I'd recommend managing your dependent libraries with maven.
<dependency>
<groupId>org.controlsfx</groupId>
<artifactId>controlsfx</artifactId>
<version>11.1.0</version>
</dependency>
If you don't want to use maven and you really want to copy the jar file to your local file system, the jars can also be found in the maven repository at
https://mvnrepository.com/Just search for the name of your library, then click on the jar link in the Files section of the resulting table.