DISPLAY variable needed for Filling a report?

Hello out there,

I generated a nice report with iReport and now
I want to use a litte java program to generate reports in "batch" on a linux server. I
coded this little piece of snippet:

import net.sf.jasperreports.engine.*;
import java.util.HashMap;
public class runReport
{
public static void main(String[] args)
{
JasperReport jasperReport;
JasperPrint jasperPrint;
try
{
jasperReport = JasperCompileManager.compileReport(
"../hrmodul/Jobs.jrxml");
jasperPrint = JasperFillManager.fillReport(
jasperReport, new HashMap(), new JREmptyDataSource());
JasperExportManager.exportReportToPdfFile(
jasperPrint, "../hrmodul/simple_report.pdf");
}
catch (JRException e)
{
e.printStackTrace();
}
}
}

And there is the problem, it throws me an exception in line with the FillManager:
Exception in thread "main" java.lang.InternalError: Can't connect to X11 window server using ':0.0' as the value of the DISPLAY variable.
at sun.awt.X11GraphicsEnvironment.initDisplay(Native Method)
at sun.awt.X11GraphicsEnvironment.<clinit>(X11GraphicsEnvironment.java:175)
at java.lang.Class.forName1(Native Method)
at java.lang.Class.forName(Class.java:180)
at java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment(GraphicsEnvironment.java:91)
at net.sf.jasperreports.engine.util.JRGraphEnvInitializer.initializeGraphEnv(JRGraphEnvInitializer.java:58)

and so on...

What is this? I don't want to SHOW the report.

Many thanks.
Frank