How does Lombok handle @ToString with circular references?

Lombok's @ToString doesn't have built-in circular reference detection — if class A has a @ToString-included field pointing to class B, and B has a field pointing back to A, calling toString() on either one recurses infinitely (A's toString calls B's toString, which calls A's toString, and so on) until it overflows the stack with a StackOverflowError.

@ToString
public class Parent {
    private List<Child> children;   //  danger: each Child references parent back
}

@ToString
public class Child {
    @ToString.Exclude   //  break the cycle here
    private Parent parent;
    private String name;
}

The standard fix is exactly what's shown above: use @ToString.Exclude on whichever side of the bidirectional relationship you don't need printed — typically the "back-reference" side (child pointing to parent) — so the generated toString() never actually walks the cycle in the first place.

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