Java tutorial
/* * $Header: /home/cvs/jakarta-commons/fileupload/src/java/org/apache/commons/fileupload/DeferredFileOutputStream.java,v 1.2 2003/05/31 22:31:08 martinc Exp $ * $Revision: 1.2 $ * $Date: 2003/05/31 22:31:08 $ * * ==================================================================== * * The Apache Software License, Version 1.1 * * Copyright (c) 2001-2003 The Apache Software Foundation. All rights * reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. The end-user documentation included with the redistribution, if * any, must include the following acknowlegement: * "This product includes software developed by the * Apache Software Foundation (http://www.apache.org/)." * Alternately, this acknowlegement may appear in the software itself, * if and wherever such third-party acknowlegements normally appear. * * 4. The names "The Jakarta Project", "Commons", and "Apache Software * Foundation" must not be used to endorse or promote products derived * from this software without prior written permission. For written * permission, please contact apache@apache.org. * * 5. Products derived from this software may not be called "Apache" * nor may "Apache" appear in their names without prior written * permission of the Apache Group. * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * ==================================================================== * * This software consists of voluntary contributions made by many * individuals on behalf of the Apache Software Foundation. For more * information on the Apache Software Foundation, please see * <http://www.apache.org/>. * */ package org.apache.commons.fileupload; import java.io.ByteArrayOutputStream; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.OutputStream; /** * <p>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.</p> * * @author <a href="mailto:martinc@apache.org">Martin Cooper</a> * * @version $Id: DeferredFileOutputStream.java,v 1.2 2003/05/31 22:31:08 martinc Exp $ */ 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 after the theshold is * reached. */ private FileOutputStream diskOutputStream; /** * The output stream to which data will be written at any given time. This * will always be one of <code>memoryOutputStream</code> or * <code>diskOutputStream</code>. */ private OutputStream currentOutputStream; /** * The file to which output will be directed if the threshold is exceeded. */ private File outputFile; // ----------------------------------------------------------- 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(threshold); 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 { byte[] data = memoryOutputStream.toByteArray(); FileOutputStream fos = new FileOutputStream(outputFile); fos.write(data); diskOutputStream = 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</code> if the data is available in memory; * <code>false</code> 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</code>. * * @return The data for this output stream, or <code>null</code> 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 <code>File</code>, assuming * that the data was written to disk. If the data was retained in memory, * this method returns <code>null</code>. * * @return The file for this output stream, or <code>null</code> if no such * file exists. */ public File getFile() { return outputFile; } }