Question

我建立了一对多的关系。尽管当我从多个侧面通过ID查询对象时，一切似乎都很好，但joined列会引发stackoverflow异常，但我无法弄清楚它为什么会发生。大约我已经遵循this tutorial。

玩家实体

@Entity
@Data
public class Player {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "player_id", updatable = false, unique = true, nullable = false)
    private Long id;
    @Column(name = "name")
    private String name;
    @Column(name = "num")
    private int num;
    @Column(name = "position")
    private String position;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "team_id")
    private Team team;
}

团队实体

@Entity
@Data
public class Team {
    @Id
    @Column(name="team_id", updatable = false, unique = true)
    private String id;
    @Column(name = "name")
    private String name;
    @OneToMany(mappedBy = "team")
    private List<Player> players;
}

我的玩家资料库

@Repository
public interface PlayerRepository extends CrudRepository<Player, Long> {
    Optional<Player> findById(Long id);
}

import.sql中的数据库条目

insert into Team (team_id,name) values('Barcelona','Barcelona');
insert into Player (name,num,position,team_id) values('Andreas Inniesta', 8, 'Midfielder', 'Barcelona');
insert into Player (name,num,position,team_id) values('Lionel Messi', 10, 'Forward', 'Barcelona');

H2控制台上的播放器表

这是例外

java.lang.StackOverflowError: null
        at java.lang.StringBuilder.append(StringBuilder.java:136) ~[na:1.8.0_121]
        at mypackage.entity.Player.toString(Player.java:8) ~[classes!/:1.0-SNAPSHOT]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_121]
        at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:510) ~[hibernate-core-5.2.17.Final.jar!/:5.2.17.Final]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at mypackage.entity.Team.toString(Team.java:9) ~[classes!/:1.0-SNAPSHOT]
        at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source) ~[na:na]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_121]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_121]
        at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:84) ~[hibernate-core-5.2.17.Final.jar!/:5.2.17.Final]
        at mypackage.entity.Team_$$_jvst2b7_1.toString(Team_$$_jvst2b7_1.java) ~[classes!/:1.0-SNAPSHOT]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at mypackage.entity.Player.toString(Player.java:8) ~[classes!/:1.0-SNAPSHOT]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_121]
        at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:510) ~[hibernate-core-5.2.17.Final.jar!/:5.2.17.Final]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at mypackage.entity.Team.toString(Team.java:9) ~[classes!/:1.0-SNAPSHOT]
        at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source) ~[na:na]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_121]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_121]
        at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:84) ~[hibernate-core-5.2.17.Final.jar!/:5.2.17.Final]
        at mypackage.entity.Team_$$_jvst2b7_1.toString(Team_$$_jvst2b7_1.java) ~[classes!/:1.0-SNAPSHOT]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at mypackage.entity.Player.toString(Player.java:8) ~[classes!/:1.0-SNAPSHOT]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_121]
        at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:510) ~[hibernate-core-5.2.17.Final.jar!/:5.2.17.Final]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at mypackage.entity.Team.toString(Team.java:9) ~[classes!/:1.0-SNAPSHOT]
        at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source) ~[na:na]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_121]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_121]
        at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:84) ~[hibernate-core-5.2.17.Final.jar!/:5.2.17.Final]
        at mypackage.entity.Team_$$_jvst2b7_1.toString(Team_$$_jvst2b7_1.java) ~[classes!/:1.0-SNAPSHOT]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at mypackage.entity.Player.toString(Player.java:8) ~[classes!/:1.0-SNAPSHOT]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_121]
        at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:510) ~[hibernate-core-5.2.17.Final.jar!/:5.2.17.Final]
        at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
        at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
        at mypackage.entity.Team.toString(Team.java:9) ~[classes!/:1.0-SNAPSHOT]
        at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source) ~[na:na]

例外的根源

at mypackage.entity.Team.toString(Team.java:9) ~[classes!/:1.0-SNAPSHOT]
at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source) ~[na:na]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_121]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_121]
at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:84) ~[hibernate-core-5.2.17.Final.jar!/:5.2.17.Final]
at mypackage.entity.Team_$$_jvst2b7_1.toString(Team_$$_jvst2b7_1.java) ~[classes!/:1.0-SNAPSHOT]
at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
at mypackage.entity.Player.toString(Player.java:8) ~[classes!/:1.0-SNAPSHOT]
at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
at java.util.AbstractCollection.toString(AbstractCollection.java:462) ~[na:1.8.0_121]
at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:510) ~[hibernate-core-5.2.17.Final.jar!/:5.2.17.Final]
at java.lang.String.valueOf(String.java:2994) ~[na:1.8.0_121]
at java.lang.StringBuilder.append(StringBuilder.java:131) ~[na:1.8.0_121]
at mypackage.entity.Team.toString(Team.java:9) ~[classes!/:1.0-SNAPSHOT]
at sun.reflect.GeneratedMethodAccessor43.invoke(Unknown Source) ~[na:na]

进一步调试该错误表明，在连接的列上某种内部转换为字符串失败。

Answer 1

如我所见，您正在使用Lombok。

您认为您没有在创建toString方法，但是Lombok却不这么认为。 @Data注释会导致生成toString方法。

摘自Lombok文档：

@Data是一个方便的快捷方式注释，它捆绑了以下功能 @ToString，@EqualsAndHashCode，@Getter / @Setter和 @RequiredArgsConstructor在一起：换句话说，@Data生成所有通常与简单POJO相关联的样板（普通旧Java对象）和bean：所有字段的获取器，所有字段的获取器非最终字段，以及适当的toString，equals和hashCode 涉及类领域的实现，以及初始化所有final字段以及所有没有初始值设定项的非最终字段已标记为 @NonNull，以确保该字段永远不会为空。

因此Lombok为您创建了toString方法，这导致了无限递归。

您可以通过以下方式修复它：

@ToString(exclude = "players")
public class Team {
   // ...
}

或者：

@ToString(exclude = "players")
public class Team {
    @OneToMany(mappedBy = "team")
    @ToString.Exclude
    private List<Player> players;
}

值得一提的是，如果您仍然需要在players的{{1}}表示中包含Team，请尝试反汇编toString批注并仅添加您真正需要的部分需要。然后定义自己的@Data方法。

Answer 2

发生这种情况的原因是，当您要查询团队“ A”时，该列表还包含一个“ A”团队中的球员列表，这些球员本身就是他们所在的团队（“ A”团队），其中还包含玩家列表...您明白了，它在这种关系中无限循环无休止。为了避免StackOverflow错误，如果使用的是Jackson，则需要使用@JsonIgnore注释@OneToMany的一侧；如果使用的是普通的jsonb，则需要使用@JsonbTransient注释。

@OneToMany(mappedBy = "team")
@JsonIgnore
private List<Player> players;

OR

@OneToMany(mappedBy = "team")
@JsonbTransient
private List<Player> players;

这样，在查询球队时，球员名单将被忽略，您将避免出现错误。

Answer 3

即使我也遇到过类似的问题。我在尝试保持一对多关系时遇到了StackoverFlow错误。解决方法是。

@Data
@EqualsAndHashCode(exclude = "players")   // players is @OneToMany
 class Team {
  @OneToMany(mappedBy = "team")
   private List<Player> players;
 }

这引起了问题，因为它曾经使用所有实体创建哈希码。这导致递归。

一对多关系导致休眠中的堆栈溢出

3 个答案: