调用toString方法会StackOverflowError的原因和解决方案

今天遇到一个问题，调用一个实体类的toString方法直接就StackOverflowError（栈溢出）了。

java.lang.StackOverflowError
	at sun.reflect.GeneratedMethodAccessor223.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:84)
	at com.xxx.entity.LoanServiceInstitutionEntity_$$_jvst7df_21.toString(LoanServiceInstitutionEntity_$$_jvst7df_21.java)
	at java.lang.String.valueOf(String.java:2994)
	at java.lang.StringBuilder.append(StringBuilder.java:131)
	at java.util.AbstractCollection.toString(AbstractCollection.java:462)
	at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:510)
	at java.lang.String.valueOf(String.java:2994)
	at java.lang.StringBuilder.append(StringBuilder.java:131)
	at com.xxx.entity.CooperativeInstitutionEntity.toString(CooperativeInstitutionEntity.java:23)
	at java.lang.String.valueOf(String.java:2994)
	at java.lang.StringBuilder.append(StringBuilder.java:131)
	at com.xxx.entity.LoanServiceInstitutionEntity.toString(LoanServiceInstitutionEntity.java:24)
	at sun.reflect.GeneratedMethodAccessor223.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:84)
	at com.xxx.entity.LoanServiceInstitutionEntity_$$_jvst7df_21.toString(LoanServiceInstitutionEntity_$$_jvst7df_21.java)

第一眼就看到了JavassistLazyInitializer以为是懒加载问题，后来想懒加载也不会StackOverflowError啊。

再仔细看发现调用有点问题:

LoanServiceInstitutionEntity.toString()

    ->CooperativeInstitutionEntity.toString()

        ->LoanServiceInstitutionEntity.toString()

            ->CooperativeInstitutionEntity.toString()

            ....

这两个实体类循环toString()陷入死循环了，可是我只调用了一次LoanServiceInstitutionEntity.toString()。

点到这两实体类看发现他们相互关联了，代码如下：

@Data
@Entity
@DynamicInsert
@DynamicUpdate
@Table(name = \"t_cooperative_institution\")
public class CooperativeInstitutionEntity implements Cloneable, Serializable {
    @OneToMany(mappedBy = \"cooperativeInstitutionEntity\", cascade = { CascadeType.ALL }, fetch = FetchType.LAZY)
    private List<LoanServiceInstitutionEntity> loanServiceInstitutionEntityList = new ArrayList<>();
...
}


@Data
@Entity
@DynamicInsert
@DynamicUpdate
@Table(name = \"t_loan_service_institution\"})
public class LoanServiceInstitutionEntity implements Cloneable, Serializable {
    @ManyToOne(optional = false, fetch = FetchType.LAZY)
    @JoinColumn(name = \"cooperative_institution_id\", insertable = false, updatable = false, foreignKey = @ForeignKey(name = \"null\", value = ConstraintMode.NO_CONSTRAINT))
    private CooperativeInstitutionEntity cooperativeInstitutionEntity;
...
}

然后lombok的@Data注解会自动生成包含所有非静态字段的toString()方法。

所以调用LoanServiceInstitutionEntity的toString()方法会去get cooperativeInstitutionEntity属性，

然后促发hibernate懒加载机制去数据库查询数据返回cooperativeInstitutionEntity，

接着在调用cooperativeInstitutionEntity.toString()时又去get 里面的loanServiceInstitutionEntityList属性...

因为两边数据有关联，所以会无限循环下去。

解决方案：给不需要加到toString的熟悉加上@ToString.Exclude注解或者@ToString(exclude = {\"需要排除的属性名\"})