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

     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_ReadOnly_CloseChannel() throws IOException {
        // close channel has no effect on map if mapped
        assertEquals(0, readWriteFileChannel.size());
        MappedByteBuffer mapped = readWriteFileChannel.map(MapMode.READ_ONLY,
                0, CONTENT_LENGTH);
        assertEquals(CONTENT_LENGTH, readWriteFileChannel.size());
        readOnlyFileChannel.close();
        assertEquals(CONTENT_LENGTH, mapped.limit());
    }

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    /**
     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_Private_CloseChannel() throws IOException {
        MappedByteBuffer mapped = readWriteFileChannel.map(MapMode.PRIVATE, 0,
                CONTENT_LENGTH);
        readWriteFileChannel.close();
        mapped.put(TEST_BYTES);
        assertEquals(CONTENT_LENGTH, mapped.limit());
        assertEquals("test".length(), mapped.position());
    }

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    /**
     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_ReadOnly() throws IOException {
        MappedByteBuffer mapped = null;
        // try put something to readonly map
        writeDataToFile(fileOfReadOnlyFileChannel);
        mapped = readOnlyFileChannel.map(MapMode.READ_ONLY, 0, CONTENT_LENGTH);
        try {
            mapped.put(TEST_BYTES);
            fail("should throw ReadOnlyBufferException.");
        } catch (ReadOnlyBufferException ex) {
            // expected;
        }
        assertEquals(CONTENT_LENGTH, mapped.limit());
        assertEquals(CONTENT_LENGTH, mapped.capacity());
        assertEquals(0, mapped.position());


        // try to get a readonly map from read/write channel
        writeDataToFile(fileOfReadWriteFileChannel);
        mapped = readWriteFileChannel.map(MapMode.READ_ONLY, 0, CONTENT
                .length());
        assertEquals(CONTENT_LENGTH, mapped.limit());
        assertEquals(CONTENT_LENGTH, mapped.capacity());
        assertEquals(0, mapped.position());


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

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    /**
     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_ReadOnly_NonZeroPosition() throws IOException {
        this.writeDataToFile(fileOfReadOnlyFileChannel);
        MappedByteBuffer mapped = readOnlyFileChannel.map(MapMode.READ_ONLY,
                10, CONTENT_LENGTH - 10);
        assertEquals(CONTENT_LENGTH - 10, mapped.limit());
        assertEquals(CONTENT_LENGTH - 10, mapped.capacity());
        assertEquals(0, mapped.position());
    }

View Full Code Here

    /**
     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_Private() throws IOException {
        this.writeDataToFile(fileOfReadWriteFileChannel);
        MappedByteBuffer mapped = readWriteFileChannel.map(MapMode.PRIVATE, 0,
                CONTENT_LENGTH);
        assertEquals(CONTENT_LENGTH, mapped.limit());
        // test copy on write if private
        ByteBuffer returnByPut = mapped.put(TEST_BYTES);
        assertSame(returnByPut, mapped);
        ByteBuffer checkBuffer = ByteBuffer.allocate(CONTENT_LENGTH);
        mapped.force();
        readWriteFileChannel.read(checkBuffer);
        assertEquals(CONTENT, new String(checkBuffer.array(), "iso8859-1"));


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

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        }
        long alignment = position - position % ALLOC_GRANULARITY;
        int offset = (int) (position - alignment);
        PlatformAddress address = PlatformAddressFactory.allocMap(handle,
                alignment, size + offset, mapMode);
        MappedByteBuffer buffer = null;
        try {
            buffer = MappedByteBufferFactory.getBuffer(address, mapMode, size,
                    offset);
        } catch (Exception e) {
            throw new IOException(e.getMessage());

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     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_ReadOnly_CloseChannel() throws IOException {
        // close channel has no effect on map if mapped
        assertEquals(0, readWriteFileChannel.size());
        MappedByteBuffer mapped = readWriteFileChannel.map(MapMode.READ_ONLY,
                0, CONTENT_LENGTH);
        assertEquals(CONTENT_LENGTH, readWriteFileChannel.size());
        readOnlyFileChannel.close();
        assertEquals(CONTENT_LENGTH, mapped.limit());
    }

View Full Code Here


    /**
     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_Private_CloseChannel() throws IOException {
        MappedByteBuffer mapped = readWriteFileChannel.map(MapMode.PRIVATE, 0,
                CONTENT_LENGTH);
        readWriteFileChannel.close();
        mapped.put(TEST_BYTES);
        assertEquals(CONTENT_LENGTH, mapped.limit());
        assertEquals("test".length(), mapped.position());
    }

View Full Code Here


    /**
     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_ReadOnly() throws IOException {
        MappedByteBuffer mapped = null;
        // try put something to readonly map
        writeDataToFile(fileOfReadOnlyFileChannel);
        mapped = readOnlyFileChannel.map(MapMode.READ_ONLY, 0, CONTENT_LENGTH);
        try {
            mapped.put(TEST_BYTES);
            fail("should throw ReadOnlyBufferException.");
        } catch (ReadOnlyBufferException ex) {
            // expected;
        }
        assertEquals(CONTENT_LENGTH, mapped.limit());
        assertEquals(CONTENT_LENGTH, mapped.capacity());
        assertEquals(0, mapped.position());


        // try to get a readonly map from read/write channel
        writeDataToFile(fileOfReadWriteFileChannel);
        mapped = readWriteFileChannel.map(MapMode.READ_ONLY, 0, CONTENT
                .length());
        assertEquals(CONTENT_LENGTH, mapped.limit());
        assertEquals(CONTENT_LENGTH, mapped.capacity());
        assertEquals(0, mapped.position());


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

View Full Code Here

    /**
     * @tests java.nio.channels.FileChannel#map(MapMode,long,long)
     */
    public void test_map_ReadOnly_NonZeroPosition() throws IOException {
        this.writeDataToFile(fileOfReadOnlyFileChannel);
        MappedByteBuffer mapped = readOnlyFileChannel.map(MapMode.READ_ONLY,
                10, CONTENT_LENGTH - 10);
        assertEquals(CONTENT_LENGTH - 10, mapped.limit());
        assertEquals(CONTENT_LENGTH - 10, mapped.capacity());
        assertEquals(0, mapped.position());
    }

View Full Code Here

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