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，我不断得到

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

我所发现的就是这条线索，它的基本结论是建议避免双向关联。有没有人有办法解决这个spring bug？

------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;
}

控制器：

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-见习DAO的实施：

@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();
    }
}

坚持不懈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

新的注释@JsonIgnoreProperties解决了其他选项的许多问题。

@Entity

public class Material{
   ...    
   @JsonIgnoreProperties("costMaterials")
   private List<Supplier> costSuppliers = new ArrayList<>();
   ...
}

@Entity
public class Supplier{
   ...
   @JsonIgnoreProperties("costSuppliers")
   private List<Material> costMaterials = new ArrayList<>();
   ....
}

看看这里。它的工作原理就像在留档：
http://springquay.blogspot.com/2016/01/new-approach-to-solve-json-recursive.html

Answer 2

您可以使用@JsonIgnore来打破循环（参考）。

您需要导入org.codehaus.jackson.annotate.JsonIgnore（旧版）或com.fasterxml.jackson.annotation.JsonIgnore（当前版本）。

Answer 3

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

（感谢As Zammel AlaaEddine指出这一点）。

从Jackson 1.6开始，您可以使用两个注释来解决无限递归问题，而不会在序列化过程中忽略getter/setter：@JsonManaged参考和@JsonBack参考。

解释

为了让Jackson正常工作，不应该序列化关系的两个方面之一，以避免导致stackoverflow错误的infite循环。

因此，Jackson将引用的前半部分（你的集合）

您可以这样更改代码（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;

现在这一切都应该正常工作了。

如果你想要更多的信息，我写了一篇关于Json和Jackson Stackoverflow问题的文章在我的博客Keenformtics上。

编辑：

您可以检查的另一个有用注释是@JsonIdtyInfo：使用它，每次Jackson序列化您的对象时，它都会向其添加一个ID（或您选择的另一个属性），这样它就不会每次都完全“扫描”它。当您在更多相互关联的对象之间有一个链式循环时，这可能会很有用（例如：订单-

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，在一个产品列表中，有多个产品共享同一卖家），而此注释阻止您这样做。我建议经常查看firebug日志，检查Json响应，看看代码中发生了什么。

资料来源：

• Keenformtics-如何解决JSON无限递归Stackoverflow（我的博客）
• 杰克逊参考
• 个人经历