java - Jackson JSON 和 Hibernate JPA 问题的无限递归

Question

当尝试将具有双向关联的 JPA 对象转换为 JSON 时，我不断收到

org.codehaus.jackson.map.JsonMappingException: Infinite recursion (StackOverflowError)

我找到的只是 this thread其结论基本上是建议避免双向关联。有谁知道这个 spring bug 的解决方法吗？

------编辑2010-07-24 16:26:22 -------

代码片段:

业务对象1:

@Entity
@Table(name = "ta_trainee", uniqueConstraints = {@UniqueConstraint(columnNames = {"id"})})
public class Trainee extends BusinessObject {

    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    @Column(name = "id", nullable = false)
    private Integer id;

    @Column(name = "name", nullable = true)
    private String name;

    @Column(name = "surname", nullable = true)
    private String surname;

    @OneToMany(mappedBy = "trainee", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @Column(nullable = true)
    private Set<BodyStat> bodyStats;

    @OneToMany(mappedBy = "trainee", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @Column(nullable = true)
    private Set<Training> trainings;

    @OneToMany(mappedBy = "trainee", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @Column(nullable = true)
    private Set<ExerciseType> exerciseTypes;

    public Trainee() {
        super();
    }

    //... getters/setters ...
}

业务对象2:

import javax.persistence.*;
import java.util.Date;

@Entity
@Table(name = "ta_bodystat", uniqueConstraints = {@UniqueConstraint(columnNames = {"id"})})
public class BodyStat extends BusinessObject {

    @Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    @Column(name = "id", nullable = false)
    private Integer id;

    @Column(name = "height", nullable = true)
    private Float height;

    @Column(name = "measuretime", nullable = false)
    @Temporal(TemporalType.TIMESTAMP)
    private Date measureTime;

    @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name="trainee_fk")
    private Trainee trainee;
}

Controller :

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.http.HttpServletResponse;
import javax.validation.ConstraintViolation;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;

@Controller
@RequestMapping(value = "/trainees")
public class TraineesController {

    final Logger logger = LoggerFactory.getLogger(TraineesController.class);

    private Map<Long, Trainee> trainees = new ConcurrentHashMap<Long, Trainee>();

    @Autowired
    private ITraineeDAO traineeDAO;
     
    /**
     * Return json repres. of all trainees
     */
    @RequestMapping(value = "/getAllTrainees", method = RequestMethod.GET)
    @ResponseBody        
    public Collection getAllTrainees() {
        Collection allTrainees = this.traineeDAO.getAll();

        this.logger.debug("A total of " + allTrainees.size() + "  trainees was read from db");

        return allTrainees;
    }    
}

JPA-实习生 DAO 的实现:

@Repository
@Transactional
public class TraineeDAO implements ITraineeDAO {

    @PersistenceContext
    private EntityManager em;

    @Transactional
    public Trainee save(Trainee trainee) {
        em.persist(trainee);
        return trainee;
    }

    @Transactional(readOnly = true)
    public Collection getAll() {
        return (Collection) em.createQuery("SELECT t FROM Trainee t").getResultList();
    }
}

持久性.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
             version="1.0">
    <persistence-unit name="RDBMS" transaction-type="RESOURCE_LOCAL">
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name="hibernate.hbm2ddl.auto" value="validate"/>
            <property name="hibernate.archive.autodetection" value="class"/>
            <property name="dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect"/>
            <!-- <property name="dialect" value="org.hibernate.dialect.HSQLDialect"/>         -->
        </properties>
    </persistence-unit>
</persistence>

Answer 1

JsonIgnoreProperties [2017 更新]:

您现在可以使用JsonIgnoreProperties 抑制属性的序列化(在序列化期间)，或忽略对读取的 JSON 属性的处理(在反序列化期间)。如果这不是您要找的内容，请继续阅读下面的内容。

(感谢 As Zammel AlaaEddine 指出了这一点)。

<小时/>

JsonManagedReference 和 JsonBackReference

从 Jackson 1.6 开始，您可以使用两个注释来解决无限递归问题，而无需在序列化期间忽略 getter/setter: @JsonManagedReference 和 @JsonBackReference .

说明

为了让 Jackson 正常工作，关系的两侧之一不应被序列化，以避免无限循环导致 stackoverflow 错误。

因此，Jackson 获取引用文献的前部(Trainee 类中的 Set<BodyStat> bodyStats)，并将其转换为类似 json 的存储格式；这就是所谓的编码过程。然后，Jackson 查找引用的后面部分(即 BodyStat 类中的 Trainee trainee)并保持原样，而不对其进行序列化。这部分关系将在前向引用的反序列化(解码)过程中重新构建。

您可以像这样更改代码(我跳过无用的部分):

业务对象 1:

@Entity
@Table(name = "ta_trainee", uniqueConstraints = {@UniqueConstraint(columnNames = {"id"})})
public class Trainee extends BusinessObject {

    @OneToMany(mappedBy = "trainee", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @Column(nullable = true)
    @JsonManagedReference
    private Set<BodyStat> bodyStats;

业务对象 2:

@Entity
@Table(name = "ta_bodystat", uniqueConstraints = {@UniqueConstraint(columnNames = {"id"})})
public class BodyStat extends BusinessObject {

    @ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name="trainee_fk")
    @JsonBackReference
    private Trainee trainee;

现在一切都应该可以正常工作了。

如果您想了解更多信息，我写了一篇关于 Json and Jackson Stackoverflow issues on Keenformatics 的文章，我的博客。

编辑:

您可以检查的另一个有用的注释是 @JsonIdentityInfo :使用它，每次 Jackson 序列化你的对象时，它都会向它添加一个 ID(或你选择的另一个属性)，这样它就不会每次都再次完全“扫描”它。当您在更多相互关联的对象之间有一个链循环时(例如:Order -> OrderLine -> User -> Order 等等)，这会很有用。

在这种情况下，您必须小心，因为您可能需要多次读取对象的属性(例如，在包含多个共享同一卖家的产品的产品列表中)，并且此注释会阻止您执行以下操作:所以。我建议始终查看 firebug 日志以检查 Json 响应并查看代码中发生了什么。

来源:

• Keenformatics - How To Solve JSON infinite recursion Stackoverflow (我的博客)
• 个人经历