java nio file 内存映射文件

原理：内存映射文件原理探索

java对象解析：java内存映射文件

java对象中，介绍是用普通的bytebuffer来做的，而我们在实际生产环境中使用MappedByteBuffer。

介绍中是操作FileChannel的write、force、close等方法。使用MappedByteBuffer = FileChannel.map(..)产生，只要操作MappedByteBuffer的put、force方法就好了

MappedByteBuffer代码：

package file.ram.map;import sun.misc.Cleaner;import sun.nio.ch.DirectBuffer;import sun.nio.ch.FileChannelImpl;import java.io.File;import java.io.IOException;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.nio.MappedByteBuffer;import java.nio.channels.FileChannel;import java.nio.charset.StandardCharsets;import java.nio.file.Files;import java.nio.file.StandardCopyOption;import java.nio.file.StandardOpenOption;import java.util.concurrent.atomic.AtomicInteger;public class FileMMap {    private static AtomicInteger pos = new AtomicInteger();    private static FileChannel channel;    private static MappedByteBuffer mmap;    private static long size = 1024L;    public static void main(String[] args) throws IOException, InterruptedException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {        File file = new File("./test.dump");        channel = FileChannel.open(file.toPath(), StandardOpenOption.CREATE,                StandardOpenOption.READ, StandardOpenOption.WRITE);        mmap = channel.map(FileChannel.MapMode.READ_WRITE, 0, size);        byte[] len = new byte[8];        mmap.get(len);        System.out.println(mmap.capacity());        System.out.println(mmap.limit());        System.out.println(mmap.remaining());        mmap.put("abc".getBytes(StandardCharsets.UTF_8));        // channel.close();        // System.out.println(mmap.slice());        for (int i = 0; i < 10000; i++) {//            channel.transferTo(0, channel.size(), FileChannel.open(new File("./test1.dump").toPath(),//                    StandardOpenOption.CREATE, StandardOpenOption.WRITE));            // 移动            Files.move(file.toPath(), new File("./test1.dump").toPath(),                    StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.ATOMIC_MOVE);            channel.close();            // 新建            channel = FileChannel.open(file.toPath(), StandardOpenOption.CREATE,                    StandardOpenOption.READ, StandardOpenOption.WRITE);            // 手动unmap//            Method m = FileChannelImpl.class.getDeclaredMethod("unmap",//                    MappedByteBuffer.class);//            m.setAccessible(true);//            m.invoke(FileChannelImpl.class, mmap);            // 可以直接释放MappedByteBuffer            Cleaner var1 = ((DirectBuffer)mmap).cleaner();            if(var1 != null) {                var1.clean();            }            mmap = channel.map(FileChannel.MapMode.READ_WRITE, 0, size);            mmap.put(String.valueOf(i + 1).getBytes(StandardCharsets.UTF_8));        }    }}