如何使用Java实现FTP客户端的源码?

import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;
import java.io.IOException;
public class FTPExample {
    public static void main(String[] args) {
        // 创建FTPClient对象
        FTPClient ftpClient = new FTPClient();
        try {
            // 连接到FTP服务器
            ftpClient.connect("ftp.example.com");
            System.out.println("Connected to " + ftpClient.getHost());
            // 登录到FTP服务器
            if (ftpClient.login("username", "password")) {
                System.out.println("Login successful");
                // 切换到指定目录
                ftpClient.changeWorkingDirectory("/path/to/directory");
                // 列出当前目录下的文件和文件夹
                FTPFile[] files = ftpClient.listFiles();
                for (FTPFile file : files) {
                    System.out.println("File: " + file.getName() + ", Size: " + file.getSize());
                }
                // 下载文件
                String remoteFilePath = "/path/to/remote/file";
                String localFilePath = "/path/to/local/file";
                boolean success = ftpClient.retrieveFile(remoteFilePath, new FileOutputStream(localFilePath));
                if (success) {
                    System.out.println("File downloaded successfully");
                } else {
                    System.out.println("Failed to download file");
                }
                // 上传文件
                String uploadRemoteFilePath = "/path/to/upload/remote/file";
                String uploadLocalFilePath = "/path/to/upload/local/file";
                InputStream inputStream = new FileInputStream(uploadLocalFilePath);
                boolean uploadSuccess = ftpClient.storeFile(uploadRemoteFilePath, inputStream);
                inputStream.close();
                if (uploadSuccess) {
                    System.out.println("File uploaded successfully");
                } else {
                    System.out.println("Failed to upload file");
                }
                // 注销并断开连接
                ftpClient.logout();
                ftpClient.disconnect();
            } else {
                System.out.println("Login failed");
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (ftpClient.isConnected()) {
                    ftpClient.disconnect();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

这个示例展示了如何使用Apache Commons Net库创建一个FTP客户端，连接到FTP服务器，登录，切换目录，列出文件，下载和上传文件，然后注销并断开连接，请根据实际情况修改服务器地址、用户名、密码、文件路径等参数。

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