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

  private byte[] mapFileIn(File infile) throws IOException{
    FileInputStream fis = new FileInputStream(infile);
    try{
      FileChannel fc = fis.getChannel(); // Get the file's size and then map it into memory
      int sz = (int)fc.size();
      MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, sz);
      byte[] data2 = new byte[bb.remaining()];
      bb.get(data2);
      return data2;
    }
    finally{//Ensures resources are closed regardless of whether the action suceeded
      fis.close();
    }

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      if (position + length >= channel.size())
      {
         length = channel.size() - position;
      }


      MappedByteBuffer bb = channel.map(FileChannel.MapMode.READ_ONLY, position, length);


      WritableByteChannel ch;
      if (stream instanceof FileOutputStream)
      {
         ch = ((FileOutputStream)stream).getChannel();

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               throw new IOException("Position " + position + " out of value size " + spoolChannel.size());


            if (position + length >= spoolChannel.size())
               length = spoolChannel.size() - position;


            MappedByteBuffer bb = spoolChannel.map(FileChannel.MapMode.READ_ONLY, position, length);


            WritableByteChannel ch = Channels.newChannel(stream);
            ch.write(bb);
            ch.close();

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               {
                  chf = SpoolFile.createTempFile("jcrvdedit", null, tempDirectory);
                  chch = new RandomAccessFile(chf, "rw").getChannel();


                  // allocate the space for whole file
                  MappedByteBuffer bb = chch.map(FileChannel.MapMode.READ_WRITE, position + length, 0);
                  bb.force();
                  bb = null;


                  ReadableByteChannel bch = Channels.newChannel(new ByteArrayInputStream(this.data));


                  if ((newIndex = (int)position) > 0)
                  {
                     // begin from the existed bytes
                     chch.transferFrom(bch, 0, newIndex < data.length ? newIndex : data.length);
                     bch.close();
                  }


                  // write update data
                  ReadableByteChannel sch = Channels.newChannel(stream);
                  chch.transferFrom(sch, newIndex, length);
                  sch.close();
                  newIndex += length;


                  if (newIndex < data.length)
                     // write the rest of existed data
                     chch.transferFrom(bch, newIndex, data.length - newIndex);


                  bch.close();
               }
               catch (final IOException e)
               {
                  try
                  {
                     chch.close();
                     PrivilegedFileHelper.delete(chf);
                  }
                  catch (Exception e1)
                  {
                     if (LOG.isTraceEnabled())
                     {
                        LOG.trace("An exception occurred: " + e1.getMessage());
                     }
                  }
                  throw new IOException("update error " + e.getMessage())
                  {
                     @Override
                     public Throwable getCause()
                     {
                        return e;
                     }
                  };
               }
               this.spoolFile = chf;
               this.spoolChannel = chch;
               this.data = null;
            }
         }
         else
         {
            MappedByteBuffer bb = spoolChannel.map(FileChannel.MapMode.READ_WRITE, position, length);


            ReadableByteChannel ch = Channels.newChannel(stream);
            ch.read(bb);
            ch.close();


            bb.force();
         }
      }

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                  bch.close();


                  if (chch.size() < size)
                  {
                     // extend length
                     MappedByteBuffer bb = chch.map(FileChannel.MapMode.READ_WRITE, size, 0);
                     bb.force();
                  }
               }
               catch (final IOException e)
               {
                  try
                  {
                     chch.close();
                     PrivilegedFileHelper.delete(chf);
                  }
                  catch (Exception e1)
                  {
                     if (LOG.isTraceEnabled())
                     {
                        LOG.trace("An exception occurred: " + e1.getMessage());
                     }
                  }
                  throw new IOException("setLength(" + size + ") error. " + e.getMessage())
                  {
                     @Override
                     public Throwable getCause()
                     {
                        return e;
                     }
                  };
               }
               this.spoolFile = chf;
               this.spoolChannel = chch;
               this.data = null;
            }
         }
         else if (size < maxBufferSize)
         {
            // switch to bytes
            ByteBuffer bb = ByteBuffer.allocate((int)size);
            spoolChannel.force(false);
            spoolChannel.position(0);
            spoolChannel.read(bb);


            byte[] tmpb = null;


            if (bb.hasArray())
            {
               tmpb = bb.array();
            }
            else
            {
               // impossible code in most cases, as we use heap backed buffer
               tmpb = new byte[bb.capacity()];
               bb.get(tmpb);
            }


            spoolChannel.close();


