Issue with StackOverflowError in Spring Boot application during DTO serialization

Question

I am encountering a StackOverflowError in my Spring Boot application when attempting to serialize a DTO class (NodeAttributesDTO) that has a self-referencing relationship. The error occurs during the execution of the toString method in the DTO class.

NodeAttributes.java:

// Relevant parts of NodeAttributes.java
@OneToMany(mappedBy = "parent")
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
@JsonIgnoreProperties(value = { "children", "parent", "node" }, allowSetters = true)
private Set<NodeAttributes> children ;

@ManyToOne
@JsonIgnoreProperties(value = { "children", "parent", "node" }, allowSetters = true)
private NodeAttributes parent;

// Other fields, getters, setters, etc.

NodeAttributesDTO.java:

// Relevant parts of NodeAttributesDTO.java
private Set<NodeAttributesDTO> children;
private NodeAttributesDTO parent;

// Getters, setters, and other methods...

@Override
public String toString() {
    return "NodeAttributesDTO{" +
        "id=" + getId() +
        // Other fields...
        ", parent=" + getParent() +
        ", children=" + getChildren() +
        ", node=" + getNode() +
        "}";
}

PostMapping Request Body:

{
  // Some other fields...
  "children": [
    {
      "key": "attribute412w",
      "value": "value3",
      "valueType": "Integer",
      "type": "RESPONSE",
      "required": false,
      "enabled": true,
      "node": {
        "id": 26030
      }
    }
  ],
  // Other fields...
}

Error:

{
    "type": "https://www.jhipster.tech/problem/problem-with-message",
    "title": "Internal Server Error",
    "status": 500,
    "detail": "Handler dispatch failed; nested exception is java.lang.StackOverflowError",
    "path": "/api/node-attributes",
    "message": "error.http.500"
}

Questions:

1. How can I modify the toString method in my NodeAttributesDTO class to avoid the StackOverflowError during serialization?
2. Are there specific Jackson annotations or configurations that I should consider for handling self-referencing relationships in DTOs?

Environment: Spring Boot version: 2.7.2 Java version: 17 Database: Postgresql

I've tried:

• different Jackson annotations (@JsonManagedReference, @JsonBackReference)

Answer 1

I believe your confusion is that toString does not control the marshalling in Spring Boot.

If you were to log that object to say standard error by System.err.println() it would use that toString.

It also seems that really your toString his essentially trying to be a recursive dump of the data, but isnt' correct. I think that's just basic Java/CS.

In the toString, you could just print the current node's data, and then call toString (delagate) on all the child nodes. That should do it. You don't need the back reference in general I would think (for toString) because you would start at the top of the 'tree'.

The marshaller inspects the object and uses reflection to compose the serialized representation. It will obey certain annotations, as you note. Such as @JsonIgnore.

See this : How could I ignore a field in json response?

There's a bunch of good info here: https://www.baeldung.com/jackson

It also might help to create a simple web service outside of a code generation tool (like jhipster) to get the zen on what happens under the hood to better control generation.