SFTPClient

import org.apache.sshd.client.SshClient;
import org.apache.sshd.client.session.ClientSession;
import org.apache.sshd.sftp.client.SftpClient;
import org.apache.sshd.sftp.client.SftpClientFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

public class SftpClientWithKeyAuth {
    private static final Logger logger = LoggerFactory.getLogger(SftpClientWithKeyAuth.class);
    private static final String HOST = "localhost";
    private static final int PORT = 2222;
    private static final String USERNAME = "your_username";
    private static final String PRIVATE_KEY_PATH = "path/to/your/private_key";

    private final SshClient client;

    public SftpClientWithKeyAuth() {
        this.client = SshClient.setUpDefaultClient();
    }

    public void connect() throws IOException {
        client.start();
        ClientSession session = client.connect(USERNAME, HOST, PORT)
                .verify(10000)
                .getSession();

        session.addPublicKeyIdentity(Paths.get(PRIVATE_KEY_PATH));
        session.auth().verify(30000);

        logger.info("Successfully connected to SFTP server");
    }

    public void uploadFile(String localFilePath, String remoteFilePath) throws IOException {
        try (ClientSession session = client.connect(USERNAME, HOST, PORT).verify(10000).getSession()) {
            session.addPublicKeyIdentity(Paths.get(PRIVATE_KEY_PATH));
            session.auth().verify(30000);

            SftpClient sftpClient = SftpClientFactory.instance().createSftpClient(session);

            try (InputStream inputStream = Files.newInputStream(Paths.get(localFilePath));
                 OutputStream outputStream = sftpClient.write(remoteFilePath)) {

                byte[] buffer = new byte[8192];
                int length;
                while ((length = inputStream.read(buffer)) != -1) {
                    outputStream.write(buffer, 0, length);
                }
            }

            logger.info("File uploaded successfully: {}", remoteFilePath);
        }
    }

    public void downloadFile(String remoteFilePath, String localFilePath) throws IOException {
        try (ClientSession session = client.connect(USERNAME, HOST, PORT).verify(10000).getSession()) {
            session.addPublicKeyIdentity(Paths.get(PRIVATE_KEY_PATH));
            session.auth().verify(30000);

            SftpClient sftpClient = SftpClientFactory.instance().createSftpClient(session);

            try (InputStream inputStream = sftpClient.read(remoteFilePath);
                 OutputStream outputStream = Files.newOutputStream(Paths.get(localFilePath))) {

                byte[] buffer = new byte[8192];
                int length;
                while ((length = inputStream.read(buffer)) != -1) {
                    outputStream.write(buffer, 0, length);
                }
            }

            logger.info("File downloaded successfully: {}", localFilePath);
        }
    }

    public void disconnect() throws IOException {
        client.stop();
        logger.info("Disconnected from SFTP server");
    }

    public static void main(String[] args) {
        SftpClientWithKeyAuth client = new SftpClientWithKeyAuth();
        try {
            client.connect();

            // Example usage
            client.uploadFile("path/to/local/file.txt", "/remote/path/file.txt");
            client.downloadFile("/remote/path/file.txt", "path/to/local/downloaded_file.txt");

            client.disconnect();
        } catch (IOException e) {
            logger.error("Error occurred during SFTP operations", e);
        }
    }
}