title: java.lang.NoClassDefFoundError library apache poi netbeans
body: <p>I am trying to use the apache POI in order to handle some xlsx files.I downloaded the zip and added the JAR files to the libraries.When I used the apache POI classes to my project they were found(the project found no errors) but when I ran the project i got the java.lang.NoClassDefFoundError. 
     What could be the possible problem?(the JARS are added correctly).Thank you </p>