Examples of java.nio.MappedByteBuffer

java.nio.MappedByteBuffer
A direct byte buffer whose content is a memory-mapped region of a file.
Mapped byte buffers are created via the {@link java.nio.channels.FileChannel#map FileChannel.map} method. This classextends the {@link ByteBuffer} class with operations that are specific tomemory-mapped file regions.
A mapped byte buffer and the file mapping that it represents remain valid until the buffer itself is garbage-collected.
The content of a mapped byte buffer can change at any time, for example if the content of the corresponding region of the mapped file is changed by this program or another. Whether or not such changes occur, and when they occur, is operating-system dependent and therefore unspecified.
All or part of a mapped byte buffer may become inaccessible at any time, for example if the mapped file is truncated. An attempt to access an inaccessible region of a mapped byte buffer will not change the buffer's content and will cause an unspecified exception to be thrown either at the time of the access or at some later time. It is therefore strongly recommended that appropriate precautions be taken to avoid the manipulation of a mapped file by this program, or by a concurrently running program, except to read or write the file's content.
Mapped byte buffers otherwise behave no differently than ordinary direct byte buffers.
@author Mark Reinhold @author JSR-51 Expert Group @version 1.25, 09/02/26 @since 1.4

    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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          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 {

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          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;

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        final Map<MutableLongPair, CloseableMappedByteBuffer> pool = _pool;
        CloseableMappedByteBuffer buf;
        synchronized(pool) {
            buf = pool.get(pair);
            if(buf == null || !AtomicUtils.tryIncrementIfGreaterThan(buf.referenceCount(), 0)) {
                MappedByteBuffer bufimpl = map(pageOffset);
                buf = new CloseableMappedByteBuffer(bufimpl);
                pool.put(pair, buf);
            }
        }
        return buf;

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     */
    private MappedByteBuffer map(final long page) {
        if(_channel == null) {
            ensureOpen();
        }
        MappedByteBuffer buf;
        try {
            buf = _channel.map(_readOnly ? MapMode.READ_ONLY : MapMode.READ_WRITE, page, _pageSize);
        } catch (IOException e) {// silly workaround for JDK bug #4724038
            System.gc();
            System.runFinalization();
            try {
                buf = _channel.map(_readOnly ? MapMode.READ_ONLY : MapMode.READ_WRITE, page, _pageSize);
            } catch (IOException ioe) {
                throw new IllegalStateException("map failed for page#" + page + " of file: "
                        + _filepath, ioe);
            }
        }
        if(_setAsLittleEndian) {// BIG_ENDIAN by the default
            buf.order(ByteOrder.LITTLE_ENDIAN);
        }
        return buf;
    }

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      while (chFrom.charAt(start++)!=(char) 10) ;


      log.debug("  skip = " + String.valueOf(start));
      log.debug("  start = " + String.valueOf(begin+start));


      MappedByteBuffer byBuffer = getChannel().map(FileChannel.MapMode.READ_ONLY, begin+start, size);
      byte[] byArray = new byte[size];
      byBuffer.get(byArray);


      ByteArrayInputStream byStrm = new ByteArrayInputStream(byArray);


      return byStrm;
    }

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      start += offset;


      log.debug("  skip = " + String.valueOf(start));
      log.debug("  start = " + String.valueOf(start));


      MappedByteBuffer byBuffer = getChannel().map(FileChannel.MapMode.READ_ONLY, begin+start, size);
      byte[] byArray = new byte[size];
      byBuffer.get(byArray);


      ByteArrayInputStream byStrm = new ByteArrayInputStream(byArray);


      return byStrm;
    }

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      while (chFrom.charAt(start++)!=(char) 10) ;


      log.debug("  skip = " + String.valueOf(start));
      log.debug("  start = " + String.valueOf(position+start));


      MappedByteBuffer byBuffer = getChannel().map(FileChannel.MapMode.READ_ONLY, position+start, size-start);
      byte[] byArray = new byte[size-start];
      byBuffer.get(byArray);


      ByteArrayInputStream byStrm = new ByteArrayInputStream(byArray);


      return byStrm;
    }

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        try {
            in = new FileInputStream(source).getChannel();
            out = new FileOutputStream(dest).getChannel();


            long size = in.size();
            MappedByteBuffer buf = in.map(FileChannel.MapMode.READ_ONLY, 0, size);


            out.write(buf);


            if (in != null) {
                in.close();

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    RandomAccessFile raf =
        new RandomAccessFile(file, mode == MapMode.READ_ONLY ? "r" : "rw");


    boolean threw = true;
    try {
      MappedByteBuffer mbb = map(raf, mode, size);
      threw = false;
      return mbb;
    } finally {
      Closeables.close(raf, threw);
    }

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