Examples of java.nio.channels.FileChannel

java.nio.channels.FileChannel
An abstract channel type for interaction with a platform file.
A FileChannel defines the methods for reading, writing, memory mapping, and manipulating the logical state of a platform file. This type does not have a method for opening files, since this behaviour has been delegated to the FileInputStream, FileOutputStream, and RandomAccessFile types.

FileChannels created from a FileInputStream, or a RandomAccessFile created in mode "r", are read-only. FileChannels created from a FileOutputStream are write-only. FileChannels created from a RandomAccessFile created in mode "rw" are read/write. FileChannels created from a RandomAccessFile that was opened in append-mode will also be in append-mode -- meaning that each write will be preceeded by a seek to the end of file. Some platforms will seek and write atomically, others will not.

FileChannels has a virtual pointer into the file which is refered to as a file position. The position can be manipulated by repositioning it within the file, and its current position can be queried.

FileChannels also have an associated size. The size of the file is the number of bytes that it currently contains. The size can be manipulated by adding more bytes to the end of the file (which increases the size) or truncating the file (which decreases the size). The current size can also be queried.

FileChannels have operations beyond the simple read, write, and close. They can also:
- request that cached data be forced onto the disk
- lock ranges of bytes associated with the file
- transfer data directly to another channel in a manner that has the potential to be optimized by the platform
- memory-mapping files into NIO buffers to provide efficient manipulation of file data
- read and write to the file at absolute byte offsets in a fashion that does not modify the current position
FileChannels are thread-safe. Only one operation involving manipulation of the file position may be in-flight at once. Subsequent calls to such operations will block, and one of those blocked will be freed to continue when the first operation has completed. There is no ordered queue or fairness applied to the blocked threads.

It is undefined whether operations that do not manipulate the file position will also block when there are any other operations in-flight.

The logical view of the underlying file is consistent across all FileChannels and IO streams opened on the same file by the same JVM process. Therefore modifications performed via a channel will be visible to the stream, and vice versa; including modifications to the file position, content, size, etc.

            FileLock lock = null;
            boolean writable;


            try {
                fos = new FileOutputStream(file, true);
                FileChannel channel = fos.getChannel();
                lock = channel.tryLock();
            } catch (IOException e) {
                log.warn("Error while attempting to lock the file: " + file.getName(), e);
                writable = false;
            } finally {
                if (lock != null) {

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    }


    public static void handleResponse(final ReadRequestMessage request, final ProtocolEncoderOutput out, final ConcurrentMap<String, FileChannel> fdCacheMap) {
        final String filePath = request.filePath;


        FileChannel fileChannel = fdCacheMap.get(filePath);
        if(fileChannel == null) {
            File file = new File(filePath);
            if(!file.exists()) {
                throw new IllegalStateException("file not exists: " + filePath);
            }

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        } catch (IOException e) {
            LOG.error(e);
            throw e;
        }


        FileChannel fileChannel = fdCacheMap.get(filePath);
        if(fileChannel == null) {
            if(!dataFile.exists()) {
                throw new IllegalStateException("file not exists: " + filePath);
            }
            final RandomAccessFile raf;
            try {
                raf = new RandomAccessFile(dataFile, "r");
            } catch (FileNotFoundException e) {
                throw new IllegalStateException(e);
            }
            fileChannel = raf.getChannel();
            fdCacheMap.put(filePath, fileChannel);
        }


        for(int i = 0; i < size; i++) {
            final long offset = offsets[i];
            // get data length
            final ByteBuffer tmpBuf = ByteBuffer.allocate(4);
            try {
                fileChannel.read(tmpBuf, offset);
            } catch (IOException e) {
                LOG.error(e);
                throw e;
            }
            tmpBuf.flip();

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      throw new RuntimeException(e);
    }
  }


  private static ByteBuffer readFile(final File file) throws IOException {
    final FileChannel channel = new FileInputStream(file).getChannel();


    final long bytesTotal = channel.size();
    final ByteBuffer buffer = ByteBuffer.allocateDirect((int)bytesTotal);


    long bytesRead = 0;
    do {
      bytesRead += channel.read(buffer);
    } while ( bytesRead < bytesTotal );
    buffer.flip();


    channel.close();


    return buffer;
  }

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  }
  


  private MappedByteBuffer createMappedBuffer( long file_offset, int length ) throws IOException {
    if ( channel == null ) {
      FileChannel fc = new RandomAccessFile( file, "rw" ).getChannel();
      MappedByteBuffer mbb = fc.map( FileChannel.MapMode.READ_WRITE, file_offset, length );
      if ( access_mode == MODE_READ_ONLY ) fc.close();
      else channel = fc;
      return mbb;
    }
    
    return channel.map( FileChannel.MapMode.READ_WRITE, file_offset, length );

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    if (raf == null){
      
      throw new FMFileManagerException( "read: raf is null" );
    }
    
    FileChannel fc = raf.getChannel();
        
    if ( !fc.isOpen()){
      
      Debug.out("FileChannel is closed: " + owner.getName());
      
      throw( new FMFileManagerException( "read - file is closed"));
    }


    AEThread2.setDebug( owner );
    
    try{
      if(USE_MMAP)
      {
        long remainingInFile = fc.size()-offset;
        long remainingInTargetBuffer = buffer.remaining(DirectByteBuffer.SS_FILE);
        MappedByteBuffer buf = fc.map(MapMode.READ_ONLY, offset, Math.min(remainingInFile,remainingInTargetBuffer));
        buffer.put(DirectByteBuffer.SS_FILE, buf);
      } else {
        fc.position(offset);
        while (fc.position() < fc.size() && buffer.hasRemaining(DirectByteBuffer.SS_FILE))
          buffer.read(DirectByteBuffer.SS_FILE,fc);        
      }

