org.apache.wicket.util.io.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.wicket.util.io;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import org.apache.wicket.util.lang.Args;
/**
*
* 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
*/
public class DeferredFileOutputStream extends ThresholdingOutputStream
{
/**
* 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 output stream to which data will be written prior to the threshold being reached.
*/
private ByteArrayOutputStream memoryOutputStream;
/**
* The file to which output will be directed if the threshold is exceeded.
*/
private File outputFile;
private final FileFactory fileFactory;
/**
* 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(final int threshold, final File outputFile)
{
super(threshold);
this.outputFile = Args.notNull(outputFile, "outputFile");
fileFactory = null;
memoryOutputStream = new ByteArrayOutputStream();
currentOutputStream = memoryOutputStream;
}
/**
* 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 fileFactory
* The FileFactory to create the file.
*/
public DeferredFileOutputStream(final int threshold, final FileFactory fileFactory)
{
super(threshold);
this.fileFactory = Args.notNull(fileFactory, "fileFactory");
memoryOutputStream = new ByteArrayOutputStream();
currentOutputStream = memoryOutputStream;
}
/**
* 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 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
.
*
* @return The file for this output stream, or null
if no such file exists.
*/
public File getFile()
{
return outputFile;
}
/**
* 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 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.
*/
@Override
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 realize 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.
*/
@Override
protected void thresholdReached() throws IOException
{
byte[] data = memoryOutputStream.toByteArray();
if (outputFile == null)
{
outputFile = fileFactory.createFile();
}
FileOutputStream fos = new FileOutputStream(outputFile);
fos.write(data);
currentOutputStream = fos;
memoryOutputStream = null;
}
/**
* The file factory for this deferred file output stream.
*
* @author jcompagner
*/
public interface FileFactory
{
/**
* @return the file to use for disk cache
*/
File createFile();
}
}