如何从另外一台服务器上下载文件夹，java

您可以使用Java中的FTP客户端库来从另一台服务器上下载文件夹。您需要使用FTP协议连接到远程服务器，然后使用FTP客户端库中的方法下载文件夹。以下是一个简单的Java代码示例，可以从远程服务器下载文件夹：

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;

import java.io.IOException;

public class FTPDownloadFolderExample {

    public static void main(String[] args) {
        String server = "remote.server.com";
        int port = 21;
        String user = "username";
        String pass = "password";
        String remoteFolderPath = "/path/to/remote/folder";
        String localFolderPath = "/path/to/local/folder";

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

            downloadFolder(ftpClient, remoteFolderPath, localFolderPath);

            ftpClient.logout();
            ftpClient.disconnect();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    private static void downloadFolder(FTPClient ftpClient, String remoteFolderPath, String localFolderPath) throws IOException {
        ftpClient.changeWorkingDirectory(remoteFolderPath);
        String[] subDirectories = ftpClient.listNames();
        for (String subDirectory : subDirectories) {
            if (subDirectory.equals(".") || subDirectory.equals("..")) {
                continue;
            }
            String remoteSubDirectoryPath = remoteFolderPath + "/" + subDirectory;
            String localSubDirectoryPath = localFolderPath + "/" + subDirectory;
            downloadFolder(ftpClient, remoteSubDirectoryPath, localSubDirectoryPath);
        }
        String[] files = ftpClient.listFiles();
        for (String file : files) {
            String remoteFilePath = remoteFolderPath + "/" + file;
            String localFilePath = localFolderPath + "/" + file;
            ftpClient.retrieveFile(remoteFilePath, new FileOutputStream(localFilePath));
        }
    }
}

在这个示例中，我们使用了Apache Commons Net库中的FTP客户端来连接到远程服务器，并使用递归函数下载了整个文件夹。请注意，您需要将`server`，`port`，`user`，`pass`，`remoteFolderPath`和`localFolderPath`替换为实际的值。