org.apache.commons.io.output.DeferredFileOutputStream Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.io.output;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import org.apache.commons.io.IOUtils;
/**
* 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).
*
* @author Martin Cooper
* @author gaxzerow
*
* @version $Id: DeferredFileOutputStream.java 437567 2006-08-28 06:39:07Z bayard $
*/
public class DeferredFileOutputStream
extends ThresholdingOutputStream
{
// ----------------------------------------------------------- Data members
/**
* The output stream to which data will be written prior to the theshold
* being reached.
*/
private ByteArrayOutputStream memoryOutputStream;
/**
* The output stream to which data will be written at any given time. This
* will always be one of memoryOutputStream or
* diskOutputStream.
*/
private OutputStream currentOutputStream;
/**
* The file to which output will be directed if the threshold is exceeded.
*/
private File outputFile;
/**
* True when close() has been called successfully.
*/
private boolean closed = false;
// ----------------------------------------------------------- Constructors
/**
* Constructs an instance of this class which will trigger an event at the
* specified threshold, and save data to a file beyond that point.
*
* @param threshold The number of bytes at which to trigger an event.
* @param outputFile The file to which data is saved beyond the threshold.
*/
public DeferredFileOutputStream(int threshold, File outputFile)
{
super(threshold);
this.outputFile = outputFile;
memoryOutputStream = new ByteArrayOutputStream();
currentOutputStream = memoryOutputStream;
}
// --------------------------------------- ThresholdingOutputStream methods
/**
* Returns the current output stream. This may be memory based or disk
* based, depending on the current state with respect to the threshold.
*
* @return The underlying output stream.
*
* @exception IOException if an error occurs.
*/
protected OutputStream getStream() throws IOException
{
return currentOutputStream;
}
/**
* 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.
*
* @exception IOException if an error occurs.
*/
protected void thresholdReached() throws IOException
{
FileOutputStream fos = new FileOutputStream(outputFile);
memoryOutputStream.writeTo(fos);
currentOutputStream = fos;
memoryOutputStream = null;
}
// --------------------------------------------------------- Public methods
/**
* Determines whether or not the data for this output stream has been
* retained in memory.
*
* @return true if the data is available in memory;
* false otherwise.
*/
public boolean isInMemory()
{
return (!isThresholdExceeded());
}
/**
* 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.
*
* @return The data for this output stream, or null if no such
* data is available.
*/
public byte[] getData()
{
if (memoryOutputStream != null)
{
return memoryOutputStream.toByteArray();
}
return null;
}
/**
* Returns the same output file specified in the constructor, even when
* threashold has not been reached.
*
* @return The file for this output stream, or null if no such
* file exists.
*/
public File getFile()
{
return outputFile;
}
/**
* Closes underlying output stream, and mark this as closed
*
* @exception IOException if an error occurs.
*/
public void close() throws IOException
{
super.close();
closed = true;
}
/**
* Writes the data from this output stream to the specified output stream,
* after it has been closed.
*
* @param out output stream to write to.
* @exception IOException if this stream is not yet closed or an error occurs.
*/
public void writeTo(OutputStream out) throws IOException
{
// we may only need to check if this is closed if we are working with a file
// but we should force the habit of closing wether we are working with
// a file or memory.
if (!closed)
{
throw new IOException("Stream not closed");
}
if(isInMemory())
{
memoryOutputStream.writeTo(out);
}
else
{
FileInputStream fis = new FileInputStream(outputFile);
try {
IOUtils.copy(fis, out);
} finally {
IOUtils.closeQuietly(fis);
}
}
}
}