如何在循环引用中使用@JsonIdentityInfo？

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

我正在尝试使用Jackson 2中的@JsonIdentityInfo,如此处所述。

For testing purposes I created the following two classes:

出于测试目的,我创建了以下两个类:

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:

当然,天真的方法很糟糕:

@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 *Error
    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.

将@JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class,property =“@ id”)添加到A类和/或B类也不起作用。

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

我希望我可以序列化(以后反序列化)a到这样的东西:(虽然不太确定JSON)

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

How can I do that?

我怎样才能做到这一点?

3 个解决方案

#1

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

看来jackson-jr有Jackson的一部分功能。 @JsonIdentityInfo一定不能削减。

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

如果您可以使用完整的Jackson库,只需使用标准的ObjectMapper和您在问题中建议的@JsonIdentityInfo注释,并序列化您的对象。例如

@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.

嵌套a通过其@id引用根对象的位置。

#2

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.

有几种方法可以解决此循环引用或无限递归问题。这个链接详细解释了每一个。我已经解决了我的问题,包括每个相关实体上面的@JsonIdentityInfo注释,尽管@JsonView是最新的,根据你的风景,它可能是一个更好的解决方案。

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

Or using an IntSequenceGenerator implementation:

或者使用IntSequenceGenerator实现:

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

#3

-1

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

在某些情况下,可能需要使用@JsonProperty(“id”)注释Id属性

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

例如,在我的情况下,这使我的应用程序正确运行。

#1