Using Tomcat and Xalan, why do I get the exception: java.lang.IllegalStateException: Response has already been committed when trying to pass quot;out" to the XSLTProcessor as a XSLTResultTarget?

Most of the time, when I had this exception, it was because Tomcat was unable to find a given class (CLASSPATH problem).

Check that all your class files are in Tomcat CLASSPATH (you can easily check it when you start Tomcat, as this information is printed to stdout)