Unable to evaluate the expression Method threw 'java.lang.StackOverflowError' exception. with nested relations between entities

Question

I am fighting trough one day with one problem. So Lets get started. I have 3 classes like tags, offers and animals

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(name = "animals")
public class Animal {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "animal_id")
private Long id;

@Column(name = "name")
@NotNull
private String name;

@Column(name = "description")
@NotNull
private String text;

@Column(name = "quantity")
@NotNull
private int count;


@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "user_id", nullable = false)
private User user;

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "tag_id", nullable = false)
private Tag tags;


@OneToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "offer_id", nullable = true)
private Offer offer;

Offers

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(name = "offer")
public class    Offer {


@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "offer_id")
private Long id;

@Column(name = "title")
@NotNull
private String title;

@Column(name = "description")
@NotNull
private String text;


@Column(name = "price")
@NotNull
private int price;

@Column(name = "contact")
@NotNull
private int contact;

@Temporal(TemporalType.TIMESTAMP)
@Column(name = "create_date", nullable = false, updatable = false)
@CreationTimestamp
private java.util.Date createDate;



@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "user_id", nullable = false)
private User user;


@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "tag_id", nullable = false)
private Tag tags;


@OneToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "animal_id", nullable = false)
private Animal animal;

And tags.

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(name = "tags")
public class Tag {


@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "tag_id")
private long id;

@Column(name = "name")
@Email(message = "*Please provide a valid tag")
@NotEmpty(message = "*Please provide an tag")
private String name;


@OneToMany(mappedBy = "tags")
private Set<Offer> offers;

@OneToMany(mappedBy = "tags")
private Set<Animal> animals;

OneToOne relation is because I want to have one offer for one animal.

I have also controller like showed to add new offer.

@RequestMapping(value = "/postForm", method = RequestMethod.GET)
public String newOffer(Principal principal,Model model) {

  String e_mail = principal.getName();
  System.out.println(e_mail);
  User user = userService.findUserByEmail(e_mail);

  Offer offer = new Offer();
  offer.setUser(user);
    Long id = user.getId();

    List<Tag> tags =  tagService.findAlltags();


   List<Animal> animal = animalRepository.findAnimalByUser(user);

    model.addAttribute("tags", tags);
    model.addAttribute("animals",animal);
    model.addAttribute("offer", offer);

        return "/postForm";
}

I am passing lists like animal, and tags to pick tag, and animal assigned to the user. My animal repository.

public interface AnimalRepository extends JpaRepository<Animal, Long> {


    List<Animal> findAnimalByUser(User user);


}

And actually I have the problem with showing animals correctly. Tags are showing correctly, but animals lists cannot evaluate tags inside class of animals. To be more specific let me show You screen of traceback from Inteliji

link for imgur enter link description here Probably there is something wrong with relations but what exactly ? Thanks for all answers. :)

Answer 1

toString() method in Animal class causes this problem. Method builds return string alternately from Animal and Tag classes both have reference to each other which produces infinite process.

Get rid of @Data annotation (which includes @ToString annotation), and make your own implementation of toString() method.