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DMA：direct memory access，直接内存拷贝，不使用CPU

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// java io 服务器
public class OldIOServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(6666);
        while (true) {
            Socket socket = serverSocket.accept();
            DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
            try {
                byte[] byteArray = new byte[4096];
                while (true) {
                    int readCount = dataInputStream.read(byteArray, 0, byteArray.length);
                    if (-1 == readCount) {
                        break;
                    }
                }
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }

    }
}

public class OldIOClient {
    public static void main(String[] args) throws IOException {
        Socket socket = new Socket("localhost", 6666);
        String fileName = "C:\\Users\\32582\\Desktop\\mf.log";
        InputStream inputStream = new FileInputStream(fileName);
        DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());

        byte[] buffer = new byte[4096];
        long readCount;
        long total = 0;

        long startTime = System.currentTimeMillis();
        while ((readCount = inputStream.read(buffer)) >= 0) {
            total += readCount;
            dataOutputStream.write(buffer);
        }

        System.out.println("发送总字节数：" + total + ", 耗时：" + (System.currentTimeMillis() - startTime));

        dataOutputStream.close();
        socket.close();
        inputStream.close();

    }
}

public class NewIOServer {
    public static void main(String[] args) throws IOException {
        InetSocketAddress address = new InetSocketAddress(6666);
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        ServerSocket serverSocket = serverSocketChannel.socket();
        serverSocket.bind(address);

        // 创建 buffer
        ByteBuffer byteBuffer = ByteBuffer.allocate(4096);
        while (true) {
            SocketChannel socketChannel = serverSocketChannel.accept();
            int readCount = 0;
            while (-1 != readCount) {
                readCount = socketChannel.read(byteBuffer);
            }
            byteBuffer.rewind(); // 倒带 position = 0 mark 作废
        }
    }
}

public class NewIOClient {
    public static void main(String[] args) throws IOException {
        SocketChannel socketChannel = SocketChannel.open();
        socketChannel.connect(new InetSocketAddress("localhost", 6666));
        String fileName = "C:\\Users\\32582\\Desktop\\mf.log";
        // 得到一个文件 channel
        FileChannel fileChannel = new FileInputStream(fileName).getChannel();
        // 准备发送
        long startTime = System.currentTimeMillis();
        // 在 linux 下一个transferTo 方法就可以完成传输
        // 在 windows 下一次调用 transferTo 只能发送 8m, 就需要分段传输文件，而且要注意传输时的位置
        // transferTo 底层使用到零拷贝
        long transferCount = fileChannel.transferTo(0, fileChannel.size(), socketChannel);
        System.out.println("发送总字节数：" + transferCount + ", 耗时：" + (System.currentTimeMillis() - startTime));

        fileChannel.close();
    }
}

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