Jackson-反序列化在循环依赖项上失败

Question

好的，所以我想用杰克逊json转换器测试一些东西。我正在尝试模拟图形行为，所以这些是我的POJO实体

@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
public class ParentEntity implements java.io.Serializable
{   
    private String id;
    private String description;
    private ParentEntity parentEntity;
    private List<ParentEntity> parentEntities = new ArrayList<ParentEntity>(0);
    private List<ChildEntity> children = new ArrayList<ChildEntity>(0);
    // ... getters and setters
}

@JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
public class ChildEntity implements java.io.Serializable
{
    private String id;
    private String description;
    private ParentEntity parent;
    // ... getters and setters
}

标签是必需的，以避免序列化时出现异常。当我尝试序列化一个对象（在文件或简单字符串上）时，一切正常。但是，当我尝试反序列化对象时，它将引发异常。这是简单的测试方法（为简单起见，省略了try
/ catch）

{
    // create some entities, assigning them some values
    ParentEntity pe = new ParentEntity();
    pe.setId("1");
    pe.setDescription("first parent");

    ChildEntity ce1 = new ChildEntity();
    ce1.setId("1");
    ce1.setDescription("first child");
    ce1.setParent(pe);

    ChildEntity ce2 = new ChildEntity();
    ce2.setId("2");
    ce2.setDescription("second child");
    ce2.setParent(pe);

    pe.getChildren().add(ce1);
    pe.getChildren().add(ce2);

    ParentEntity pe2 = new ParentEntity();
    pe2.setId("2");
    pe2.setDescription("second parent");
    pe2.setParentEntity(pe);
    pe.getParentEntities().add(pe2);

    // serialization
    ObjectMapper mapper = new ObjectMapper();
    File f = new File("parent_entity.json");
    // write to file
        mapper.writeValue(f, pe);
    // write to string
    String s = mapper.writeValueAsString(pe);
    // deserialization
    // read from file
    ParentEntity pe3 = mapper.readValue(f,ParentEntity.class);
    // read from string
    ParentEntity pe4 = mapper.readValue(s, ParentEntity.class);         
}

这是抛出的异常（当然，重复两次）

com.fasterxml.jackson.databind.JsonMappingException: Already had POJO for id (java.lang.String) [com.fasterxml.jackson.annotation.ObjectIdGenerator$IdKey@3372bb3f] (through reference chain: ParentEntity["children"]->java.util.ArrayList[0]->ChildEntity["id"])
...stacktrace...
Caused by: java.lang.IllegalStateException: Already had POJO for id (java.lang.String) [com.fasterxml.jackson.annotation.ObjectIdGenerator$IdKey@3372bb3f]
...stacktrace...

那么，问题的原因是什么呢？我该如何解决？我还需要其他注释吗？

Answer 1

实际上，似乎问题出在“
id”属性上。由于两个不同实体的属性名称相同，因此在反序列化过程中会出现一些问题。根本不知道是否有意义，但是我解决了将JsonIdentityInfoParentEntity
的标签更改为

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

当然，我也scope=ChildEntity.class
按照此处的建议更改了ChildEntity的范围

顺便说一下，我愿意接受新的答案和建议。