要实现Java的离线文件传输，可以使用Socket编程来实现。下面是一个简单的离线文件传输的示例代码：
服务端代码：
import java.io.*;import java.net.*;public class Server {public static void main(String[] args) {try {ServerSocket serverSocket = new ServerSocket(8888);System.out.println("等待客户端连接...");Socket socket = serverSocket.accept();System.out.println("客户端已连接");// 接收文件InputStream in = socket.getInputStream();FileOutputStream out = new FileOutputStream("file.txt");byte[] buffer = new byte[1024];int len;while ((len = in.read(buffer)) != -1) {out.write(buffer, 0, len);}out.close();in.close();System.out.println("文件接收完成");socket.close();serverSocket.close();} catch (IOException e) {e.printStackTrace();}}}客户端代码：
import java.io.*;import java.net.*;public class Client {public static void main(String[] args) {try {Socket socket = new Socket("localhost", 8888);// 发送文件File file = new File("file.txt");FileInputStream in = new FileInputStream(file);OutputStream out = socket.getOutputStream();byte[] buffer = new byte[1024];int len;while ((len = in.read(buffer)) != -1) {out.write(buffer, 0, len);}out.close();in.close();System.out.println("文件发送完成");socket.close();} catch (IOException e) {e.printStackTrace();}}}以上代码中，服务端通过ServerSocket监听指定的端口，客户端通过Socket连接到服务端。客户端将文件读取为字节流，通过Socket的输出流发送给服务端，服务端接收数据并写入文件。
