public Object getExpressionValue (String expression) 
throws Exception

This method calculates the value of an expression inside a tag. The expression may be a reference to the object's attribute (attribute path) or a more complicated arithmetic expression. If the expression contains the formatting expression, the result is converted to the specified format; otherwise it is converted to the format specified in the attribute (if a single attribute is used). The fillWithData method can use the Object.toString () method to convert the result to String and put it in the output document instead of the tag.

The value of the expression - possible types of the Java object are presented in the table of the correspondence between attribute and Java types in the Appendix A. Null can be returned if the value is undefined.

An exception if the value cannot be calculated for whatever reason.