用 nio 写一个文件上传

好的，下面是一个简单的基于 NIO 的文件上传示例代码：

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.SocketChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class FileUploader {

    private static final int BUFFER_SIZE = 1024;

    public static void main(String[] args) throws IOException {
        // 服务端监听的端口号
        int port = 8888;
        // 要接收的文件保存的目录
        Path saveDir = Paths.get("/path/to/save/dir");
        
        // 创建服务端 SocketChannel
        try (ServerSocketChannel serverChannel = ServerSocketChannel.open()) {
            serverChannel.socket().bind(new InetSocketAddress(port));
            System.out.println("Server started on port " + port);
            
            // 循环等待客户端连接
            while (true) {
                SocketChannel clientChannel = serverChannel.accept();
                System.out.println("Client connected: " + clientChannel.getRemoteAddress());
                
                // 解析客户端发送的文件名和文件大小
                ByteBuffer buffer = ByteBuffer.allocate(2 * Integer.BYTES);
                clientChannel.read(buffer);
                buffer.flip();
                int fileNameLength = buffer.getInt();
                int fileSize = buffer.getInt();
                
                // 接收文件数据并保存到本地文件
                Path savePath = saveDir.resolve(new String(buffer.array(), Integer.BYTES, fileNameLength));
                try (FileChannel fileChannel = FileChannel.open(savePath, StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE)) {
                    buffer = ByteBuffer.allocate(BUFFER_SIZE);
                    int bytesRead;
                    while ((bytesRead = clientChannel.read(buffer)) != -1) {
                        buffer.flip();
                        fileChannel.write(buffer);
                        buffer.compact();
                        if (fileChannel.position() == fileSize) {
                            break;
                        }
                    }
                    buffer.flip();
                    while (buffer.hasRemaining()) {
                        fileChannel.write(buffer);
                    }
                }
                
                System.out.println("File saved as " + savePath);
                clientChannel.close();
            }
        }
    }
}

客户端上传文件的代码如下：

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.SocketChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class FileUploader {

    private static final int BUFFER_SIZE = 1024;

    public static void main(String[] args) throws IOException {
        // 服务端的 IP 和监听的端口号
        String host = "localhost";
        int port = 8888;
        // 要上传的文件路径
        Path filePath = Paths.get("/path/to/upload/file");
        
        // 创建客户端 SocketChannel
        try (SocketChannel clientChannel = SocketChannel.open()) {
            clientChannel.connect(new InetSocketAddress(host, port));
            System.out.println("Connected to server: " + clientChannel.getRemoteAddress());
            
            // 发送文件名和文件大小
            String fileName = filePath.getFileName().toString();
            ByteBuffer buffer = ByteBuffer.allocate(2 * Integer.BYTES + fileName.length());
            buffer.putInt(fileName.length());
            buffer.putInt((int) Files.size(filePath));
            buffer.put(fileName.getBytes());
            buffer.flip();
            clientChannel.write(buffer);
            
            // 发送文件数据
            try (FileChannel fileChannel = FileChannel.open(filePath, StandardOpenOption.READ)) {
                buffer = ByteBuffer.allocate(BUFFER_SIZE);
                int bytesRead;
                while ((bytesRead = fileChannel.read(buffer)) != -1) {
                    buffer.flip();
                    clientChannel.write(buffer);
                    buffer.compact();
                }
                buffer.flip();
                while (buffer.hasRemaining()) {
                    clientChannel.write(buffer);
                }
            }
            
            System.out.println("File uploaded successfully");
        }
    }
}

这里只是一个简单的示例代码，实际应用中还需要考虑一些异常和错误处理等问题。