使用JPA 2和EJB 3.1“没有会话或会话已关闭” [英] 'no session or session was closed' with JPA 2 and EJB 3.1

问题描述

我有这种方法的无状态会话bean：

  @Override 
 public List< Character> getUserCharacters（int userId）{
 User user = em.find（User.class，userId）; 
 if（user！= null）
返回user.getCharacters（）; 
 else 
返回null; 
 
  

其中用户类如果以这种方式定义的话：

  @Entity 
 @Table（name =Users）
 public class User实现Serializable {
 
 / ** * / 
 
 private static final long serialVersionUID = 8119486011976039947L; 
 
 @Id 
 @GeneratedValue（strategy = GenerationType.SEQUENCE）
 private int id; 
 
 @ManyToMany（fetch = FetchType.EAGER）
 private Set< Role>角色; 
 
 @OneToMany（mappedBy =owner，fetch = FetchType.LAZY）
 private List< com.AandP.game.model.characters.Character>字符; 
 $ b $ public User（）{
 creationDate = new Date（）; 
 roles = new HashSet< Role>（）; 
 
 
 $ / code> 

但是当我执行这个方法时（从我的<$



  org.hibernate.LazyInitializationException：失败c $ c> @Named  bean）我收到异常：
懒惰地初始化一个角色集合：com.AandP.game.model.User.characters，没有会话或会话被关闭
  

根据JPA 2.0规范，会话应该在整个事务中保持活跃状态​​。在这种情况下，交易（在我看来）持续一个完整的方法调用（对于类或方法没有额外的事务属性）。

所以问题是：什么是这段代码有问题，我怎么才能加载类属性。

$ b $ JPA 2.0规范会话应该在整个事务中保持活跃状态​​。在这种情况下，交易（在我看来）持续一个完整的方法调用（在类或方法上没有额外的事务属性）。

这是真的，但它不包括所返回对象的序列化。

我将导出会话bean的问题与web服务相同。详细了解此处的问题。

如果您有类似的用法，强烈建议您返回普通对象而不是实体。你可以像我们一样使用一些bean映射框架。我们使用了推土机。

I have stateless session bean with this method:

@Override
public List<Character> getUserCharacters(int userId) {
    User user = em.find(User.class, userId);
    if(user != null)
        return user.getCharacters();
    else
        return null;
}

where User class if defined in this way:

@Entity
@Table(name="Users")
public class User implements Serializable{

    /**  */

private static final long serialVersionUID = 8119486011976039947L;

@Id
@GeneratedValue(strategy=GenerationType.SEQUENCE)
private int id;

@ManyToMany(fetch=FetchType.EAGER)
private Set<Role> roles;

@OneToMany(mappedBy="owner",fetch=FetchType.LAZY)
private List<com.AandP.game.model.characters.Character> characters;

public User() {
    creationDate = new Date();
    roles = new HashSet<Role>();
    }
}

But when i execute this method (from my @Named bean) i receive exception:

 org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.AandP.game.model.User.characters, no session or session was closed

According to the JPA 2.0 specification session should stay alive for a whole transaction. In this situation transaction (in my opinion) last for a whole method call (there is no additional transaction attributes on class or method).

So the question is: what is wrong with this code and how can I load class properties in a lazy way.

解决方案

According to the JPA 2.0 specification session should stay alive for a whole transaction. In this situation transaction (in my opinion) last for a whole method call (there is no additional transaction attributes on class or method).

That's true, but it does not include the serialization of the returned objects.

I had the same issue exporting a session bean as a web service. Read more about the issue here.

If you have a similar use would strongly suggest you to return plain objects and not entities. You can use some bean mapping framework like we did. We used Dozer.

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