How to use external JAR file in JasperSoft Studio

I have project in iReport, I want to build this in jasper studio,in that I use some external jar file to convert date, but in jasper studio I cant use them, I add those jar file in `right click on project folder > properties > java build path > libraries > add External JARs..`, I get error when I want to see report preview : ``` net.sf.jasperreports.engine.JRException: Errors were encountered when compiling report expressions class file: 1. com.ghasemkiani.util.icu.PersianDateFormat cannot be resolved to a type value = new com.ghasemkiani.util.icu.PersianDateFormat("yyyy/MM/dd").format(((java.sql.Timestamp)field_ORDERDATE.getValue())); //$JR_EXPR_ID=9$ <----------------------------------------> 2. com.ghasemkiani.util.icu.PersianDateFormat cannot be resolved to a type value = new com.ghasemkiani.util.icu.PersianDateFormat("yyyy/MM/dd").format(((java.sql.Timestamp)field_ORDERDATE.getOldValue())); //$JR_EXPR_ID=9$ <----------------------------------------> ``` so,my question is : how can I add external jar file and use it?