@Override和@Transactional注解

Question

我使用jpa，eclispelink和Spring3。我有UserDAO接口：

  public interface UserDAO {
    public void saveUser(User user);
  }

和实现类：

@Service
@Transactional
public class UserDAOImpl implements UserDAO{

@PersistenceContext
EntityManager em;

@Override
public void saveUser(User user) {
    em.persist(user);
}

当我启动应用程序时，我得到了错误：

HTTP Status 500 - Servlet.init() for servlet appServlet threw exception<br>
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'cartController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: foo.endpoints.UserEndpoint foo.controller.CartController.userEndpoint; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userEndpoint': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: foo.dao.UserDAOImpl foo.endpoints.UserEndpoint.userDAO; nested exception is java.lang.IllegalArgumentException: Can not set foo.dao.UserDAOImpl field foo.endpoints.UserEndpoint.userDAO to com.sun.proxy.$Proxy16

org.springframework.beans.factory.BeanCreationException: Could not autowire field: foo.endpoints.UserEndpoint foo.controller.CartController.userEndpoint; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userEndpoint': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: foo.dao.UserDAOImpl foo.endpoints.UserEndpoint.userDAO; nested exception is java.lang.IllegalArgumentException: Can not set foo.dao.UserDAOImpl field foo.endpoints.UserEndpoint.userDAO to com.sun.proxy.$Proxy16

但是如果我不实现接口：

 @Service
 @Transactional
 public class UserDAOImpl {
 @PersistenceContext
 EntityManager em;
  public void saveUser(User user) {
  em.persist(user);
  }

一切正常。我不明白。也许是因为@Override方法的原因？谢谢

Answer 1

如果为bean定义了接口，则必须注入接口的实例，而不是具体类的实例：

@Autowired
private UserDAO userDAO;

而不是

@Autowired
private UserDAOImpl userDAOImpl;

因为实际的bean实例是实现接口并调用您的实现的JDK动态代理。它不是UserDAOImpl的实例。