this is basic scenario for Developing Reporting application
we want to Design Report by Visual tools  , and by Simple API pass
variable and parameters from application.
and in the last step export it to some format based on User Requirement

in ideal case , JasperReport support some VisualTools for Designing
Your Report ,
and you can fill it by differenet way from different datasource ,
passing sql command or passing List of Bean ,
(Table Model, Map, XML and custom Datasources) supported too, and
at the last step you can export it to rich format.

JasperReport also support some other thirdparty tools for generating
powerfull reports ,
iText, JFreeChart, Jakarta POI.

but i think this is magic from jasperReport ,
it can integare friendly with your application ,
from the weblayer to persistence layer , Hibernate, Struts, Spring, JSF.

also , in some cases you need to generate full dunamic report from the
user interaction , the only solution  for this is manipulating your
jasper xml files ,
this can be Magic with Velocity from apache
from the IBM Solution :

www-128.ibm.com/.../0505_olivie\
ri/0505_olivieri.html

at the last JasperReport is mature java  Reporting Framework.