alfresco-community-repo/source/java/org/alfresco/repo/content/AbstractContentWriter.java

/*
 * Copyright (C) 2005 Alfresco, Inc.
 *
 * Licensed under the Mozilla Public License version 1.1 
 * with a permitted attribution clause. You may obtain a
 * copy of the License at
 *
 *   http://www.alfresco.org/legal/license.txt
 *
 * 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.alfresco.repo.content;

import java.io.BufferedOutputStream;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.WritableByteChannel;
import java.util.ArrayList;
import java.util.List;

import org.alfresco.error.AlfrescoRuntimeException;
import org.alfresco.repo.content.filestore.FileContentWriter;
import org.alfresco.service.cmr.repository.ContentAccessor;
import org.alfresco.service.cmr.repository.ContentIOException;
import org.alfresco.service.cmr.repository.ContentReader;
import org.alfresco.service.cmr.repository.ContentStreamListener;
import org.alfresco.service.cmr.repository.ContentWriter;
import org.alfresco.util.TempFileProvider;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.aop.framework.ProxyFactory;
import org.springframework.util.FileCopyUtils;

/**
 * Implements all the convenience methods of the interface.  The only methods
 * that need to be implemented, i.e. provide low-level content access are:
 * <ul>
 *   <li>{@link #getDirectWritableChannel()} to write content to the repository</li>
 * </ul>
 * 
 * @author Derek Hulley
 */
public abstract class AbstractContentWriter extends AbstractContentAccessor implements ContentWriter
{
    private static final Log logger = LogFactory.getLog(AbstractContentWriter.class);
    
    private List<ContentStreamListener> listeners;
    private WritableByteChannel channel;
    private ContentReader existingContentReader;
    
    /**
     * @param contentUrl the content URL
     * @param existingContentReader a reader of a previous version of this content
     */
    protected AbstractContentWriter(String contentUrl, ContentReader existingContentReader)
    {
        super(contentUrl);
        this.existingContentReader = existingContentReader;
        
        listeners = new ArrayList<ContentStreamListener>(2);
    }

    /**
     * @return Returns a reader onto the previous version of this content
     */
    protected ContentReader getExistingContentReader()
    {
        return existingContentReader;
    }

    /**
     * Adds the listener after checking that the output stream isn't already in
     * use.
     */
    public synchronized void addListener(ContentStreamListener listener)
    {
        if (channel != null)
        {
            throw new RuntimeException("Channel is already in use");
        }
        listeners.add(listener);
    }

    /**
     * A factory method for subclasses to implement that will ensure the proper
     * implementation of the {@link ContentWriter#getReader()} method.
     * <p>
     * Only the instance need be constructed.  The required mimetype, encoding, etc
     * will be copied across by this class.
     * <p>
     *  
     * @return Returns a reader onto the location referenced by this instance.
     *      The instance must <b>always</b> be a new instance and never null.
     * @throws ContentIOException
     */
    protected abstract ContentReader createReader() throws ContentIOException;
    
    /**
     * Performs checks and copies required reader attributes
     */
    public final ContentReader getReader() throws ContentIOException
    {
        if (!isClosed())
        {
            return null;
        }
        ContentReader reader = createReader();
        if (reader == null)
        {
            throw new AlfrescoRuntimeException("ContentReader failed to create new reader: \n" +
                    "   writer: " + this);
        }
        else if (reader.getContentUrl() == null || !reader.getContentUrl().equals(getContentUrl()))
        {
            throw new AlfrescoRuntimeException("ContentReader has different URL: \n" +
                    "   writer: " + this + "\n" +
                    "   new reader: " + reader);
        }
        // copy across common attributes
        reader.setMimetype(this.getMimetype());
        reader.setEncoding(this.getEncoding());
        // done
        if (logger.isDebugEnabled())
        {
            logger.debug("Writer spawned new reader: \n" +
                    "   writer: " + this + "\n" +
                    "   new reader: " + reader);
        }
        return reader;
    }

    /**
     * An automatically created listener sets the flag
     */
    public synchronized final boolean isClosed()
    {
        if (channel != null)
        {
            return !channel.isOpen();
        }
        else
        {
            return false;
        }
    }

    public synchronized boolean isChannelOpen()
    {
        if (channel != null)
        {
            return channel.isOpen();
        }
        else
        {
            return false;
        }
    }
    
