How to use @JsonIdentityInfo with circular references?

Question

I am trying to use the @JsonIdentityInfo from Jackson 2 as described here.

For testing purposes I created the following two classes:

public class A
{
    private B b;
    // constructor(s) and getter/setter omitted
}
public class B
{
    private A a;
    // see above
}

Of course, the naive approach failes:

@Test
public void testJacksonJr() throws Exception
{
    A a = new A();
    B b = new B(a);
    a.setB(b);
    String s = JSON.std.asString(a);// throws StackOverflowError
    Assert.assertEquals("{\"@id\":1,\"b\":{\"@id\":2,\"a\":1}}", s);
}

Adding @JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class, property="@id") to class A and/or class B does not work either.

I was hoping that I could serialize (and later deserialize) a to something like this: (not too sure about the JSON though)

{
    "b": {
        "@id": 1,
        "a": {
            "@id": 2,
            "b": 1
        }
    }
}

How can I do that?

This works fine for me and generates `{"@id":1,"b":{"@id":2,"a":1}}`. — Sotirios Delimanolis, May 18 '16 at 14:40
Strange. I am using jackson-jr-all-2.7.4.jar and com.fasterxml.jackson.jr.ob.JSON. What JSON class have you used? With the annotation on both classes? — Burkhard, May 18 '16 at 14:46
I just created an `ObjectMapper` and use `writeValueAsString`. (This is with your `@JsonIdentityInfo` annotations.) — Sotirios Delimanolis, May 18 '16 at 14:47

Sotirios Delimanolis · Accepted Answer · 2017-09-12T14:44:04.817

24

It seems jackson-jr has a subset of Jackson's features. @JsonIdentityInfo must not have made the cut.

If you can use the full Jackson library, just use a standard ObjectMapper with the @JsonIdentityInfo annotation you suggested in your question and serialize your object. For example

@JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class, property="@id")
public class A {/* all that good stuff */}

@JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class, property="@id")
public class B {/* all that good stuff */}

and then

A a = new A();
B b = new B(a);
a.setB(b);
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writeValueAsString(a));

will generate

{
    "@id": 1,
    "b": {
        "@id": 2,
        "a": 1
    }
}

where the nested a is referring to the root object by its @id.

edited Sep 12 '17 at 14:44

answered May 18 '16 at 15:24

Sotirios Delimanolis

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@ Sotirios Delimanolis Any idea how to ignore the "@id" in the json response? – SuRa Sep 12 '17 at 11:17
1

@SuRa What do you mean by _ignore_? That's the point of `@JsonIdentityInfo`, to provide a property (it can have any name) that identifies the object. – Sotirios Delimanolis Sep 12 '17 at 14:04
While retrieving data from rest client, I am getting <> exception. How to fix this? The nested "a": 1 causing the problem. – SuRa Sep 12 '17 at 14:25
@SuRa I'm not sure about that. The `a` should be a regular property `getA` and `setA`. You'd have to provide a full example, consider asking a new question. – Sotirios Delimanolis Sep 12 '17 at 14:46
@SuRa looks like you want JsonIgnore annotation – gstackoverflow Aug 12 '21 at 12:14

Cassio Seffrin · Answer 2 · 2018-05-04T00:04:46.950

There are several approaches to solve this circular references or infinite recursion issues. This link explain in details each one. I have solved my issues including @JsonIdentityInfo annotation above each related entity, although @JsonView is more recent and may it's a better solution depending of your scenery.

@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")

Or using an IntSequenceGenerator implementation:

@JsonIdentityInfo(generator=ObjectIdGenerators.IntSequenceGenerator.class)
@Entity
public class A implements Serializable 
...

score -1 · Answer 3 · answered Feb 25 '18 at 11:06

-1

In some cases, it can be necessary to annotate the Id Property with @JsonProperty("id")

For example, in my case, this made my application run correctly.

answered Feb 25 '18 at 11:06

dalil TALEB

11

How to use @JsonIdentityInfo with circular references?

3 Answers3

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