问题描述
我尝试使用Java,Hibernate和Spring编写一些程序.调用SQL查询时,我看到NullPointerException.我可能尝试了Internet上所有的代码示例,但是我不知道该怎么做.我该如何解决?这是我的示例代码.我有完整的程序代码: https://github.com/lukasz-chojn/films_database/tree/master/src/main/java/Films
I try to write some programme using Java, Hibernate and Spring. I see NullPointerException when I call the SQL query. I tried perhaps every samples of code on the internet, but I don't know how to do this. How can I solve it? This is my sample code. There is my full code of programme: 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();
}
//....
}
推荐答案
您是自己创建实例,而不是让spring为您注入实例,这就是为什么您丢失所有依赖项(如Entitymanager等)的原因DataFromUserController
You're creating instances on your own instead of letting spring inject it for you which is why you're losing all the dependencies like entitymanager, etc. change your DataFromUserController
@Controller
public class DataFromUserController {
@Autowired
private FilmDAO filmDao;
@Autowired
private DirectorDAO directorDao;
.....
}
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