To work with filesystems that were created outside of the IDE, you must mount them in the IDE. Likewise, any libraries that your project depends on need to be mounted for your project to run in the IDE.
For Java applications, mounted directories must be mounted at the default package. The sources in the directories must be in packages corresponding to their position relative to the mount point. If a filesystem of Java sources is mounted at the wrong point, the IDE can not compile the sources, and other problems will arise.
For example, if you have multiple source trees with the package root of each tree grouped together under one directory, you have to mount each package root separately. In the following structure
src app com myapp myapp.java lib com mylib mylib.javawhere app and lib are the package roots, you can not simply mount src. You have to mount app and lib separately.
If you you want the classes from a JAR file to be included in the classpath for applications you work with in the IDE, that JAR file must be mounted individually as an archive file.
To mount a directory in the IDE:
To mount a JAR or ZIP archive in the IDE: