Problem in creating executable jar in Eclipse

Question

I'm working on a desktop program made in Java (Eclipse). The program transfers data from a pdf file to a Google sheets document. So far it works fine in Eclipse.
I'm running into problems when I'm trying to create a runable jar. It is made as a gradle project.

Error:

  Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError: 
  com/google/api/client/json/JsonFactory
        at SheetsAndJava.ProgramFrame.actionPerformed(ProgramFrame.java:132)
        at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
        at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
        at java.awt.Component.processMouseEvent(Unknown Source)
        at javax.swing.JComponent.processMouseEvent(Unknown Source)
        at java.awt.Component.processEvent(Unknown Source)
        at java.awt.Container.processEvent(Unknown Source)
        at java.awt.Component.dispatchEventImpl(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Window.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
        at java.awt.EventQueue.access$500(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at 
        
      java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown 
      Source)
        at 
       java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown 
 Source)
       at java.awt.EventQueue$4.run(Unknown Source)
       at java.awt.EventQueue$4.run(Unknown Source)
       at java.security.AccessController.doPrivileged(Native Method)
       at 
       java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown 
       Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
       at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
       at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
       at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
       at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
       at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
       at java.awt.EventDispatchThread.run(Unknown Source)
     Caused by: java.lang.ClassNotFoundException: com.google.api.client.json.JsonFactory
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 37 more

Thank you!