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

        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 Derby use a different charset on a foreign PC?
            Matcher lines = FULL_LINE_PATTERN.matcher(cb);
            Matcher text = textSearch == null ? null : textSearch.matcher("");
            max = Math.min(max, MAX_SEARCH_RESULTS);
            while(lines.find()) {

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        FileInputStream fis = new FileInputStream(file);
        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);


        // Decode the file into a char buffer
        CharBuffer cb = decoder.decode(bb);


        // Perform the search

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        FileInputStream fis = new FileInputStream(file);
        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);


        // Decode the file into a char buffer
        CharBuffer cb = decoder.decode(bb);


        // Perform the search

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        FileInputStream fis = new FileInputStream(file);
        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);


  // Decode the file into a char buffer
        // Charset and decoder for ISO-8859-15
        Charset charset = Charset.forName("ISO-8859-15");
        CharsetDecoder decoder = charset.newDecoder();

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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 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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     */
    public void testasIntBuffer() throws IOException {
        // Map file
        FileInputStream fis = new FileInputStream(tmpFile);
        FileChannel fc = fis.getChannel();
        MappedByteBuffer mmb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc
                .size());
        int len = mmb.capacity();
        assertEquals("Got wrong number of bytes", 46, len); //$NON-NLS-1$


        // Read in our 26 bytes
        for (int i = 0; i < 26; i++) {
            byte b = mmb.get();
            assertEquals("Got wrong byte value", (byte) 'A' + i, b); //$NON-NLS-1$
        }


        // Now convert to an IntBuffer to read our ints
        IntBuffer ibuffer = mmb.asIntBuffer();
        for (int i = 0; i < 5; i++) {
            int val = ibuffer.get();
            assertEquals("Got wrong int value", i + 1, val); //$NON-NLS-1$
        }
        fc.close();

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     */
    public void testEmptyBuffer() throws IOException {
      // Map empty file
        FileInputStream fis = new FileInputStream(emptyFile);
        FileChannel fc = fis.getChannel();
        MappedByteBuffer mmb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
        
        // check non-null
        assertNotNull("MappedByteBuffer created from empty file should not be null", 
            mmb);
        
        // check capacity is 0
        int len = mmb.capacity();
        assertEquals("MappedByteBuffer created from empty file should have 0 capacity", 
            0, len);
        
        assertFalse("MappedByteBuffer from empty file shouldn't be backed by an array ", 
            mmb.hasArray());
        
        try
        {
          byte b = mmb.get();
          fail("Calling MappedByteBuffer.get() on empty buffer should throw a BufferUnderflowException");
        }
        catch (BufferUnderflowException e)
        {
          // expected behaviour

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     */
    public void test_force() throws IOException {
        // buffer was not mapped in read/write mode
        FileInputStream fileInputStream = new FileInputStream(tmpFile);
        FileChannel fileChannelRead = fileInputStream.getChannel();
        MappedByteBuffer mmbRead = fileChannelRead.map(MapMode.READ_ONLY, 0,
                fileChannelRead.size());


        mmbRead.force();


        FileInputStream inputStream = new FileInputStream(tmpFile);
        FileChannel fileChannelR = inputStream.getChannel();
        MappedByteBuffer resultRead = fileChannelR.map(MapMode.READ_ONLY, 0,
                fileChannelR.size());


        //If this buffer was not mapped in read/write mode, then invoking this method has no effect.
        assertEquals(
                "Invoking force() should have no effect when this buffer was not mapped in read/write mode",
                mmbRead, resultRead);


        // Buffer was mapped in read/write mode
        RandomAccessFile randomFile = new RandomAccessFile(tmpFile, "rw");
        FileChannel fileChannelReadWrite = randomFile.getChannel();
        MappedByteBuffer mmbReadWrite = fileChannelReadWrite.map(
                FileChannel.MapMode.READ_WRITE, 0, fileChannelReadWrite.size());


        mmbReadWrite.put((byte) 'o');
        mmbReadWrite.force();


        RandomAccessFile random = new RandomAccessFile(tmpFile, "rw");
        FileChannel fileChannelRW = random.getChannel();
        MappedByteBuffer resultReadWrite = fileChannelRW.map(
                FileChannel.MapMode.READ_WRITE, 0, fileChannelRW.size());


        // Invoking force() will change the buffer
        assertFalse(mmbReadWrite.equals(resultReadWrite));

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     * @tests {@link java.nio.MappedByteBuffer#load()}
     */
    public void test_load() throws IOException {
        FileInputStream fileInputStream = new FileInputStream(tmpFile);
        FileChannel fileChannelRead = fileInputStream.getChannel();
        MappedByteBuffer mmbRead = fileChannelRead.map(MapMode.READ_ONLY, 0,
                fileChannelRead.size());
        
        assertEquals(mmbRead, mmbRead.load());


        RandomAccessFile randomFile = new RandomAccessFile(tmpFile, "rw");
        FileChannel fileChannelReadWrite = randomFile.getChannel();
        MappedByteBuffer mmbReadWrite = fileChannelReadWrite.map(
                FileChannel.MapMode.READ_WRITE, 0, fileChannelReadWrite.size());


        assertEquals(mmbReadWrite, mmbReadWrite.load());
        
        fileChannelRead.close();
        fileChannelReadWrite.close();
    }

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