Spring can't see my imported classes-Collection of common programming errors

My controller (abstract controller) is calling a service class to get a URL. In my service class I instantiate my dependency in the constructor:

the abstract controller:

public class MyPageController extends AbstractController{
private UserService userService;
private LearnerService learnerService;
private TwitterService twitterService;
@Override
protected ModelAndView handleRequestInternal(HttpServletRequest request,
                HttpServletResponse response) throws Exception {
        userService = UserServiceFactory.getUserService();
        learnerService = new LearnerService();
        twitterService=new TwitterService();

the Service class:

public TwitterService(){
        //
        twitter = new Twitter();
}

but when I try to run my web app, spring throws the following error:

nested exception is java.lang.NoClassDefFoundError: twitter4j/Twitter:
    java.lang.NoClassDefFoundError: twitter4j/Twitter
    at com.hardwire.service.TwitterService.(Twitter Service.java:21)
    at com.hardwire.controller.
    MyPageController.handleReq uestInternal(MyPageController.java:30)

Why does it throw this error? I don’t understand. I imported the Twitter class in the service class that uses it.