我刚刚开始使用EJB。我想用JTA从数据库中接收一些数据。我的实体:
@Entity
@Table(name = "User")
@NamedQuery(name = "User.findByAddressName",
query = "select u from User u where u.userAddress.addressName = :addressName")
public class User implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private long userID;
@Column(name = "userFirstName", length = 45)
private String userFirstName;
@Column(name = "userLastName", length = 45)
private String userLastName;
@Column(name = "userBirthDate")
private Date userBirthDate;
@Column(name = "userPhone")
private String userPhone;
@Column(name = "userPassword")
private String userPassword;
@OneToOne(cascade = CascadeType.ALL, mappedBy = "addressUser")
private Email userAddress;
public User() {
}
public User(String userFirstName, String userLastName, Date userBirthDate, String userPhone, String userPassword) {
this.userFirstName = userFirstName;
this.userLastName = userLastName;
this.userBirthDate = userBirthDate;
this.userPhone = userPhone;
this.userPassword = userPassword;
}
}
我的道:
@Stateless
public class UserBean {
@PersistenceContext(unitName = "server")
private EntityManager em;
public User getUserByEmail(String email) {
TypedQuery<User> queryUser = em.createNamedQuery("User.findByAddressName",
User.class);
queryUser.setParameter("addressName", email);
return queryUser.getSingleResult();
}
}
我的服务:
@Stateless
public class LoginService {
@EJB
UserBean userBean;
public boolean loginUser(String userEmail, String userPass) {
User user = userBean.getUserByEmail(userEmail);
if (userPass.equals(user.getUserPassword())) {
return true;
} else return false;
}
}
我尝试接收数据:
boolean b = new LoginService().loginUser("user", "user1");
但是@EJB在LoginService中注入的UserBean UserBean是空的。
有很多简单的例子如何做这样的事情,我做的都完全一样,但它仍然抛出NullPointerException,我不知道为什么。
要受益于Java EE环境中的注入,您不能通过new
实例化您的服务。您需要通过@EJB
注入它,或者使用JNDI查找它。
如果你通过new
创建你的服务,这个实例不被认为是容器管理的实例,所以它的任何功能(比如注入)都是不可用的。当您注入它或通过JNDI查找它的引用时,您将获得完全托管的实例,所有注入都为您完成。
不知道你在哪个Java EE堆栈上(5或6),但请记住,你不能简单地通过@EJB
注入到手工创建的类中。