内存映射文件MappedByteBuffer和Buffer的Scattering与Gathering

上一篇讲到的DirectByteBuffer继承自MappedByteBuffer

一、MappedByteBuffer

MappedByteBuffer的定义：

A direct byte buffer whose content is a memory-mapped region of a file.

直接缓存，内容是一个内存映射文件。

创建测试类

public class NioTest9 {
    public static void main(String[] args) throws  Exception {
        RandomAccessFile randomAccessFile = new RandomAccessFile("NioTest9.txt","rw");
        FileChannel fileChannel =  randomAccessFile.getChannel();
        MappedByteBuffer mappedByteBuffer = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0,5);
        mappedByteBuffer.put(0,(byte)'a');
        mappedByteBuffer.put(3,(byte)'b');

        randomAccessFile.close();
    }
}

　创建NioTest9.tex文件

　运行程序，用记事本打开

操作的是堆外内存，堆外内存写入到文件由操作系统控制。

二、排他锁和共享锁

实际用的比较少

/**
 *
 * 共享锁： 所有程序都能多共享的部分进行读
 * 排他锁： 只有一个程序对锁定的部分进行写操作
 *
 */
public class NioTest10 {

    public static void main(String[] args) throws Exception {
        RandomAccessFile randomAccessFile = new RandomAccessFile("NioTest10.txt", "rw");

        FileChannel fileChannel = randomAccessFile.getChannel();

       FileLock fileLock = fileChannel.lock(3,6,true);

        System.out.println("valid:" + fileLock.isValid());

        System.out.println("lock type:" + fileLock.isShared());

        fileLock.release();

        randomAccessFile.close();
    }
}

　　

三、关于Buffer的Scattering（散开）与Gathering（收集）

/**
 *
 * 关于Buffer的Scattering（散开）与Gathering（收集）
 *
 */
public class NioTest11 {

    public static void main(String[] args) throws Exception {

        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();

        InetSocketAddress address = new InetSocketAddress(8899);

        serverSocketChannel.socket().bind(address);

        int messageLength = 2 + 3 + 4;
        ByteBuffer[] buffers = new ByteBuffer[3];
        buffers[0] = ByteBuffer.allocate(2);
        buffers[1] = ByteBuffer.allocate(3);
        buffers[2] = ByteBuffer.allocate(4);

        SocketChannel socketChannel = serverSocketChannel.accept();

        while (true){
            int byteRead = 0;
            while (byteRead < messageLength){
                long r = socketChannel.read(buffers);
                byteRead += r;

                System.out.println("bytesRead:" + byteRead);

                Arrays.asList(buffers).stream().map(buffer -> "position:" + buffer.position() +",limit:" + buffer.limit() + " 值：" + buffer.toString()).forEach(System.out::println);
            }

            Arrays.asList(buffers).forEach(buffer -> {
                buffer.flip();
            });

            long byteWritten = 0;
            while (byteWritten < messageLength){
                long r = socketChannel.write(buffers);
                byteWritten += r;
            }

            Arrays.asList(buffers).forEach(bufffer -> {
                bufffer.clear();
            });

            System.out.println("bytesRead:" + byteRead + ",byteWritten: " + byteWritten +", messageLength:" + messageLength);
        }

    }
}

　　使用Telnet发送，输出结果如下图：