杰克逊自我引用导致循环

问题描述

用Jackson将hibernate对象转换成JSON时有问题，因为有些对象在其定义中有一个自引用。
问题是我不控制这些实体的代码，所以我不能把注释放在那里。

其实我只想限制深度的递归性，例如5个级别。我需要与包含自引用的任何实体对象一起工作的通用代码。是否有可能？
我不介意使用另一个JSON库。

以下简单代码

  ObjectMapper mapper = new ObjectMapper（）; 
 
 Query q = session.createQuery（from Hazard）; 
列出< Hazard>危险= q.list（）; 
 
（危险h：危险）{
字符串危险Json; 
 hazardJson = mapper.writeValueAsString（h）; 
} 
  

给我例外：

 
 org.codehaus.jackson.map.JsonMappingException：直接引用循环的自引用（通过引用链：com.fgm.imsma.pojo.Hazard [location]  - > com。 fgm.imsma.pojo.Location [location]）
 at org.codehaus.jackson.map.ser.BeanPropertyWriter._reportSelfReference（BeanPropertyWriter.java:473）
 at org.codehaus.jackson.map .ser.BeanPropertyWriter.serializeAsField（BeanPropertyWriter.java:411）
 at org.codehaus.jackson.map.ser.BeanSerializer.serializeFields（BeanSerializer.java:245）
 at org.codehaus.jackson.map .ser.BeanSerializer.serialize（BeanSerializer.java:212）
 at org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField（BeanPropertyWriter.java:428）
 at org.codehaus.jackson.map .ser.BeanSerializer.serializeFields（BeanSerializer.java:245）
 at org.codehaus.jackson.map.ser.BeanSerializer.serialize（BeanSerializer.java:212）
 at org.codeh aus.jackson.map.ser.StdSerializerProvider._serializeValue（StdSerializerProvider.java:587）
 at org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue（StdSerializerProvider.java:245）
 at org。 codehaus.jackson.map.ObjectMapper._configAndWriteValue（ObjectMapper.java:1993）
在org.codehaus.jackson.map.ObjectMapper.writeValueAsString（ObjectMapper.java:1595）
在imsma.json.GetObjects。 main（GetObjects.java:47）
 
 

感谢您提出任何建议！

解决方案

使用 - 它处理循环引用（带有 @JsonIdentityInfo 注解）

如果您无法添加注释直接到类然后使用MixIn注释。这里有一个例子：

I have a problem when converting hibernate objects to JSON with Jackson, because some objects have a self-reference in their definition.The problem is that I don't control the code of those entities so I cannot put annotations in there.

Actually I would like to just limit the depth of the recursivity, for example to 5 levels. I need generic code that works with any entity object that contains self reference.. Is it possible?I don't mind use another JSON library.

The following simple code

ObjectMapper mapper = new ObjectMapper();

Query q = session.createQuery("from Hazard ");
List<Hazard> hazards = q.list();

for (Hazard h : hazards) {
    String hazardJson;
    hazardJson = mapper.writeValueAsString(h);
}

Gives me exception:

org.codehaus.jackson.map.JsonMappingException: Direct self-reference leading to cycle (through reference chain: com.fgm.imsma.pojo.Hazard["location"]->com.fgm.imsma.pojo.Location["location"])
    at org.codehaus.jackson.map.ser.BeanPropertyWriter._reportSelfReference(BeanPropertyWriter.java:473)
    at org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:411)
    at org.codehaus.jackson.map.ser.BeanSerializer.serializeFields(BeanSerializer.java:245)
    at org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:212)
    at org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:428)
    at org.codehaus.jackson.map.ser.BeanSerializer.serializeFields(BeanSerializer.java:245)
    at org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:212)
    at org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:587)
    at org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:245)
    at org.codehaus.jackson.map.ObjectMapper._configAndWriteValue(ObjectMapper.java:1993)
    at org.codehaus.jackson.map.ObjectMapper.writeValueAsString(ObjectMapper.java:1595)
    at imsma.json.GetObjects.main(GetObjects.java:47)

Thanks in advance for any suggestions!

解决方案

Use Jackson 2.0 - it handles cyclic references (with @JsonIdentityInfo annotation)

If you cannot add annotations directly to the class then use MixIn annotations. An example here: http://wiki.fasterxml.com/JacksonMixInAnnotations

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