java ftp下载文件

以下是使用Java实现FTP文件下载的示例代码：

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

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

        FTPClient ftpClient = new FTPClient();
        try {
            ftpClient.connect(server, port);
            ftpClient.login(user, pass);
            ftpClient.enterLocalPassiveMode();
            ftpClient.setFileType(FTP.BINARY_FILE_TYPE);

            OutputStream outputStream = new FileOutputStream(localPath);
            InputStream inputStream = ftpClient.retrieveFileStream(remotePath);
            byte[] bytesArray = new byte[4096];
            int bytesRead = -1;
            while ((bytesRead = inputStream.read(bytesArray)) != -1) {
                outputStream.write(bytesArray, 0, bytesRead);
            }

            boolean success = ftpClient.completePendingCommand();
            if (success) {
                System.out.println("File has been downloaded successfully.");
            }
            outputStream.close();
            inputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (ftpClient.isConnected()) {
                    ftpClient.logout();
                    ftpClient.disconnect();
                }
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    }
}

在上面的示例代码中，首先我们使用FTPClient连接到FTP服务器，然后登录并设置传输模式和文件类型。接下来，我们使用retrieveFileStream()方法从远程FTP服务器下载文件，将其保存到本地文件系统中。最后，我们使用completePendingCommand()方法告诉FTP服务器已经完成了文件传输。最后，记得关闭所有的流和连接。