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




        FileChannel inChannel = inRandom.getChannel();


        //将输入文件的通道通过只读的权限 映射到内存中。
        MappedByteBuffer byteMapper = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, (int) inFile.length());


        CharsetDecoder inDecoder = inCharset.newDecoder();
        CharsetEncoder outEncoder = outCharset.newEncoder();


        CharBuffer cb = inDecoder.decode(byteMapper);

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                            || (start > 0 && start <= logFileTime && end > 0 && end >= logFileTime)) {


                        // It's in the range, so process the file
                        RandomAccessFile raf = new RandomAccessFile(logFile, "r");
                        FileChannel fc = raf.getChannel();
                        MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
                        CharBuffer cb = Charset.forName("US-ASCII").decode(bb); //todo: does Jetty use a different charset on a foreign PC?
                        Matcher lines = FULL_LINE_PATTERN.matcher(cb);
                        Matcher target = ACCESS_LOG_PATTERN.matcher("");
                        SimpleDateFormat format = (start == 0 && end == 0) ? null : new SimpleDateFormat(ACCESS_LOG_DATE_FORMAT);
                        int max = maxResults == null ? MAX_SEARCH_RESULTS : Math.min(maxResults.intValue(), MAX_SEARCH_RESULTS);

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    static public String read(String path) throws MinException {
        try {
            FileInputStream stream = new FileInputStream(new java.io.File(path));
            try {
                FileChannel fc = stream.getChannel();
                MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
        /* Instead of using default, pass in a decoder. */
                return java.nio.charset.Charset.defaultCharset().decode(bb).toString();
            } finally {
                stream.close();
            }

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        boolean capped = false;
        int lineCount = 0;
        try {
            RandomAccessFile raf = new RandomAccessFile(file, "r");
            FileChannel fc = raf.getChannel();
            MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
            CharBuffer cb = Charset.forName("US-ASCII").decode(bb); //todo: does Jetty use a different charset on a foreign PC?
            Matcher lines = FULL_LINE_PATTERN.matcher(cb);
            Matcher target = ACCESS_LOG_PATTERN.matcher("");
            long start = startDate == null ? 0 : startDate.getTime();
            long end = endDate == null ? 0 : endDate.getTime();

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        boolean capped = false;
        int lineCount = 0;
        try {
            RandomAccessFile raf = new RandomAccessFile(file, "r");
            FileChannel fc = raf.getChannel();
            MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
            CharBuffer cb = Charset.forName("US-ASCII").decode(bb); //todo: does Log4J use a different charset on a foreign PC?
            Matcher target = null;
            Matcher any = null;
            Matcher lines = FULL_LINE_PATTERN.matcher(cb);
            Matcher text = textSearch == null ? null : textSearch.matcher("");

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        boolean capped = false;
        int lineCount = 0;
        try {
            RandomAccessFile raf = new RandomAccessFile(file, "r");
            FileChannel fc = raf.getChannel();
            MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
            CharBuffer cb = Charset.forName("US-ASCII").decode(bb); //todo: does Log4J use a different charset on a foreign PC?
            Matcher target = null;
            Matcher any = null;
            Matcher lines = FULL_LINE_PATTERN.matcher(cb);
            Matcher text = textSearch == null ? null : textSearch.matcher("");

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   * OS pages into this process's page. It will be automatically unmapped when
   * the ByteBuffer that is returned here goes out of scope. This method is
   * currently invoked only by the FSDataInputStream ScatterGather api.
   */
  public ByteBuffer readAll() throws IOException {
    MappedByteBuffer bb = dataIn.getChannel().map(FileChannel.MapMode.READ_ONLY,
                                 startOffset, length);
    return bb;  
  }

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               {
                  chf = File.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
                  // TODO don't use Channels.newChannel in Java5
                  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();
                     chf.delete();
                  }
                  catch (Exception e1)
                  {
                  }
                  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();
                     chf.delete();
                  }
                  catch (Exception e1)
                  {
                  }
                  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 (!spoolFile.delete())
            {
               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. "
                     + spoolFile.getAbsolutePath());
               }
            }


            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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               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); // TODO don't use Channels.newChannel on java5
            ch.write(bb);
            ch.close();

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