Right click on your project > click properties at the bottom > click Libraries on the left side > click Add Jar or Add External Jar > Locate the Jar file and load it > click OK. Now you have added the related Jar file into your class path and the ClassNotFoundException should disappear. If still issue is unresolved, you need to open the Jar file with JD-GUI and check if the class you are looking for is present or not. If yes it should resolve the error, if not, then you should upgrade or downgrade the jar depending upon the situation.