    /**
     * Provides low-level access to write content to the repository.
     * <p>
     * This is the only of the content <i>writing</i> methods that needs to be implemented
     * by derived classes.  All other content access methods make use of this in their
     * underlying implementations.
     * 
     * @return Returns a channel with which to write content
     * @throws ContentIOException if the channel could not be opened
     */
    protected abstract WritableByteChannel getDirectWritableChannel() throws ContentIOException;
    
    /**
     * Create a channel that performs callbacks to the given listeners.
     *  
     * @param directChannel the result of {@link #getDirectWritableChannel()}
     * @param listeners the listeners to call
     * @return Returns a channel that executes callbacks
     * @throws ContentIOException
     */
    private WritableByteChannel getCallbackWritableChannel(
            WritableByteChannel directChannel,
            List<ContentStreamListener> listeners)
            throws ContentIOException
    {
        WritableByteChannel callbackChannel = null;
        if (directChannel instanceof FileChannel)
        {
            callbackChannel = getCallbackFileChannel((FileChannel) directChannel, listeners);
        }
        else
        {
            // introduce an advistor to handle the callbacks to the listeners
            ChannelCloseCallbackAdvise advise = new ChannelCloseCallbackAdvise(listeners);
            ProxyFactory proxyFactory = new ProxyFactory(directChannel);
            proxyFactory.addAdvice(advise);
            callbackChannel = (WritableByteChannel) proxyFactory.getProxy();
        }
        // done
        if (logger.isDebugEnabled())
        {
            logger.debug("Created callback byte channel: \n" +
                    "   original: " + directChannel + "\n" +
                    "   new: " + callbackChannel);
        }
        return callbackChannel;
    }

    /**
     * @see #getDirectWritableChannel()
     * @see #getCallbackWritableChannel()
     */
    public synchronized final WritableByteChannel getWritableChannel() throws ContentIOException
    {
        // this is a use-once object
        if (channel != null)
        {
            throw new RuntimeException("A channel has already been opened");
        }
        WritableByteChannel directChannel = getDirectWritableChannel();
        channel = getCallbackWritableChannel(directChannel, listeners);

        // notify that the channel was opened
        super.channelOpened();
        // done
        if (logger.isDebugEnabled())
        {
            logger.debug("Opened channel onto content: \n" +
                    "   content: " + this + "\n" +
                    "   channel: " + channel);
        }
        return channel;
    }
    
    /**
     * @inheritDoc
     */
    public FileChannel getFileChannel(boolean truncate) throws ContentIOException
    {
        /*
         * By calling this method, clients indicate that they wish to make random
         * changes to the file.  It is possible that the client might only want
         * to update a tiny proportion of the file (truncate == false) or
         * start afresh (truncate == true).
         * 
         * Where the underlying support is not present for this method, a temporary
         * file will be used as a substitute.  When the write is complete, the
         * results are copied directly to the underlying channel.
         */
        
