Why JPA OneToMany mapping findAll method returned recursive object?

I have 2 domain classes, PO class and Product Class, and there is a List inside PO class. So Product is ManyToOne to PO, and PO is OneToMany to Product.

public class PO {
    ....

    @OneToMany(mappedBy = "po", cascade= CascadeType.ALL, orphanRemoval=true)
    private List<Product> products = new ArrayList<>();
    .....
}

public class Product {
    ....
    @ManyToOne(optional = false)
    @JoinColumn(name = "po_id")
    private PO po;
    ....
}

And when building the po object. I set the po field in Product with the reference of po.

PO repo = new PO();
....
for (StockLine item: source.getStockLines()) {
    Product prod = new Product();
    ....
    prod.setPo(repo);
    repo.getProducts().add(prod);
}

when I call PORepo.save(po); it's working, foreign key is filled and all data in both tables are correct.

But the problem is when I fetch the PO using PORepo.findAll(), I debugged and found the object is actually recursively reference itself.

Is this normal? I don't think it's normal, but where I have done wrong?

btw, if I don't add @JsonManagedReference and @JsonBackReference the generated json will be in recursive format too. The json issue can be fixed by above to annotations, but how to fix the returned object issue? I am using spring boot data jpa 1.5.6.RELEASE