java中使用mmap技术的实现示例

try (FileInputStream fis = new FileInputStream("file.txt")) {
    byte[] buffer = new byte[8192]; // 8KB 缓冲区
    int bytesRead;
    while ((bytesRead = fis.read(buffer)) != -1) {
        // 处理 buffer 中的前 bytesRead 字节
    }
}

try (FileChannel channel = FileChannel.open(Paths.get("data.txt"), StandardOpenOption.READ)) {
    MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, size);
}

AsynchronousFileChannel

try (var arena = Arena.ofConfined();
     var channel = FileChannel.open(path, StandardOpenOption.READ)) {
    var size = channel.size();
    var memorySegment = channel.map(FileChannel.MapMode.READ_ONLY,
            0,
            size,
            arena
    );

} catch (IOException e) {
    throw new RuntimeException(e);
}

public class MemorySegmentFileTest {
    private static final Path path = Path.of("/home/bin-/Downloads/home/extraData.img");

    static void main() {
        try (var arena = Arena.ofConfined();
             var channel = FileChannel.open(path, StandardOpenOption.READ)) {
            var size = channel.size();
            var memorySegment = channel.map(FileChannel.MapMode.READ_ONLY,
                    0,
                    size,
                    arena
            );

            System.out.println("成功映射文件，大小：" + printSize(size));
            System.out.println("内存段地址：" + memorySegment.address());
            System.out.println("内存段大小：" + printSize(memorySegment.byteSize()));
            System.out.println("内存段内容前16字节：");
            for (long i = 0; i < 16; i++) {
                byte b = memorySegment.get(ValueLayout.JAVA_BYTE, i);
                System.out.printf("0x%02X ", b);
            }
            System.out.println();
            System.out.println("内存段内容后16字节：");
            for (long i = size - 16; i < size; i++) {
                byte b = memorySegment.get(ValueLayout.JAVA_BYTE, i);
                System.out.printf("0x%02X ", b);
            }
            System.out.println();

        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    private static String printSize(long size) {
        String[] units = {"B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB"};
        long s = size;
        var list = new ArrayList<String>();
        var builder = new StringBuilder();
        var formatter = new Formatter(builder);
        for (var unit : units) {
            int sub = (int) (s & ((1 << 10) - 1));
            formatter.format("%s %s", sub, unit);
            list.add(builder.toString());
            builder.setLength(0);
            if (s < 1024) {
                break;
            }
            s >>= 10;
        }
        return String.join(" ", list.reversed());
    }
}