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I'm having and issue with the Circular reference.

I have Rest Webservices which returns objects to the front end, the issue is when I try to return objects that have several references so as the result I get an infinite response, which generate 

java.lang.IllegalStateException: 
    Cannot call sendError() after the response has been committed

The objects are generated automatically by Hibernate Code Generation and I need to have the circular reference in the backend, I've just need to remove it before send the information to the frontend using Jackson.

The controller method header is:

@RequestMapping(value="/list", method=RequestMethod.POST)
public @ResponseBody eventResponse list(@RequestBody String sessionID) {

I'm not doing anything explicite to convert to Json, I'm a newby with this and I think that jackson resolved this automatically.

Konstantin Yovkov
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Faabass
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3 Answers3

49

There are two ways you can go about this. If you must expose your entity to the outside world, I recommend adding @JsonIgnore on the property that is causing the circular reference. This will tell Jackson not to serialize that property.

Another way is to use the bidirectional features provided by Jackson. You can either use @JsonManagedReference or @JsonBackReference. @JsonManagedReference is the "forward" part of the property and it will get serialized normally. @JsonBackReference is the "back" part of the reference; it will not be serialized, but will be reconstructed when the "forward" type is deserialized.

You can check out the examples here.

This addresses your comment: I think what you might want to do in this case is use a DTO that is visible to the outside world. I like this approach because I don't want to expose my entities to the outside. This means that the Jackson annotations would be on the DTO and not on the enity. You would need some sort of mapper or converter that converts the entity to the DTO. Now when you make changes to your entity, they won't get propagated to the DTO unless you modify your mapper/converter. I think this is ok, because when you make a change to your entity you can decide if you want that change to be exposed or not.

UPDATE

There is a good blog post here that goes into detail about the various ways you can handle bidirectional relationships in Jackson. It describes solutions that use @JsonIgnore, @JsonManagedReference and @JsonBackReference, @JsonIdentityInfo, @JsonView and a custom serializer as well. It's a pretty comprehensive writeup of the various techniques that you can use.

senerh
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Vivin Paliath
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  • Yes, I read about this. But the thing is that I don't want to "touch" the entities generated by Hibernate. Because the database keep growing so any time that I would add anything I will need to modify again all the entities. As per I understood, I have to modified the entities for both options, right? – Faabass Jun 30 '13 at 19:28
  • Is it ok if I use @JsonManagedReference and @JsonBackReference? – Mahesh Vemula Jul 28 '20 at 11:59
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    I was leery of the idea of duplicating entity structure for DTOs, but you present a good argument in favor; that extra layer of abstraction frees up internal refactoring without affecting clients. – Sam Barnum Mar 20 '22 at 15:07
10

A single annotation @JsonIdentityInfo solves the problem. It handles circular references also.Reference

pavan
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    the only problem is when you identity field is null. then you are back to square 1 - circular reference. – anton1980 Feb 17 '17 at 21:26
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    This answer doesn't indicate whether this annotation goes in the parent class or the child class. The answer could be greatly improved by indicating this information. – Michael Jan 11 '21 at 16:48
0

A @JsonbTransient solved my problem to handel circular references:

@JsonbTransient // javax.json.bind.annotation.JsonbTransient
@ManyToOne
@JoinColumn(name = "userId", referencedColumnName = "id", nullable = false)
public AContainedEntity getAContainedEntity() {
       return aContainedEntity;
}
Csongi77
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