Spring Expected ':' instead of 't' error when returning List?

This Problem is because of infinite recursion between entity classes use @JsonIgnore for older versions and this code for newer versions.

 @OneToMany(
            mappedBy = "queue_group",fetch = FetchType.LAZY,
            cascade = CascadeType.ALL
        )
    @JsonManagedReference
    private Set<Queue> queues;

@ManyToOne(cascade=CascadeType.ALL)
        @JoinColumn(name = "qid")
       // @JsonIgnore
        @JsonBackReference
        private Queue_group queue_group;

@JsonManagedReference
private Set<HolidayDates> holidayDates;

and

@JsonBackReference
private User user;

You have an infinite recursion going on during serialization since User refers to HolidayDates and HolidayDates refer to User. You can stop it by adding @JsonIgnore to getUser in HolidayDates.