生成一段JAVA，FTP下载文件的代码

以下是使用Apache Commons Net库实现FTP下载文件的JAVA代码：

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.SocketException;
import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;

public class FTPDownloader {

    public static void main(String[] args) {
        String server = "ftp.example.com";
        int port = 21;
        String user = "username";
        String pass = "password";
        String remoteFilePath = "/remote/file/path/file.txt";
        String localFilePath = "C:/local/file/path/file.txt";

        FTPClient ftpClient = new FTPClient();

        try {
            // Connect to FTP server
            ftpClient.connect(server, port);
            ftpClient.login(user, pass);
            ftpClient.enterLocalPassiveMode();
            ftpClient.setFileType(FTP.BINARY_FILE_TYPE);

            // Download file
            InputStream inputStream = ftpClient.retrieveFileStream(remoteFilePath);
            FileOutputStream outputStream = new FileOutputStream(localFilePath);
            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
            inputStream.close();
            outputStream.close();

            // Logout and disconnect from FTP server
            ftpClient.logout();
            ftpClient.disconnect();
        } catch (SocketException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

在代码中，您需要替换以下变量：

- `server` - FTP服务器的地址
- `port` - FTP服务器的端口
- `user` - 登录FTP服务器的用户名
- `pass` - 登录FTP服务器的密码
- `remoteFilePath` - 要下载的远程文件的路径和文件名
- `localFilePath` - 要保存到本地的文件的路径和文件名

您还需要在项目中包含Apache Commons Net库的依赖项。可以使用Maven添加以下依赖项：

<dependency>
    <groupId>commons-net</groupId>
    <artifactId>commons-net</artifactId>
    <version>3.7</version>
</dependency>