Java tutorial
/* * 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. * <p> * 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 <a href="mailto:martinc@apache.org">Martin Cooper</a> * @author gaxzerow * * @version $Id: DeferredFileOutputStream.java 606381 2007-12-22 02:03:16Z ggregory $ */ 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 <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; /** * The temporary file prefix. */ private String prefix; /** * The temporary file suffix. */ private String suffix; /** * The directory to use for temporary files. */ private 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. * * @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; } /** * 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 prefix Prefix to use for the temporary file. * @param suffix Suffix to use for the temporary file. * @param directory Temporary file directory. * * @since Commons IO 1.4 */ public DeferredFileOutputStream(int threshold, String prefix, String suffix, File directory) { this(threshold, (File) null); if (prefix == null) { throw new IllegalArgumentException("Temporary file prefix is missing"); } 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. */ 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 { 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</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 either the output file specified in the constructor or * the temporary file created or null. * <p> * If the constructor specifying the file is used then it returns that * same output file, even when threashold has not been reached. * <p> * If constructor specifying a temporary file prefix/suffix is used * then the temporary file created once the threashold is reached is returned * If the threshold was not reached then <code>null</code> is returned. * * @return The file for this output stream, or <code>null</code> 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); } } } }