            // delete file
            if (!PrivilegedFileHelper.delete(spoolFile))
            {
               if (fileCleaner != null)
               {
                  LOG.info("Could not remove file. Add to fileCleaner " + spoolFile);
                  fileCleaner.addFile(spoolFile);
               }
               else
               {
                  LOG.warn("Could not remove temporary file on switch to bytes, fileCleaner not found. "
                     + PrivilegedFileHelper.getAbsolutePath(spoolFile));
               }
            }


            data = tmpb;
            spoolChannel = null;
            spoolFile = null;
         }
         else
         {
            if (spoolChannel.size() < size)
            {
               // extend file
               MappedByteBuffer bb = spoolChannel.map(FileChannel.MapMode.READ_WRITE, size, 0);
               bb.force();
            }
            else
            {
               // truncate file
               spoolChannel.truncate(size);

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    short numberOfSections;
    /* A pointer to the "optional" header (which will always be present in .exe files */
    int ptrOptionalHeader;


    /* The file we're reading from.*/
    MappedByteBuffer file = new FileInputStream(filename).getChannel().map(FileChannel.MapMode.READ_ONLY, 0, new File(filename).length());
    /* Set the file ordering to little endian */
    file.order(ByteOrder.LITTLE_ENDIAN);


    /* The start of the PE is pointed at by the 0x3c'th byte */
    peStart = file.getInt(PE_START);


    /* The first 4 bytes are the signature */
    peSignature = file.getInt(peStart + 0);


    /* Verify that it's a valid pe file.  IF not, throw an exception */
    if(peSignature != 0x00004550)
      throw new IOException("Invalid PE file!");


    /* The number of sections is the short starting at the 6th byte */
    numberOfSections = file.getShort(peStart + 6);


    /* Get a pointer to the optional header */
    ptrOptionalHeader = peStart + 24;

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    /**
     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_Private_NonZeroPosition() throws IOException {
        MappedByteBuffer mapped = readWriteFileChannel.map(MapMode.PRIVATE, 10,
                CONTENT_LENGTH - 10);
        assertEquals(CONTENT_LENGTH - 10, mapped.limit());
        assertEquals(CONTENT_LENGTH - 10, mapped.capacity());
        assertEquals(0, mapped.position());
    }

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    /**
     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_ReadWrite() throws IOException {
        MappedByteBuffer mapped = null;
        writeDataToFile(fileOfReadWriteFileChannel);
        mapped = readWriteFileChannel.map(MapMode.READ_WRITE, 0, CONTENT
                .length());


        // put something will change its channel
        ByteBuffer returnByPut = mapped.put(TEST_BYTES);
        assertSame(returnByPut, mapped);
        String checkString = "test" + CONTENT.substring(4);
        ByteBuffer checkBuffer = ByteBuffer.allocate(CONTENT_LENGTH);
        mapped.force();
        readWriteFileChannel.position(0);
        readWriteFileChannel.read(checkBuffer);
        assertEquals(checkString, new String(checkBuffer.array(), "iso8859-1"));


        try {
            mapped.put(("test" + CONTENT).getBytes("iso8859-1"));
            fail("should throw BufferOverflowException.");
        } catch (BufferOverflowException ex) {
            // expected;
        }
    }

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     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_ReadWrite_NonZeroPosition() throws IOException {
        // test position non-zero
        writeDataToFile(fileOfReadWriteFileChannel);
        MappedByteBuffer mapped = readWriteFileChannel.map(MapMode.READ_WRITE,
                10, CONTENT_LENGTH - 10);
        assertEquals(CONTENT_LENGTH - 10, mapped.limit());
        assertEquals(CONTENT.length() - 10, mapped.capacity());
        assertEquals(0, mapped.position());
        mapped.put(TEST_BYTES);
        ByteBuffer checkBuffer = ByteBuffer.allocate(CONTENT_LENGTH);
        readWriteFileChannel.read(checkBuffer);
        String expected = CONTENT.substring(0, 10) + "test"
                + CONTENT.substring(10 + "test".length());
        assertEquals(expected, new String(checkBuffer.array(), "iso8859-1"));

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                readOnlyFileChannel = new FileInputStream(fileOfReadOnlyFileChannel)
                        .getChannel();
            }


            writeLargeDataToFile(fileOfReadOnlyFileChannel, sizes[i] + 2 * CONTENT_LEN);
            MappedByteBuffer mapped = readOnlyFileChannel.map(MapMode.READ_ONLY,
                    sizes[i], CONTENT_LEN);
            assertEquals("Incorrectly mapped file channel for " + sizes[i]
                    + " position (capacity)", CONTENT_LEN, mapped.capacity());
            assertEquals("Incorrectly mapped file channel for " + sizes[i]
                    + " position (limit)", CONTENT_LEN, mapped.limit());
            assertEquals("Incorrectly mapped file channel for " + sizes[i]
                    + " position (position)", 0, mapped.position());


            // map not change channel's position
            assertEquals(0, readOnlyFileChannel.position());


            // Close the file and the channel before the next iteration

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