use commons-net and commons-pool2 to build ftp connection pool
To use it in your Maven build add:
<repositories>
<repository>
<id>jitpack.io</id>
<url>https://jitpack.io</url>
</repository>
</repositories>
and the dependency:
<dependency>
<groupId>com.github.honwhy</groupId>
<artifactId>ftpcp2</artifactId>
<version>0.0.1-20200112</version>
</dependency>