使用不带注释的@JsonIdentityInfo

Question

我使用Jackson 2.2.3将POJO序列化为JSON。然后我遇到了一个问题，就是我无法序列化递归结构...我通过使用@JsonIdentityInfo=> 解决了这个问题，效果很好。

但是，我不希望此注释位于POJO的顶部。

所以我的问题是：还有其他可能性设置我的默认行为ObjectMapper以对每个POJO使用该功能吗？

所以我想转换这个注释代码

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

像

ObjectMapper om = new ObjectMapper();
om.setDefaultIdentityInfo(ObjectIdGenerators.IntSequenceGenerator.class, "@id");

有任何想法吗？

Answer 1

您可以使用Jackson混合注释或Jackson注释内省器来实现。

这是显示两种方法的示例：

public class JacksonJsonIdentityInfo {
    @JsonIdentityInfo(
            generator = ObjectIdGenerators.IntSequenceGenerator.class, property = "@id")
    static class Bean {
        public final String field;

        public Bean(final String field) {this.field = field;}
    }

    static class Bean2 {
        public final String field2;

        public Bean2(final String field2) {this.field2 = field2;}
    }

    @JsonIdentityInfo(
            generator = ObjectIdGenerators.IntSequenceGenerator.class, property = "@id2")
    static interface Bean2MixIn {
    }

    static class Bean3 {
        public final String field3;

        public Bean3(final String field3) {this.field3 = field3;}
    }

    static class MyJacksonAnnotationIntrospector extends JacksonAnnotationIntrospector {
        @Override
        public ObjectIdInfo findObjectIdInfo(final Annotated ann) {
            if (ann.getRawType() == Bean3.class) {
                return new ObjectIdInfo(
                        PropertyName.construct("@id3", null),
                        null,
                        ObjectIdGenerators.IntSequenceGenerator.class,
                        null);
            }
            return super.findObjectIdInfo(ann);
        }
    }

    public static void main(String[] args) throws JsonProcessingException {
        final Bean bean = new Bean("value");
        final Bean2 bean2 = new Bean2("value2");
        final Bean3 bean3 = new Bean3("value3");
        final ObjectMapper mapper = new ObjectMapper();
        mapper.addMixInAnnotations(Bean2.class, Bean2MixIn.class);
        mapper.setAnnotationIntrospector(new MyJacksonAnnotationIntrospector());
        System.out.println(mapper.writeValueAsString(bean));
        System.out.println(mapper.writeValueAsString(bean2));
        System.out.println(mapper.writeValueAsString(bean3));
    }    
}

输出：

{"@id":1,"field":"value"}
{"@id2":1,"field2":"value2"}
{"@id3":1,"field3":"value3"}