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 boolean compareFiles(File f1, File f2) throws Exception {
        RandomAccessFile i1 = new RandomAccessFile(f1, "r");
        try {
            RandomAccessFile i2 = new RandomAccessFile(f2, "r");
            try {
                final MappedByteBuffer m1 = i1.getChannel().map(MapMode.READ_ONLY, 0, i1.length());
                final MappedByteBuffer m2 = i2.getChannel().map(MapMode.READ_ONLY, 0, i2.length());
                while (m1.hasRemaining() && m2.hasRemaining()) {
                    final byte b1 = m1.get();
                    final byte b2 = m2.get();
                    if (b1 != b2)
                        return false;


                }
                if (m1.hasRemaining() || m2.hasRemaining())
                    return false;
            } finally {
                i2.close();
            }
        } finally {

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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(System.getProperty("file.encoding")).decode(bb);
            Matcher target = null;
            Matcher any = null;
            Matcher lines = FULL_LINE_PATTERN.matcher(cb);
            Matcher text = textSearch == null ? null : textSearch.matcher("");

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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(logFiles[i], "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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                       || (start>0 && start<=logFileTime && end>0 && end>=logFileTime)) {


                        // It's in the range, so process the file
                        RandomAccessFile raf = new RandomAccessFile(logFiles[i], "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 Tomcat 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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        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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            assert file.exists() : file;
            // memory mapped file
            FileInputStream input = new FileInputStream(file);
            FileChannel channel = input.getChannel();
            long fileLength = channel.size();
            MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, fileLength);
            // character buffer
            Charset charset = java.nio.charset.Charset.forName("UTF-8");
            CharsetDecoder decoder = charset.newDecoder();
            return decoder.decode(buffer);
        } catch (Exception ex) {

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            assert file.exists() : file;
            // memory mapped file
            FileInputStream input = new FileInputStream(file);
            FileChannel channel = input.getChannel();
            long fileLength = channel.size();
            MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, fileLength);
            // character buffer
            Charset charset = java.nio.charset.Charset.forName("UTF-8");
            CharsetDecoder decoder = charset.newDecoder();
            return decoder.decode(buffer);
        } catch (Exception ex) {

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  private String readFile(String path) throws IOException {
    FileInputStream stream = new FileInputStream(new 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 Charset.defaultCharset().decode(bb).toString();
    } finally {
      stream.close();

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    public static MappedByteBuffer getMap(@NotNull FileChannel fileChannel, long start, int size) throws IOException {
        for (int i = 1; ; i++) {
            try {
//                long startTime = System.nanoTime();
                @SuppressWarnings("UnnecessaryLocalVariable")
                MappedByteBuffer map = fileChannel.map(FileChannel.MapMode.READ_WRITE, start, size);
                map.order(ByteOrder.nativeOrder());
//                long time = System.nanoTime() - startTime;
//                System.out.printf("Took %,d us to map %,d MB%n", time / 1000, size / 1024 / 1024);
//                System.out.println("Map size: "+size);
                return map;
            } catch (IOException e) {

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        FileInputStream fis = new FileInputStream(f.getLocation().toFile());
        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);


        // Decode the file into a char buffer
        return decoder.decode(bb);
    }

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