org.apache.commons.io.output.DeferredFileOutputStream Maven / Gradle / Ivy
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/*
* 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.FileUtils;
import org.apache.commons.io.IOUtils;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;
import org.checkerframework.dataflow.qual.Pure;
import org.checkerframework.framework.qual.EnsuresQualifierIf;
/**
* 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 threshold
* being reached.
*/
private @Nullable 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;
// Either outputFile or prefix is non-null when a new
// DeferredFileOutputStream is created; if outputFile is null, it is
// set to non-null by thresholdReached().
/**
* The file to which output will be directed if the threshold is exceeded.
*/
private @Nullable File outputFile;
/**
* The temporary file prefix.
*/
private final @Nullable String prefix;
/**
* The temporary file suffix.
*/
private final @Nullable String suffix;
/**
* The directory to use for temporary files.
*/
private final @Nullable File directory;
/**
* 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. The initial buffer size will default to
* {@value AbstractByteArrayOutputStream#DEFAULT_SIZE} bytes which is ByteArrayOutputStream's default buffer size.
*
* @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)
{
this(threshold, outputFile, null, null, null, AbstractByteArrayOutputStream.DEFAULT_SIZE);
}
/**
* 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 initialBufferSize The initial size of the in memory buffer.
* @param outputFile The file to which data is saved beyond the threshold.
*
* @since 2.5
*/
public DeferredFileOutputStream(final int threshold, final int initialBufferSize, final File outputFile)
{
this(threshold, outputFile, null, null, null, initialBufferSize);
if (initialBufferSize < 0) {
throw new IllegalArgumentException("Initial buffer size must be atleast 0.");
}
}
/**
* 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.
* The initial buffer size will default to 32 bytes which is ByteArrayOutputStream's default buffer size.
*
* @param threshold The number of bytes at which to trigger an event.
* @param prefix Prefix to use for the temporary file.
* @param suffix Suffix to use for the temporary file.
* @param directory Temporary file directory.
*
* @since 1.4
*/
public DeferredFileOutputStream(final int threshold, final String prefix, final String suffix, final File directory)
{
this(threshold, null, prefix, suffix, directory, AbstractByteArrayOutputStream.DEFAULT_SIZE);
if (prefix == null) {
throw new IllegalArgumentException("Temporary file prefix is missing");
}
}
/**
* 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.
*
* @param threshold The number of bytes at which to trigger an event.
* @param initialBufferSize The initial size of the in memory buffer.
* @param prefix Prefix to use for the temporary file.
* @param suffix Suffix to use for the temporary file.
* @param directory Temporary file directory.
*
* @since 2.5
*/
public DeferredFileOutputStream(final int threshold, final int initialBufferSize, final String prefix,
final String suffix, final File directory)
{
this(threshold, null, prefix, suffix, directory, initialBufferSize);
if (prefix == null) {
throw new IllegalArgumentException("Temporary file prefix is missing");
}
if (initialBufferSize < 0) {
throw new IllegalArgumentException("Initial buffer size must be atleast 0.");
}
}
/**
* 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.
* @param initialBufferSize The initial size of the in memory buffer.
*/
private DeferredFileOutputStream(final int threshold, final @Nullable File outputFile, final @Nullable String prefix,
final @Nullable String suffix, final @Nullable File directory, final int initialBufferSize) {
super(threshold);
this.outputFile = outputFile;
this.prefix = prefix;
this.suffix = suffix;
this.directory = directory;
memoryOutputStream = new ByteArrayOutputStream(initialBufferSize);
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.
*
* @throws 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.
*
* @throws IOException if an error occurs.
*/
@Override
protected void thresholdReached() throws IOException
{
if (prefix != null) {
outputFile = File.createTempFile(prefix, suffix, directory);
}
assert outputFile != null : "@AssumeAssertion(nullness): constructors ensure that either prefix or outputFile is non-null";
FileUtils.forceMkdirParent(outputFile);
final FileOutputStream fos = new FileOutputStream(outputFile);
try {
// Can't do @RequiresNonNull("memoryOutputStream") because superclass has no such requirement.
assert memoryOutputStream != null
: "@AssumeAssertion(nullness): thresholdReached() is called at most once and nothing else sets memoryOutputStream to null";
memoryOutputStream.writeTo(fos);
} catch (final IOException e){
fos.close();
throw e;
}
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.
*/
@EnsuresQualifierIf(result=true, qualifier=NonNull.class, expression="memoryOutputStream")
@EnsuresQualifierIf(result=false, qualifier=NonNull.class, expression="outputFile")
@Pure
public boolean isInMemory()
{
return !isThresholdExceeded();
}
@SuppressWarnings("contracts.conditional.postcondition.not.satisfied") // application invariant; see note immediately below
// Note: a call to checkThreshold() can violate these properties by
// switching the stream from in memory to on disk, without changing the
// values that isInMemory() and isThresholdExceeded() depend upon.
// However, checkThreshold(int count) is protected, and it is never
// called without count bytes being immediately written to the stream,
// which re-establishes the invariant.
// The below is equivalent to the following:
// @EnsuresNonNullIf(expression="outputFile", result=true)
// @EnsuresNonNullIf(expression="memoryOutputStream", result=false)
// but @EnsuresNonNullIf is not repeatable (see https://tinyurl.com/cfissue/1307 ).
@EnsuresQualifierIf(result=true, qualifier=NonNull.class, expression="outputFile")
@EnsuresQualifierIf(result=false, qualifier=NonNull.class, expression="memoryOutputStream")
@Pure
public boolean isThresholdExceeded()
{
return super.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 @Nullable [] 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 @Nullable File getFile()
{
return outputFile;
}
/**
* Closes underlying output stream, and mark this as closed
*
* @throws IOException if an error occurs.
*/
@Override
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.
* @throws IOException if this stream is not yet closed or an error occurs.
*/
public void writeTo(final 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 whether we are working with
// a file or memory.
if (!closed) {
throw new IOException("Stream not closed");
}
if (isInMemory()) {
memoryOutputStream.writeTo(out);
} else {
try (FileInputStream fis = new FileInputStream(outputFile)) {
IOUtils.copy(fis, out);
}
}
}
}