使用spring和hibernate来获取多个表数据无法正常工作-UI-提交响应后无法调用sendError（）

Question

我有三个表，分别是Forum ， ForumAnswer和ForumAnswerReplay 。 该表包含@OneToMany关系。 我有论坛表主键。 基于该主键，我需要获取ForumAnswer和ForumAnswerReplay数据。

但是反应还没有达到ui side 。

堆栈跟踪

ResponseStatusExceptionResolver：133-从处理程序[公共java.util.List com.tta.abcd.controller.ForumController.getReplayToAnswer（javax.servlet.http.HttpSession）]中解析异常：org.springframework.http.converter.HttpMessageNotWritableException：无法编写内容：无限递归（StackOverflowError）

Forum.java

    @Entity
    @Table(name="Forum")
    public class Forum {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="forumId")
    private Long forumId;

    @Column(name="question")
    private String question;

    @Column(columnDefinition="varchar(1000)",name="discription")
    private String discription;

    @Column(name="postedDate")
    private Date postedDate;

    @Fetch(value = FetchMode.SELECT)
    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "forumId")
    @JsonIgnore
    private List<ForumAnswer> forumList;
    }

ForumAnswer.java

@Entity
@Table(name="ForumAnswer")
public class ForumAnswer {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="forumAnswerId")
    private Long forumAnswerId;


    @ManyToOne
    @JoinColumn(name = "forumId",insertable=true, updatable=true,nullable=true)
    private Forum forum;

    @Column(name="answer")
    private String answer;

    @Column(name="answerDate")
    private Date answerDate;

    @Fetch(value = FetchMode.SELECT)
    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "forumAnswerId")
    @JsonManagedReference
    private List<ForumAnswerReplay> forumAnswerReplayList;
    }

ForumAnswerReplay.java

 @Entity
 @Table(name="ForumAnswerReplay")
 public class ForumAnswerReplay {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="replayId")
    private Long replayId;

    @Column(name="replayToAnswer")
    private String replayToAnswer;

    @Column(name="replayToAnswerDate")
    private Date replayToAnswerDate;


    @ManyToOne
    @JoinColumn(name="forumAnswerId",insertable=true,updatable=true,nullable=true)
    @JsonBackReference
    private ForumAnswer forumAnswer;
    }

控制器代码：

@RequestMapping(value = "/getForumOnIdAnswer", method = RequestMethod.POST)
@ResponseBody
public List<ForumAnswer> getForumAnswerOnId(@RequestBody Long id, HttpSession session,
        HttpServletResponse httpServletResponse, HttpServletRequest httpServletRequest) {
    List<ForumAnswer> forumAnswer = forumService.getForumAnswerOnId(id);
    if (forumAnswer != null) {
        return forumAnswer;
    }
    return forumAnswer;
}

DAO：

public List<ForumAnswer> getForumAnswerOnId(Long id) {
    Long forumId = id;
    List<ForumAnswer> ForumAnswerTemp = new ArrayList<ForumAnswer>();
    List<ForumAnswerReplay> ForumAnswerReplayTemp = new ArrayList<ForumAnswerReplay>();
    Long forumAnswerId = null;
    ForumAnswer forumTemp = new ForumAnswer();
    ForumAnswer forumEntity = new ForumAnswer();


    String getForumAnswer = "from ForumAnswer WHERE forumId =:forumId order by answerDate Desc";
    Query query = sessionFactory.getCurrentSession().createQuery(getForumAnswer);
    query.setParameter("forumId", forumId);

    List<ForumAnswer> forumList = query.list();
    int count =forumList.size();
    if ( count> 0) {
        for (int i=1 ; i < count ;i++) {
            forumEntity =forumList.get(i);
            forumAnswerId = forumList.get(i).getForumAnswerId();
            List<ForumAnswerReplay> repltList = getreplayList(forumAnswerId);
            if (repltList.size() > 0) {
                ForumAnswerReplayTemp.addAll(repltList);
                forumEntity.setForumAnswerReplayList(ForumAnswerReplayTemp);
                ForumAnswerTemp.add(forumEntity);
            } else {
                ForumAnswerTemp.add(forumEntity);
            }
        }
    }
    return ForumAnswerTemp;
}

public List<ForumAnswerReplay> getreplayList(Long forumAnswerId) {
    String getForumAnswer = "from ForumAnswerReplay WHERE forumAnswerId =:forumAnswerId";
    Query query = sessionFactory.getCurrentSession().createQuery(getForumAnswer);
    query.setParameter("forumAnswerId", forumAnswerId);
    List<ForumAnswerReplay> replays = query.list();
    return replays;

}

Answer 1

可能是您需要在impl类上使用@Transactional批注。

@Transactional的关键点之一是要考虑两个单独的概念，每个概念都有自己的范围和生命周期：

数据库事务的持久性上下文事务注释本身定义了单个数据库事务的范围。 数据库事务在持久性上下文的范围内发生。

持久性上下文在JPA中是EntityManager，使用Hibernate Session在内部实现（当使用Hibernate作为持久性提供程序时）。

持久性上下文只是一个同步器对象，该对象跟踪一组有限的Java对象的状态，并确保最终将这些对象上的更改持久化回到数据库中。

这与数据库事务的概念非常不同。 一个实体管理器可以跨多个数据库事务使用，实际上经常是这样。

https://dzone.com/articles/how-does-spring-transactional

Answer 2

在方法减速中使返回类型为String，然后将列表转换为映射并创建Model对象，然后在模型中设置映射。 然后返回您期望的jsp页面。

@ResponseBody @RequestMapping（value =“ / getForumOnIdAnswer”，方法= RequestMethod.POST）

public String yourList(@RequestBody Long id, Model model){

    List<ForumAnswer> forumAnswer = forumService.getForumAnswerOnId(id);
    if (forumAnswer != null) {

        // convert your list to Map then set in model. 
            model.addAttribute("forumAnswerMap",listToMap);
    }
    return "yourJspPage"
`

可能会对您有帮助。