On my Gentoo machine the "Show in System Explorer" menu item did not work on Eclipse. I kept getting this error message:
Execution of 'dbus-send --print-reply --dest=org.freedesktop.FileManager1
/org/freedesktop/FileManager1 org.freedesktop.FileManager1.ShowItems
array:string:"file:/tmp/HelloWorld.java" string:""' failed with return code: 1
The expose-filemanager.py script exposes a dbus object that implements the freedesktop File Manager DBus specification. This makes the Eclipse "Show in System Explorer" menu item work.
Just start the script in the background.