Problem

If you’re working with a server-side application, like I am, that imports a 

javax.swing
package, you might get strange errors, such as the one described here. 
javax.swing
packages expect to find an X11 server running on the machine. In my case, it wants to access the graphical subsystem because JFreeReport wants to use a 
TableModel
as a kind of spreadsheet.

Solution

append 

java.awt.headless=true
to your 
JAVA_OPTS<pre> in catalina.sh.  Mine ended up looking like this.</p>
              
              <pre>
              JAVA_OPTS=-Dsalmon.props.path=/home/opgi/bin/jakarta-tomcat-4.1.30/salmon/properties
              JAVA_OPTS = "$JAVA_OPTS -Djava.awt.headless=true" 
              </pre>