There is a cycle in the hierarchy!" json

I am getting one JSON exception called "net.sf.json.JSONException: There is a cycle in the hierarchy!"

here is code

Query q = em.createQuery("SELECT e from employee e ");
List<Employee> employeeList = q.getResultList();
JSONObject response = new JSONObject();
response.put("empList", employeeList);


here is Employee Entity. it has one to many relation

public class Employee {
@Id
private String userId;
@JoinColumn(name = "T_MENTORS_userId", referencedColumnName = "userId")
private Collection<Experience> experience;
}


3 Answers
3

You may be running into a circular reference. Does Experience refer to Employee and Employee refers to Experience?

Experience

Employee

Employee

Experience

If so, there is a couple of solutions:

Employee

Experience

Employee

Experience

Employee

See Martin Fowler for an overview of DTO:

http://martinfowler.com/eaaCatalog/dataTransferObject.html

In this situation, according to your business logic, you can delete one of reference, for example :

Employee{

private Collection<Experience> experiences;
}


and in Experience

Experience
{
// no reference to Employee
}


If you don't want to remove the reference from the entity, there is a workaround.
Use,

JSONObject response = new JSONObject();
response.getJsonConfig().
setCycleDetectionStrategy(CycleDetectionStrategy.LENIENT)
response.put("empList", employeeList);


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