A simple SFTP Server implemented using Apache Mina SSHD library using Java and Spring boot. To start the server , just run the JavaSftpserverApplication class and after that type the following command to start a SFTP session.

sftp -oPort=2222 test@localhost

You can read more explanation about how it is implemented at :

https://programmingtechie.com/2019/02/23/how-to-implement-an-sftp-server-in-java-spring-boot-using-apache-mina-sshd/

https://programmingtechie.com/2019/08/18/how-to-implement-an-sftp-server-in-java-spring-boot-using-apache-mina-sshd-part-2-using-public-key-authentication/