Solved – StackOverflowError in JPA @ManyToMany Mapping with @Data Annotation

The java.lang.StackOverflowError occurs when there is an infinite recursion or circular reference in your object mappings. In the case of a @ManyToMany mapping in JPA with the @Data annotation, the StackOverflowError can occur due to the bidirectional relationship between entities. This causes an infinite loop during serialization or when accessing certain properties.

Today, one of our fresher team asked me about this error and I found that she has used @Data annotation from the Lombok project.

To fix the java.lang.StackOverflowError while using @ManyToMany mapping in JPA with @Data annotation, you can try the following approaches:

1. Break the Circular Reference

• One common cause of the StackOverflowError is a circular reference between the entities involved in the @ManyToMany relationship.
• To break the circular reference, you can mark one side of the relationship with the @JsonIgnore annotation (from com.fasterxml.jackson.annotation package) to exclude it from serialization and avoid the infinite loop.
• For example, consider two entities EntityA and EntityB with a @ManyToMany relationship:

@Entity
public class EntityA {
    // Other fields and annotations

    @ManyToMany
    @JsonIgnore
    private List<EntityB> entityBs;
    
    // Getters and setters
}

@Entity
public class EntityB {
    // Other fields and annotations

    @ManyToMany(mappedBy = "entityBs")
    private List<EntityA> entityAs;

    // Getters and setters
}

In this example, the @JsonIgnore annotation is applied to the entityBs field in EntityA, which prevents it from being serialized and avoids the circular reference.

2. Use @ToString.Exclude

• If you are using the Lombok @Data annotation to generate getters, setters, equals(), hashCode(), and toString() methods, you can use the @ToString.Exclude annotation to exclude the problematic fields from the toString() method generation.
• By excluding the fields causing the circular reference from the generated toString() method, you can prevent the StackOverflowError during serialization.

@Entity
@Data
public class EntityA {
    // Other fields and annotations

    @ManyToMany
    @ToString.Exclude
    private List<EntityB> entityBs;
}

@Entity
@Data
public class EntityB {
    // Other fields and annotations

    @ManyToMany(mappedBy = "entityBs")
    @ToString.Exclude
    private List<EntityA> entityAs;
}

3. Use a DTO (Data Transfer Object)

• If the circular reference cannot be easily broken or excluded, you can create a separate DTO class to represent the data without the circular reference.
• The DTO class should have only the necessary fields and exclude the circular reference properties.
• Convert the entities to DTOs before serialization and use the DTOs for serialization.
• This approach provides more control over the serialization process and allows you to tailor the data specifically for the serialization needs.

By applying one of these approaches, you should be able to fix the java.lang.StackOverflowError caused by circular references in the @ManyToMany mapping when using the @Data annotation.

Do you know how I solved the problem I’ve mentioned above?

I just ask her to use the annotation @ToString.Exclude in the field that was causing the issue and the problem was solved.

In this post, I’ve mentioned the three best methods to solve the java.lang.StackOverflowError caused by circular references in the @ManyToMany mapping when using the @Data annotation. You can use one of them to solve your error.

Cheers!