好的,所以我正在尝试使用 jackson 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
}
需要这些标签以避免序列化异常。 当我尝试序列化一个对象(无论是在文件上还是在简单的字符串上)时,一切正常。但是,当我尝试反序列化该对象时,它会引发异常。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?我该如何修复它?我还需要其他注释吗?
最佳答案
实际上,问题似乎出在“id”属性上。由于两个不同实体的属性名称相同,因此在反序列化期间会出现一些问题。不知道这是否有意义,但我解决了将 ParentEntity 的 JsonIdentityInfo
标记更改为
@JsonIdentityInfo(generator=ObjectIdGenerators.PropertyGenerator.class, property = "id", scope = ParentEntity.class))
当然,我还用 scope=ChildEntity.class 更改了 ChildEntity 的范围
按照建议here
顺便说一句,我愿意接受新的答案和建议。
关于java - Jackson - 循环依赖导致反序列化失败,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/26698434/