org.apache.tomcat.util.http.fileupload.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.tomcat.util.http.fileupload;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
/**
* 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).
*/
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;
/**
* The temporary file prefix.
*/
private final String prefix;
/**
* The temporary file suffix.
*/
private final String suffix;
/**
* The directory to use for temporary files.
*/
private final File directory;
// ----------------------------------------------------------- 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)
{
this(threshold, outputFile, null, null, null);
}
/**
* Constructs an instance of this class which will trigger an event at the
* specified threshold, and save data either 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.
* @param prefix Prefix to use for the temporary file.
* @param suffix Suffix to use for the temporary file.
* @param directory Temporary file directory.
*/
private DeferredFileOutputStream(int threshold, File outputFile, String prefix, String suffix, File directory) {
super(threshold);
this.outputFile = outputFile;
memoryOutputStream = new ByteArrayOutputStream();
currentOutputStream = memoryOutputStream;
this.prefix = prefix;
this.suffix = suffix;
this.directory = directory;
}
// --------------------------------------- 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.
*/
@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 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.
*/
@Override
protected void thresholdReached() throws IOException
{
if (prefix != null) {
outputFile = File.createTempFile(prefix, suffix, directory);
}
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 {@code true} if the data is available in memory;
* {@code 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 {@code null}.
*
* @return The data for this output stream, or {@code null} if no such
* data is available.
*/
public byte[] getData()
{
if (memoryOutputStream != null)
{
return memoryOutputStream.toByteArray();
}
return null;
}
/**
* 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 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 {@code null} is returned.
*
* @return The file for this output stream, or {@code 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.
*/
@Override
public void close() throws IOException
{
super.close();
}
}