder() Constructs a new DeferredFileOutputStream.Builder.
void	close() Closes underlying output stream, and mark this as closed
byte[]	getData() Gets the data for this output stream as an array of bytes, assuming that the data has been retained in memory.
File	getFile() Gets either the output File specified in the constructor or the temporary File created or null.
Path	getPath() Gets either the output Path specified in the constructor or the temporary Path created or null.
boolean	isInMemory() Tests 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.
InputStream	toInputStream() Converts the current contents of this byte stream to an InputStream.
void	writeTo(OutputStream outputStream) 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, getOutputStream, getThreshold, isThresholdExceeded, resetByteCount, setByteCount, write, write, write

Methods inherited from class java.lang.Object

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

Method Detail

builder

public static DeferredFileOutputStream.Builder builder()

Constructs a new DeferredFileOutputStream.Builder.

Returns:

a new DeferredFileOutputStream.Builder.

close

public void close()
           throws IOException

Closes underlying output stream, and mark this as closed

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Overrides:

close in class ThresholdingOutputStream

Throws:

IOException - if an error occurs.

getData

public byte[] getData()

Gets 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()

Gets 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 threshold has not been reached.

If constructor specifying a temporary File prefix/suffix is used then the temporary File created once the threshold 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.

getPath

public Path getPath()

Gets either the output Path specified in the constructor or the temporary Path created or null.

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

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

Returns:

The Path for this output stream, or null if no such Path exists.

isInMemory

public boolean isInMemory()

Tests 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 realize that too much data is being written to keep in memory, so we elect to switch to disk-based storage.

Overrides:

thresholdReached in class ThresholdingOutputStream

Throws:

IOException - if an error occurs.

toInputStream

public InputStream toInputStream()
                          throws IOException

Converts the current contents of this byte stream to an InputStream. If the data for this output stream has been retained in memory, the returned stream is backed by buffers of this stream, avoiding memory allocation and copy, thus saving space and time.
Otherwise, the returned stream will be one that is created from the data that has been committed to disk.

Returns:

the current contents of this output stream.

Throws:

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

See Also:

ByteArrayOutputStream.toInputStream()

writeTo

public void writeTo(OutputStream outputStream)
             throws IOException

Writes the data from this output stream to the specified output stream, after it has been closed.

Parameters:

outputStream - output stream to write to.

Throws:

NullPointerException - if the OutputStream is null.

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