Finally, I’ve got it working. I detected the root Exception, which was thrown before NoClassDefFoundError:net/sf/jasperreports/engine/util/JRStyledTextParser :
java.lang.NoClassDefFoundError: sun/awt/X11GraphicsEnvironment
The Sun AWT classes on Unix and Linux have a dependence on the X Window System. When you use these classes, they expect to load X client libraries and be able to talk to an X display server. This makes sense if your client has a GUI; unfortunately, it’s required even if your client uses AWT but does not have a GUI (which is my case, generating a report from a web application)
The way to bypass this, is setting a system property java.awt.headless=true
on system startup.