FTPClient读取单个文件

好的，以下是使用Apache Commons Net库中的FTPClient读取单个文件的步骤：

1. 创建FTPClient对象并连接到FTP服务器：

FTPClient ftpClient = new FTPClient();
ftpClient.connect(server, port);
ftpClient.login(username, password);

2. 设置FTPClient以二进制模式传输文件：

ftpClient.setFileType(FTP.BINARY_FILE_TYPE);

3. 切换到需要读取文件的目录：

ftpClient.changeWorkingDirectory(remoteFilePath);

4. 使用retrieveFile()方法读取文件：

OutputStream outputStream = new BufferedOutputStream(new FileOutputStream(localFile));
ftpClient.retrieveFile(fileName, outputStream);
outputStream.close();

其中，remoteFilePath是FTP服务器上文件所在的路径，fileName是需要读取的文件名，localFile是本地存储文件的路径和文件名。

5. 断开FTP连接：

ftpClient.logout();
ftpClient.disconnect();

完整的代码示例：

import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.OutputStream;

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

public class FTPClientDemo {

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

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

            ftpClient.changeWorkingDirectory(remoteFilePath);

            OutputStream outputStream = new BufferedOutputStream(new FileOutputStream(localFilePath));
            ftpClient.retrieveFile(fileName, outputStream);
            outputStream.close();
            
            ftpClient.logout();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (ftpClient.isConnected()) {
                    ftpClient.disconnect();
                }
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }
}

希望这可以帮助到您！