JavaNIO中的内存映射io

Posted 2021-02-02

客户端代码：

package cc.client;

import java.io.*;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.*;

public class ClientOper {
    public static void main(String[] args) throws IOException {
        
        File file=new File("test.txt");
        
        RandomAccessFile raf=new RandomAccessFile(file, "rw"); 
        FileChannel fileChannel=raf.getChannel();
        //内存映射，将内核缓存区的内存进行映射，应用程序可以像操作用户缓存区一样向内核缓存区读写数据。
        MappedByteBuffer mbb=fileChannel.map(FileChannel.MapMode.READ_WRITE, 0,1024 );
        //写入数据
        for(int i=0;i<1024;i++)
            mbb.put((byte)‘c‘);
        raf.close();
        
        /* SocketChannel sChannel = SocketChannel.open();
            sChannel.configureBlocking(false);
            //建立连接
            sChannel.connect(new InetSocketAddress("127.0.0.1", 80));
        
        
        
          while (!sChannel.finishConnect()) {
            System.out.println("等待非阻塞连接建立....");
            try {
              Thread.sleep(10);
            } catch (InterruptedException e) {
              e.printStackTrace();
            }
          }
         
         
        //这时依旧需要CPU将内核缓冲区的内容拷贝到网络缓冲区
        while(mbb.hasRemaining()) {
            sChannel.write(mbb);
        }
        fileChannel.close();
        raf.close();*/
        
        
        //测试消息成功写入了test文件
        /*FileInputStream fs=new FileInputStream(file);
        
        byte[] bytes=new byte[1024];
          StringBuilder stringb=new StringBuilder();
          //开始读消息
          int length;
          while((length=fs.read(bytes))!=-1) {
              
              stringb.append(new String(bytes,0,length));
          }
          System.out.println(stringb);
          fs.close();*/
        
        
        
         
    }
}
        
        
        
    

服务端代码：

public class ServerOper {

    
    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
        ServerSocketChannel serverSocket = ServerSocketChannel.open();
        serverSocket.bind(new InetSocketAddress(80));
        serverSocket.configureBlocking(false);
        
         SocketChannel socketChannel = null;
         while(socketChannel==null) {
             socketChannel=serverSocket.accept();
         }
         ByteBuffer byteBuffer=ByteBuffer.allocate(1024);
         int numByetsRead;
          while((numByetsRead = socketChannel.read(byteBuffer)) != -1) {
              
              if (numByetsRead == 0) {
                  // 如果没有数据，则稍微等待一下
                  try {
                    Thread.sleep(1);
                  } catch (InterruptedException e) {
                    e.printStackTrace();
                  }
                  continue;
                }
                // 转到最开始
                byteBuffer.flip();
                while (byteBuffer.remaining() > 0) {
                  System.out.print((char) byteBuffer.get());
                }

        
              
          }
          
          socketChannel.close();
          serverSocket.close();
         

    }

}

参考：JavaNIO和零拷贝（Zero Copy）

           https://www.linuxtopia.org/online_books/programming_books/thinking_in_java/TIJ314_029.htm