        // get the underlying implementation's best writable channel
        channel = getWritableChannel();
        // now use this channel if it can provide the random access, otherwise spoof it
        FileChannel clientFileChannel = null;
        if (channel instanceof FileChannel)
        {
            // all the support is provided by the underlying implementation
            clientFileChannel = (FileChannel) channel;
            // copy over the existing content, if required
            if (!truncate && existingContentReader != null)
            {
                ReadableByteChannel existingContentChannel = existingContentReader.getReadableChannel();
                long existingContentLength = existingContentReader.getSize();
                // copy the existing content
                try
                {
                    clientFileChannel.transferFrom(existingContentChannel, 0, existingContentLength);
                    // copy complete
                    if (logger.isDebugEnabled())
                    {
                        logger.debug("Copied content for random access: \n" +
                                "   writer: " + this + "\n" +
                                "   existing: " + existingContentReader);
                    }
                }
                catch (IOException e)
                {
                    throw new ContentIOException("Failed to copy from existing content to enable random access: \n" +
                            "   writer: " + this + "\n" +
                            "   existing: " + existingContentReader,
                            e);
                }
                finally
                {
                    try { existingContentChannel.close(); } catch (IOException e) {}
                }
            }
            // debug
            if (logger.isDebugEnabled())
            {
                logger.debug("Content writer provided direct support for FileChannel: \n" +
                        "   writer: " + this);
            }
        }
        else
        {
            // No random access support is provided by the implementation.
            // Spoof it by providing a 2-stage write via a temp file
            File tempFile = TempFileProvider.createTempFile("random_write_spoof_", ".bin");
            final FileContentWriter spoofWriter = new FileContentWriter(
                    tempFile,                           // the file to write to
                    getExistingContentReader());        // this ensures that the existing content is pulled in
            // Attach a listener
            // - to ensure that the content gets loaded from the temp file once writing has finished
            // - to ensure that the close call gets passed on to the underlying channel
            ContentStreamListener spoofListener = new ContentStreamListener()
            {
                public void contentStreamClosed() throws ContentIOException
                {
                    // the spoofed temp channel has been closed, so get a new reader for it
                    ContentReader spoofReader = spoofWriter.getReader();
                    FileChannel spoofChannel = spoofReader.getFileChannel();
                    // upload all the temp content to the real underlying channel
                    try
                    {
                        long spoofFileSize = spoofChannel.size();
                        spoofChannel.transferTo(0, spoofFileSize, channel);
                    }
                    catch (IOException e)
                    {
                        throw new ContentIOException("Failed to copy from spoofed temporary channel to permanent channel: \n" +
                                "   writer: " + this + "\n" +
                                "   temp: " + spoofReader,
                                e);
                    }
                    finally
                    {
                        try { spoofChannel.close(); } catch (Throwable e) {}
                        try
                        {
                            channel.close();
                        }
                        catch (IOException e)
                        {
                            throw new ContentIOException("Failed to close underlying channel", e);
                        }
                    }
                }
            };
            spoofWriter.addListener(spoofListener);
            // we now have the spoofed up channel that the client can work with
            clientFileChannel = spoofWriter.getFileChannel(truncate);
            // debug
            if (logger.isDebugEnabled())
            {
                logger.debug("Content writer provided indirect support for FileChannel: \n" +
                        "   writer: " + this + "\n" +
                        "   temp writer: " + spoofWriter);
            }
        }
        // the file is now available for random access
        return clientFileChannel;
    }

    /**
     * @see Channels#newOutputStream(java.nio.channels.WritableByteChannel)
     */
    public OutputStream getContentOutputStream() throws ContentIOException
    {
        try
        {
            WritableByteChannel channel = getWritableChannel();
            OutputStream is = new BufferedOutputStream(Channels.newOutputStream(channel));
            // done
            return is;
        }
        catch (Throwable e)
        {
            throw new ContentIOException("Failed to open stream onto channel: \n" +
                    "   writer: " + this,
                    e);
        }
    }

    /**
     * @see ContentReader#getContentInputStream()
     * @see #putContent(InputStream) 
     */
    public void putContent(ContentReader reader) throws ContentIOException
    {
        try
        {
            // get the stream to read from
            InputStream is = reader.getContentInputStream();
            // put the content
            putContent(is);
        }
        catch (Throwable e)
        {
            throw new ContentIOException("Failed to copy reader content to writer: \n" +
                    "   writer: " + this + "\n" +
                    "   source reader: " + reader,
                    e);
        }
    }

    public final void putContent(InputStream is) throws ContentIOException
    {
        try
        {
            OutputStream os = getContentOutputStream();
            FileCopyUtils.copy(is, os);     // both streams are closed
            // done
        }
        catch (IOException e)
        {
            throw new ContentIOException("Failed to copy content from input stream: \n" +
                    "   writer: " + this,
                    e);
        }
    }
    
    public final void putContent(File file) throws ContentIOException
    {
        try
        {
            OutputStream os = getContentOutputStream();
            FileInputStream is = new FileInputStream(file);
            FileCopyUtils.copy(is, os);     // both streams are closed
            // done
        }
        catch (IOException e)
        {
            throw new ContentIOException("Failed to copy content from file: \n" +
                    "   writer: " + this + "\n" +
                    "   file: " + file,
                    e);
        }
    }
    
    /**
     * Makes use of the encoding, if available, to convert the string to bytes.
     * 
     * @see ContentAccessor#getEncoding()
     */
    public final void putContent(String content) throws ContentIOException
    {
        try
        {
            // attempt to use the correct encoding
            String encoding = getEncoding();
            byte[] bytes = (encoding == null) ? content.getBytes() : content.getBytes(encoding);
            // get the stream
            OutputStream os = getContentOutputStream();
            ByteArrayInputStream is = new ByteArrayInputStream(bytes);
            FileCopyUtils.copy(is, os);     // both streams are closed
            // done
        }
        catch (IOException e)
        {
            throw new ContentIOException("Failed to copy content from string: \n" +
                    "   writer: " + this +
                    "   content length: " + content.length(),
                    e);
        }
    }
}