调用实体管理器时的java空指针
我试着用Java、Hibernate和Spring编写一些程序。调用SQL查询时,我看到NullPointerException。我尝试了互联网上的每一个代码示例,但我不知道如何做到这一点。我怎样才能解决它?这是我的示例代码。这是我的完整节目代码:https://github.com/lukasz-chojn/films_database/tree/master/src/main/java/Films
@Controller
public class DataFromUserController {
private FilmDaoImpl filmDaoImpl = new FilmDaoImpl();
private DirectorDaoImpl directorDaoImpl = new DirectorDaoImpl();
private Locale locale = Locale.getDefault();
private Scanner sc = new Scanner(System.in).useLocale(locale);
public FilmDs collectData() {
//....
filmDaoImpl.insert(film);
directorDaoImpl.insert(director);
return film;
}
private String collectTitle() {
System.out.print("Podaj tytuł filmu: ");
String tytul = sc.nextLine();
List<String> existingEntry = filmDaoImpl.existingTitle();
if (existingEntry.contains(tytul)) {
System.out.println("Tytuł jest już w bazie. Podaj inny");
return collectTitle();
}
if (tytul.isEmpty()) {
System.out.println("Tytuł nie może być pusty. Podaj go");
return collectTitle();
}
return tytul;
}//......
}
@Service
@Transactional
public class FilmDaoImpl implements FilmDAO {
@PersistenceContext
private EntityManager entityManager;
//......
@Override
@SuppressWarnings("unchecked")
public List<String> existingTitle() {
List<String> titleInTheDatabase;
// here is NPE
return titleInTheDatabase = entityManager.createQuery("SELECT film.tytul FROM FilmDs film").getResultList();
}
//....
}
# 1 楼答案
您自己创建实例,而不是让spring为您注入实例,这就是您丢失所有依赖项(如entitymanager等)的原因