When trying to export on WebLogic 11g, it throws NoClassDefFound exception. I checked the application WAR and jasperreports-3.7.4.jar is included in WEB-INF/lib folder. What
This was due to a missing font. I was able to resolve this by installing fontconfig and urw-fonts packages.
yum install fontconfig yum install urw-fonts
After that you can check supported fonts using command
fc-list
If the reports are still not generated you may need to reboot the server.