java nio file transfer example

使用nio传输文件需要注意的是会出现粘包和服务器端缓冲区满的情况。第一种情况，客户端发送30次数据，而服务器端只接收到18次的情况，这种情况出现 主要是服务器端是以流的方式接收数据，它并不知道每次客户端传输数据的大小而造成的。第二种情况是服务器端缓冲区满，导致客户端数据传输失败，这种情况 下，需要判断传输int send = client.write(sendBuffer)的send值，如果send值为0,则服务器端的数据缓冲区可能满了。

客户端实现代码：

import java.io.FileInputStream;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Set;
  
public class FileClient {
    private int port = 8000;
    /* 发送数据缓冲区 */
    private static ByteBuffer sendBuffer = ByteBuffer.allocate(1024);
    /* 接受数据缓冲区 */
    private static ByteBuffer revBuffer = ByteBuffer.allocate(1024);
    private InetSocketAddress SERVER;
    private static Selector selector;
    private static SocketChannel client;
      
    public FileClient(){
        try{
            SERVER = new InetSocketAddress("localhost", port);
            init();
        }
        catch(Exception e){
            e.printStackTrace();
        }
          
    }
    private void init(){
        try {
            SocketChannel socketChannel = SocketChannel.open();
            socketChannel.configureBlocking(false);
            selector = Selector.open();
            socketChannel.register(selector, SelectionKey.OP_CONNECT);
            socketChannel.connect(SERVER);
            while (true) {
                selector.select();
                Set<SelectionKey> keySet = selector.selectedKeys();
                for (final SelectionKey key : keySet) {
                    if(key.isConnectable()){
                        client = (SocketChannel)key.channel();
                        client.finishConnect();
                        client.register(selector, SelectionKey.OP_WRITE);
  
                    }
                    else if(key.isWritable()){
                        sendFile(client);
                    }
                }
                keySet.clear();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
      
    private void sendFile(SocketChannel client) {
        FileInputStream fis = null;
        FileChannel channel = null;
        try {
//          fis = new FileInputStream("E:\\1.txt");
//          fis = new FileInputStream("E:\\1.rar");
            fis = new FileInputStream("G:\\3.rar");
            channel = fis.getChannel();
            int i = 1;
            int count = 0;
            while((count = channel.read(sendBuffer)) != -1) {
                sendBuffer.flip(); 
                int send = client.write(sendBuffer);
                System.out.println("i===========" + (i++) + "   count:" + count + " send:" + send);
                // 服务器端可能因为缓存区满，而导致数据传输失败，需要重新发送
                while(send == 0){
                    Thread.sleep(10);
                    send = client.write(sendBuffer);
                    System.out.println("i重新传输====" + i + "   count:" + count + " send:" + send);
                }
                sendBuffer.clear(); 
           }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                channel.close();
                fis.close();
                client.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
  
        }
    }
      
      
    public static void main(String[] args){
        new FileClient();
    }
}

服务器端

import java.io.FileOutputStream;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Set;
  
public class FileServer {
    private int port = 8000;
    /* 发送数据缓冲区 */
    private static ByteBuffer revBuffer = ByteBuffer.allocate(1024);
    private static Selector selector;
    private static FileOutputStream fout;
    private static FileChannel ch;
    public FileServer(){
        try{
            init();
        }
        catch(Exception e){
            e.printStackTrace();
        }
    }
    private void init() throws Exception{
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.configureBlocking(false);
        ServerSocket serverSocket = serverSocketChannel.socket();
        serverSocket.bind(new InetSocketAddress(port));
        selector = Selector.open();
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("server start on port:" + port);
        while (true) {
            try {
                selector.select();// 返回值为本次触发的事件数
                Set<SelectionKey> selectionKeys = selector.selectedKeys();
                  
                for (SelectionKey key : selectionKeys) {
                    ServerSocketChannel server = null;
                    SocketChannel client = null;
                    int count = 0;
                    if (key.isAcceptable()) {
                        server = (ServerSocketChannel) key.channel();
                        System.out.println("有客户端连接进入=============)");
                        client = server.accept();
                        client.configureBlocking(false);
                        client.register(selector, SelectionKey.OP_READ);
                        fout = new FileOutputStream("G:\\" + client.hashCode() + ".rar");
                        ch = fout.getChannel();
                    } else if (key.isReadable()) {
                        client = (SocketChannel) key.channel();
                        revBuffer.clear();
                        count = client.read(revBuffer);
                        int k = 0;
                        // 循环读取缓存区的数据，
                        while(count > 0){
                            System.out.println("k=" + (k++) + " 读取到数据量:" + count);
                            revBuffer.flip();
                            ch.write(revBuffer);
                            fout.flush();
                            revBuffer.clear();
                            count = client.read(revBuffer);
                        }
                        if(count == -1){
                            client.close();
                            ch.close();
                            fout.close();
                        }
                    }
                    else if (key.isWritable()) {
                        System.out.println("selectionKey.isWritable()");
                      
                    }
                }
                System.out.println("=======selectionKeys.clear()");
                selectionKeys.clear();
            } catch (Exception e) {
                e.printStackTrace();
                break;
            }
  
        }
    }
    public static void main(String[] args){
        new FileServer();
    }
}