SFTPTransfer

SFTPTransfer is a background file transfer service that moves files between a local filesystem and a remote SFTP server. It is a standalone Java application that runs either as a headless background service or as a desktop application with a minimal GUI, and supports both uploading (PUT) and downloading (GET) in independent threads.

SFTPTransfer replaces the earlier sftpSend and sftpGet tools with a unified, configurable service.

Purpose

SFTPTransfer automates recurring file transfers between Commander4j and external systems — for example, uploading despatch notifications to a customer portal or downloading order files from a supplier. It runs continuously, polling for new files at a configurable interval, and handles authentication, retry, backup, and archiving without operator involvement.

Startup Modes

SFTPTransfer supports two startup modes selected at launch time:

Mode	Behaviour
Start desktop	Opens a small GUI window. Transfer threads start in a paused state; the operator must click Start in the interface to begin polling. Useful for testing configuration.
Start service	Headless — no GUI window. Transfer threads start immediately on launch. Suitable for production deployment as a background service or scheduled task.

On Windows, the native install package includes sftpTransfer_Service.exe, which manages the Windows service directly — see Installing as a Windows Service below. On Linux/macOS, use systemd, launchd, or nohup.

Configuration Files

All configuration is held in XML files under the xml/config/ directory. Changes require a service restart unless hot-reload is triggered (see below).

sftp_common.xml

Shared settings used by all transfer threads:

Setting	Description
Poll interval	How often (in seconds) each thread checks for new files. Default: 10 seconds.
Backup retention	Number of days to keep backed-up files before automatic deletion.
Log level	Logging verbosity passed to Log4j.

sftp_put.xml

Configures one or more PUT (upload) profiles. Each profile defines:

Setting	Description
Enabled	Whether this profile's thread is active.
Local path	Local directory to watch for outbound files.
File mask	Wildcard pattern to match files (e.g. *.xml, order_*.csv). Uses Apache Commons IO WildcardFileFilter.
Remote host	SFTP server hostname or IP address.
Remote port	SFTP port (default: 22).
Remote path	Target directory on the remote server.
Username	SFTP login username.
Password	AES-encrypted password (see Password Encryption).
Private key path	Path to SSH private key file (alternative to password authentication).
Backup path	Local directory where successfully uploaded files are moved.
Error path	Local directory where files that failed to upload are moved.

sftp_get.xml

Configures one or more GET (download) profiles. Each profile defines:

Setting	Description
Enabled	Whether this profile's thread is active.
Remote host	SFTP server hostname or IP address.
Remote port	SFTP port (default: 22).
Remote path	Directory on the remote server to poll for incoming files.
File mask	Wildcard pattern matched against the remote file listing (server-side ls).
Local path	Local directory where downloaded files are saved.
Username	SFTP login username.
Password	AES-encrypted password.
Private key path	Path to SSH private key file.
Delete after download	Whether to delete the remote file after successful download.
Backup path	Local directory where a copy of each downloaded file is kept.

jsch_properties.xml

Advanced SSH session parameters passed directly to the JSch library. Used to control host key checking, preferred algorithms, and connection timeouts. In most deployments this file can be left at its defaults.

email_properties.xml

SMTP settings for error notification emails. When a transfer failure occurs and email notification is enabled, SFTPTransfer sends an alert to the configured address. Fields include SMTP host, port, sender address, recipient address, and AES-encrypted SMTP password.

Installing as a Windows Service

The native install package includes sftpTransfer_Service.exe, a service-mode launcher built with install4j. This executable manages the Windows service directly — no additional wrapper is required.

All service commands must be run from an elevated command prompt (Run as Administrator).

Command	Effect
sftpTransfer_Service.exe /install	Register the Windows service with automatic startup on boot
sftpTransfer_Service.exe /install-demand	Register the service with manual startup only
sftpTransfer_Service.exe /start	Start the service
sftpTransfer_Service.exe /stop	Stop the service (waits for graceful shutdown)
sftpTransfer_Service.exe /restart	Restart the service
sftpTransfer_Service.exe /status	Query status (exit code: 0 = running, 3 = stopped)
sftpTransfer_Service.exe /uninstall	Remove the service registration

Once installed, the service also appears in the Windows Services management console (services.msc).

Testing Before Installing as a Service

The native install package also provides two alternatives for testing:

Launcher	Mode	Use case
sftpTransfer_Console.exe	Console (headless)	Runs the service logic in a visible console window — useful for watching log output during initial configuration
sftpTransfer.exe	Desktop GUI	Opens the GUI window in Start desktop mode — transfer threads start paused, allowing configuration to be verified before enabling transfers

Authentication

SFTPTransfer supports two authentication methods, configured per profile:

Method	How to configure
Password	Set the Password field in the profile to an AES-encrypted value. Leave the private key path empty.
SSH private key	Set the Private key path field to the path of a PEM-format private key file. The password field is ignored.

Both methods use the JSch 2.x SSH library with Bouncy Castle as the cryptographic provider.

Password Encryption

Passwords stored in configuration files are AES-encrypted. Plain-text passwords are never stored on disk. To encrypt a password, use the password utility included with Commander4j (the same utility used for database passwords in Commander4j's own configuration).

File Transfer Behaviour

PUT (Upload)

1. SFTPTransfer polls the local input directory every 10 seconds (configurable).
2. Files matching the file mask are selected for upload.
3. Each file is uploaded to the remote path using a temporary name with a .tmp extension.
4. On successful transfer, the remote file is renamed to its final name (atomic rename — the remote system never sees a partial file).
5. The local source file is moved to the backup directory.
6. If the transfer fails, the file is moved to the error directory and an error is logged.

GET (Download)

1. SFTPTransfer lists the remote directory every 10 seconds (configurable).
2. Files matching the file mask are selected for download.
3. Each file is downloaded to the local path using a .tmp extension.
4. On successful download, the local file is renamed to its final name.
5. If configured, the remote file is deleted after download.
6. A backup copy is optionally saved to the local backup directory.

Thread Architecture

When running, SFTPTransfer maintains the following threads:

Thread	Purpose
TransferPUT	One thread per enabled PUT profile, each managing its own SFTP connection.
TransferGET	One thread per enabled GET profile, each managing its own SFTP connection.
EmailThread	Sends error notification emails asynchronously.
ArchiveThread	Periodically purges backup files older than the configured retention period.

Hot Configuration Reload

SFTPTransfer supports a configuration reload mode (Mode_CONFIG_UPDATE). When this mode is triggered, running threads re-read their configuration files without requiring a full service restart. This allows profile changes — such as updating a remote path or rotating credentials — to be applied with minimal disruption.

Logging

All activity is written to the Log4j log file. The log records:

• Service startup and configuration loaded
• Each thread starting and its profile settings
• Every file detected, transfer attempted, and outcome
• Every remote connection attempt and disconnect
• File move operations (to backup or error directories)
• Errors and exceptions with full context

Log rotation and retention are configured in the Log4j configuration file included in the distribution.

Dependencies

Library	Version	Purpose
JSch	2.27.9	SSH/SFTP client
Bouncy Castle	current	Cryptographic provider for JSch
Apache Commons IO	current	WildcardFileFilter for local file matching
Log4j	2.25.3	Logging

See also: LabelServer4j, Middleware4j, Production Lines & Labellers