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Commons IO example source code file (DeferredFileOutputStream.java)

This example Commons IO source code file (DeferredFileOutputStream.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons IO tags/keywords

bytearrayoutputstream, deferredfileoutputstream, deferredfileoutputstream, file, file, fileinputstream, fileoutputstream, io, ioexception, ioexception, outputstream, override, string, string, thresholdingoutputstream

The Commons IO DeferredFileOutputStream.java source code

/*
 * 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
 * @author gaxzerow
 *
 * @version $Id: DeferredFileOutputStream.java 736890 2009-01-23 02:02:22Z niallp $
 */
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 or
     * <code>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;

    
    /**
     * 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)
    {
        this(threshold,  outputFile, null, null, null);
    }


    /**
     * 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,   null, prefix, suffix, directory);
        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 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.
     * <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 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();
        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);
            }
        }
    }
}

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