Problem while print OnetoMany Reletionship

Question

I'm tryng to print the object that I get from the database but everytime it give me the StackOverFlowError:

    SLF4J: Failed toString() invocation on an object of type [java.util.ArrayList]
Reported exception:
java.lang.StackOverflowError
    at java.base/java.lang.StringBuilder.<init>(StringBuilder.java:102)
    at com.example.NetflixProve.model.Tracker.toString(Tracker.java:116)
    at java.base/java.lang.String.valueOf(String.java:4215)
    at java.base/java.lang.StringBuilder.append(StringBuilder.java:169)
    at com.example.NetflixProve.model.Channel.toString(Channel.java:33)
    at java.base/java.lang.String.valueOf(String.java:4215)
    at java.base/java.lang.StringBuilder.append(StringBuilder.java:169)
    at java.base/java.util.AbstractCollection.toString(AbstractCollection.java:457)
    at org.hibernate.collection.internal.PersistentBag.toString(PersistentBag.java:622)
    at java.base/java.lang.String.valueOf(String.java:4215)
....

same even if I use System.out.println();

I deleted @Data and added @JsonBackedReference but it didn't work. My code in entities are:

@Entity
@Table(name= "TBL_CHANNEL")
@Getter
@Setter

public class Channel {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Generated(GenerationTime.ALWAYS)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "channels")
    @JsonBackReference
    private Tracker tracker;
    @Column(name = "Channel_Name")
    private String channelName;

    @Override
    public String toString() {
        return "Channel{" +
                "id=" + id +
                ", tracker=" + tracker +
                ", channelName='" + channelName + '\'' +
                '}';
    }
}

and:

@Entity
@Table(name = "TBL_TRACKER")
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class Tracker {
    @Id
    @Column(name = "ARCHIVE_ID")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Generated(GenerationTime.ALWAYS)
    private Long archiveId;

    @Column(name = "NOTIFICATION_ID")
    private String notificationId;

    @Column(name = "NOTIFICATION_ID_INDEX")
    private String notificationIdIndex;

    @Column(name = "DELIVERY_CHANNEL")
    @Enumerated(EnumType.STRING)
    private DeliveryChannel deliveryChannel;

    @Column(name = "SENDING_DATE")
    @DateTimeFormat
    private Date sendingDate;

    @Column(name = "SERVICE_ID")
    private String serviceId;

    @Column(name = "IDENTIFIER_TYPE")
    @Enumerated(EnumType.STRING)
    private IdentifierType identifierType;

    @Column(name = "IDENTIFIER")
    private String identifier;//fiscalCode

    @Column(name = "PAN")
    private String pan;


    @Column(name = "FLAG")
    @Enumerated(EnumType.STRING)
    private FlagEnum flag;

    @Column(name = "NOTIFICATION_CATEGORY")
    @Enumerated(EnumType.STRING)
    private NotificationCategory notificationCategory;

    @Column(name = "EXPIRING_DATE")
    @DateTimeFormat
    private Date expiringDate;

    @Column(name = "CREATION_DATE")
    @DateTimeFormat
    @CreationTimestamp
    private Date creationDate;

    @Column(name = "VISUALIZATION_DATE")
    @DateTimeFormat
    private Date visualizationDate;

    @Column(name = "EXPIRE_VISUALIZATION_DATE")
    @DateTimeFormat
    private Date expireVisualizationDate;


    @Column(name = "portal")
    private PortalEnum portalEnum;

    @Column(name = "campaign_name")
    private String campaignName;

    @Column(name = "business_priority")
    private int businessPriority;

    @OneToMany(cascade = {CascadeType.ALL},mappedBy = "tracker")
       @JsonManagedReference
    private List<Channel> channelsId;



    @Override
    public String toString() {
        return "Tracker{" +
                "archiveId=" + archiveId +
                ", notificationId='" + notificationId + '\'' +
                ", notificationIdIndex='" + notificationIdIndex + '\'' +
                ", deliveryChannel=" + deliveryChannel +
                ", sendingDate=" + sendingDate +
                ", serviceId='" + serviceId + '\'' +
                ", identifierType=" + identifierType +
                ", identifier='" + identifier + '\'' +
                ", pan='" + pan + '\'' +
                ", flag=" + flag +
                ", notificationCategory=" + notificationCategory +
                ", expiringDate=" + expiringDate +
                ", creationDate=" + creationDate +
                ", visualizationDate=" + visualizationDate +
                ", expireVisualizationDate=" + expireVisualizationDate +
                ", portalEnum=" + portalEnum +
                ", campaignName='" + campaignName + '\'' +
                ", businessPriority=" + businessPriority +
                ", channelsId=" + channelsId +
                '}';
    }

The error happen here, when I'm trying to get the code, (later I will use the DTO to print)

public List<Tracker> findAll(){
    List<Tracker> trackerList= trackerRepo.findAll();
    log.info("tracker: {}",trackerList);
    return trackerList;
}

Answer 1

You can use @Data, just add @ToString.Exclude to the tracker member of Channel. The point is to not have any circular paths while invoking toString.