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    if ( raf == null ){
      
      throw new FMFileManagerException( "read: raf is null" );
    }
    
    FileChannel fc = raf.getChannel();
        
    if ( !fc.isOpen()){
      
      Debug.out("FileChannel is closed: " + owner.getName());
      
      throw( new FMFileManagerException( "read - file is closed"));
    }
    
    AEThread2.setDebug( owner );
    
    int[]  original_positions = new int[buffers.length];
    
    long read_start = SystemTime.getHighPrecisionCounter();
    
    try{
      if(USE_MMAP)
      {
        
        long size = 0;
        for(int i=0;i<buffers.length;i++)
        {
          size += buffers[i].remaining(DirectByteBuffer.SS_FILE);
          original_positions[i] = buffers[i].position(DirectByteBuffer.SS_FILE);
        }
          
        size = Math.min(size, fc.size()-offset);
        MappedByteBuffer buf = fc.map(MapMode.READ_ONLY, offset, size);
        for(DirectByteBuffer b : buffers)
        {
          buf.limit(buf.position()+b.remaining(DirectByteBuffer.SS_FILE));
          b.put(DirectByteBuffer.SS_FILE, buf);
        }
          
        
      } else {
        
        fc.position(offset);
        ByteBuffer[]  bbs = new ByteBuffer[buffers.length];
        
        ByteBuffer  last_bb  = null;
        for (int i=0;i<bbs.length;i++){
          ByteBuffer bb = bbs[i] = buffers[i].getBuffer(DirectByteBuffer.SS_FILE);
          int  pos = original_positions[i] = bb.position();
          if ( pos != bb.limit()){
            last_bb  = bbs[i];
          }
        }
        
        if ( last_bb != null ){
          int    loop      = 0;
          
            // we sometimes read off the end of the file (when rechecking) so
            // bail out if we've completed the read or got to file end
            // a "better" fix would be to prevent the over-read in the first
            // place, but hey, we're just about to release and there may be other
            // instances of this...


          while ( fc.position() < fc.size() && last_bb.hasRemaining()){
            long  read = fc.read( bbs );
            if ( read > 0 ){
              loop  = 0;
            }else{
              loop++;
              if ( loop == READ_RETRY_LIMIT ){

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  {
    if ( raf == null){
      throw( new FMFileManagerException( "write fails: raf is null" ));
    }
    
    FileChannel fc = raf.getChannel();
    
    if ( !fc.isOpen()){
      
      Debug.out("FileChannel is closed: " + owner.getName());
      
      throw( new FMFileManagerException( "read - file is closed"));
    }


    AEThread2.setDebug( owner );
    
    int[]  original_positions = new int[buffers.length];


    try{
      
      if(USE_MMAP) {
        long size = 0;
        for(int i=0;i<buffers.length;i++)
        {
          size += buffers[i].remaining(DirectByteBuffer.SS_FILE);
          original_positions[i] = buffers[i].position(DirectByteBuffer.SS_FILE);
        }
        
        if(position+size > fc.size())
        {
          fc.position(position+size-1);
          fc.write(ByteBuffer.allocate(1));
          fc.force(true);
        }
          
        MappedByteBuffer buf = fc.map(MapMode.READ_WRITE, position, size);
        for(DirectByteBuffer b : buffers)
          buf.put(b.getBuffer(DirectByteBuffer.SS_FILE));
        buf.force();
      } else {
        long  expected_write   = 0;
        long  actual_write  = 0;
        boolean  partial_write  = false;
        
        if ( DEBUG ){
          for (int i=0;i<buffers.length;i++){
            expected_write += buffers[i].limit(DirectByteBuffer.SS_FILE) - buffers[i].position(DirectByteBuffer.SS_FILE);
          }
        }
        
        fc.position( position );
        ByteBuffer[]  bbs = new ByteBuffer[buffers.length];




        ByteBuffer  last_bb  = null;
        for (int i=0;i<bbs.length;i++){
          ByteBuffer bb = bbs[i] = buffers[i].getBuffer(DirectByteBuffer.SS_FILE);
          int  pos = original_positions[i] = bb.position();
          if ( pos != bb.limit()){
            last_bb  = bbs[i];
          }
        }
        
        if ( last_bb != null ){
          int loop = 0;
          
          while( last_bb.position() != last_bb.limit()){
            long written = fc.write( bbs );
            actual_write += written;
            
            if ( written > 0 ){
              loop  = 0;
              if ( DEBUG ){

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                RandomAccessFile raf = null;
                PDFFile pdffile;
                try {
                    
                    raf = new RandomAccessFile(file, "r");
                    FileChannel channel = raf.getChannel();
                    ByteBuffer buf = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
                    pdffile = new PDFFile(buf);
                    pdffile.stop(1);
    
                    try {
                        book.setValue(Book._T_NROFPAGES, Long.valueOf(pdffile.getNumPages()));

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    //File fileXML = new File("/users/epsobolik/documents/SchbAvMaSample.xml");
    try {
        FileInputStream fisXML = new FileInputStream(fileXML);
        
        //  test the XML file by displaying the first 1024 characters
      FileChannel fc = fisXML.getChannel();
      ByteBuffer buf = ByteBuffer.allocate((int)fc.size());
      fc.read(buf);
      buf.flip();
  //      while(buf.hasRemaining())
  //        System.out.print((char)buf.get());
  //      fisXML.close();
  //      System.out.print('\n');

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