我有这样一个问题:
org.hibernate.LazyInitializationException:惰性初始化role: mvc3.model.Topic.comments集合失败，没有会话或会话已关闭
下面是模型:
@Entity
@Table(name = "T_TOPIC")
public class Topic {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int id;
@ManyToOne
@JoinColumn(name="USER_ID")
private User author;
@Enumerated(EnumType.STRING)
private Tag topicTag;
private String name;
private String text;
@OneToMany(mappedBy = "topic", cascade = CascadeType.ALL)
private Collection<Comment> comments = new LinkedHashSet<Comment>();
...
public Collection<Comment> getComments() {
return comments;
}
}
调用model的控制器如下所示:
@Controller
@RequestMapping(value = "/topic")
public class TopicController {
@Autowired
private TopicService service;
private static final Logger logger = LoggerFactory.getLogger(TopicController.class);
@RequestMapping(value = "/details/{topicId}", method = RequestMethod.GET)
public ModelAndView details(@PathVariable(value="topicId") int id)
{
Topic topicById = service.findTopicByID(id);
Collection<Comment> commentList = topicById.getComments();
Hashtable modelData = new Hashtable();
modelData.put("topic", topicById);
modelData.put("commentList", commentList);
return new ModelAndView("/topic/details", modelData);
}
}
jsp页面看起来如下所示:
<%@page import="com.epam.mvc3.helpers.Utils"%>
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page session="false" %>
<html>
<head>
<title>View Topic</title>
</head>
<body>
<ul>
<c:forEach items="${commentList}" var="item">
<jsp:useBean id="item" type="mvc3.model.Comment"/>
<li>${item.getText()}</li>
</c:forEach>
</ul>
</body>
</html>
在查看jsp时，将引发异常。在c:forEach循环的行中
不是最好的解决方案，但对于那些面临LazyInitializationException的人，特别是在序列化上，这将有所帮助。在这里，您将检查惰性初始化属性并将其设置为null。为此，创建以下类
public class RepositoryUtil {
public static final boolean isCollectionInitialized(Collection<?> collection) {
if (collection instanceof PersistentCollection)
return ((PersistentCollection) collection).wasInitialized();
else
return true;
}
}
在你的实体类中，你有一个惰性初始化的属性，添加如下所示的方法。在这个方法中添加所有延迟加载属性。
public void checkLazyIntialzation() {
if (!RepositoryUtil.isCollectionInitialized(yourlazyproperty)) {
yourlazyproperty= null;
}
在加载数据的所有位置之后调用这个checklazyinitialize()方法。
YourEntity obj= entityManager.find(YourEntity.class,1L);
obj.checkLazyIntialzation();
此问题是由于在关闭hibernate会话的情况下访问属性造成的。控制器中没有hibernate事务。
可能的解决方式:
Do all this logic, in the service layer, (with the @Transactional), not in the controller. There should be the right place to do this, it is part of the logic of the app, not in the controller (in this case, an interface to load the model). All the operations in the service layer should be transactional.
i.e.: Move this line to the TopicService.findTopicByID method:
Collection commentList = topicById.getComments();
Use 'eager' instead of 'lazy'. Now you are not using 'lazy' .. it is not a real solution, if you want to use lazy, works like a temporary (very temporary) workaround.
use @Transactional in the Controller. It should not be used here, you are mixing service layer with presentation, it is not a good design.
use OpenSessionInViewFilter, many disadvantages reported, possible instability.
一般来说，最佳解是1。
在第二次执行生成JWT令牌的方法后，我得到了这个错误。
line user.getUsersRole().stream().forEachOrdered((ur) -> roles.add(ur. getroleid ()));生成错误。
// MyUserDetails.java
@Service
public class MyUserDetails implements UserDetailsService {
@Override
public UserDetails loadUserByUsername(String email) {
/* ERROR
/* org.hibernate.LazyInitializationException: failed to
/* lazily initialize a collection of role:
/* com.organizator.backend.model.User.usersRole,
/* could not initialize proxy - no Session */
user.getUsersRole().stream().forEachOrdered((ur) ->
roles.add(ur.getRoleId()));
在我的例子中，@Transactional注释解决了它，
// MyUserDetails.java
import org.springframework.transaction.annotation.Transactional;
@Service
public class MyUserDetails implements UserDetailsService {
@Override
@Transactional // <-- added
public UserDetails loadUserByUsername(String email) {
/* No Error */
user.getUsersRole().stream().forEachOrdered((ur) ->
roles.add(ur.getRoleId()));
