Jackson-deserialization fails on circular dependencies(JackSon无限递归问题)

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Ok, so I'm trying to test some stuffs with jackson json converter. I'm trying to simulate a graph behaviour, so these are my POJO entities

@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
}

The tags are required in order to avoid exception on serialization. When I try to serialize an object (both on a file or on a simple string) all works fine. However, when I try to deserialize the object, it throws an exception. This is the simple test method (try/catch omitted for simplicity)

{
    // create some entities, assigning them some values
    ParentEntity pe = new ParentEntity();
    pe.setId("1");
    pe.setDescription("first parent");
</span><span class="typ">ChildEntity</span><span class="pln"> ce1 </span><span class="pun">=</span><span class="pln"> </span><span class="kwd"><span class="hljs-keyword">new</span></span><span class="pln"> </span><span class="typ">ChildEntity</span><span class="pun">();</span><span class="pln">
ce1</span><span class="pun">.</span><span class="pln">setId</span><span class="pun">(</span><span class="str"><span class="hljs-string">"1"</span></span><span class="pun">);</span><span class="pln">
ce1</span><span class="pun">.</span><span class="pln">setDescription</span><span class="pun">(</span><span class="str"><span class="hljs-string">"first child"</span></span><span class="pun">);</span><span class="pln">
ce1</span><span class="pun">.</span><span class="pln">setParent</span><span class="pun">(</span><span class="pln">pe</span><span class="pun">);</span><span class="pln">

</span><span class="typ">ChildEntity</span><span class="pln"> ce2 </span><span class="pun">=</span><span class="pln"> </span><span class="kwd"><span class="hljs-keyword">new</span></span><span class="pln"> </span><span class="typ">ChildEntity</span><span class="pun">();</span><span class="pln">
ce2</span><span class="pun">.</span><span class="pln">setId</span><span class="pun">(</span><span class="str"><span class="hljs-string">"2"</span></span><span class="pun">);</span><span class="pln">
ce2</span><span class="pun">.</span><span class="pln">setDescription</span><span class="pun">(</span><span class="str"><span class="hljs-string">"second child"</span></span><span class="pun">);</span><span class="pln">
ce2</span><span class="pun">.</span><span class="pln">setParent</span><span class="pun">(</span><span class="pln">pe</span><span class="pun">);</span><span class="pln">

pe</span><span class="pun">.</span><span class="pln">getChildren</span><span class="pun">().</span><span class="pln">add</span><span class="pun">(</span><span class="pln">ce1</span><span class="pun">);</span><span class="pln">
pe</span><span class="pun">.</span><span class="pln">getChildren</span><span class="pun">().</span><span class="pln">add</span><span class="pun">(</span><span class="pln">ce2</span><span class="pun">);</span><span class="pln">

</span><span class="typ">ParentEntity</span><span class="pln"> pe2 </span><span class="pun">=</span><span class="pln"> </span><span class="kwd"><span class="hljs-keyword">new</span></span><span class="pln"> </span><span class="typ">ParentEntity</span><span class="pun">();</span><span class="pln">
pe2</span><span class="pun">.</span><span class="pln">setId</span><span class="pun">(</span><span class="str"><span class="hljs-string">"2"</span></span><span class="pun">);</span><span class="pln">
pe2</span><span class="pun">.</span><span class="pln">setDescription</span><span class="pun">(</span><span class="str"><span class="hljs-string">"second parent"</span></span><span class="pun">);</span><span class="pln">
pe2</span><span class="pun">.</span><span class="pln">setParentEntity</span><span class="pun">(</span><span class="pln">pe</span><span class="pun">);</span><span class="pln">
pe</span><span class="pun">.</span><span class="pln">getParentEntities</span><span class="pun">().</span><span class="pln">add</span><span class="pun">(</span><span class="pln">pe2</span><span class="pun">);</span><span class="pln">

</span><span class="com"><span class="hljs-comment">// serialization</span></span><span class="pln">
</span><span class="typ">ObjectMapper</span><span class="pln"> mapper </span><span class="pun">=</span><span class="pln"> </span><span class="kwd"><span class="hljs-keyword">new</span></span><span class="pln"> </span><span class="typ">ObjectMapper</span><span class="pun">();</span><span class="pln">
</span><span class="typ">File</span><span class="pln"> f </span><span class="pun">=</span><span class="pln"> </span><span class="kwd"><span class="hljs-keyword">new</span></span><span class="pln"> </span><span class="typ">File</span><span class="pun">(</span><span class="str"><span class="hljs-string">"parent_entity.json"</span></span><span class="pun">);</span><span class="pln">
</span><span class="com"><span class="hljs-comment">// write to file</span></span><span class="pln">
    mapper</span><span class="pun">.</span><span class="pln">writeValue</span><span class="pun">(</span><span class="pln">f</span><span class="pun">,</span><span class="pln"> pe</span><span class="pun">);</span><span class="pln">
</span><span class="com"><span class="hljs-comment">// write to string</span></span><span class="pln">
</span><span class="typ">String</span><span class="pln"> s </span><span class="pun">=</span><span class="pln"> mapper</span><span class="pun">.</span><span class="pln">writeValueAsString</span><span class="pun">(</span><span class="pln">pe</span><span class="pun">);</span><span class="pln">
</span><span class="com"><span class="hljs-comment">// deserialization</span></span><span class="pln">
</span><span class="com"><span class="hljs-comment">// read from file</span></span><span class="pln">
</span><span class="typ">ParentEntity</span><span class="pln"> pe3 </span><span class="pun">=</span><span class="pln"> mapper</span><span class="pun">.</span><span class="pln">readValue</span><span class="pun">(</span><span class="pln">f</span><span class="pun">,</span><span class="typ">ParentEntity</span><span class="pun">.</span><span class="kwd">class</span><span class="pun">);</span><span class="pln">
</span><span class="com"><span class="hljs-comment">// read from string</span></span><span class="pln">
</span><span class="typ">ParentEntity</span><span class="pln"> pe4 </span><span class="pun">=</span><span class="pln"> mapper</span><span class="pun">.</span><span class="pln">readValue</span><span class="pun">(</span><span class="pln">s</span><span class="pun">,</span><span class="pln"> </span><span class="typ">ParentEntity</span><span class="pun">.</span><span class="kwd">class</span><span class="pun">);</span><span class="pln">         

}

and this is the exception thrown (of course, repeated twice)

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...

So, what is the cause of the problem? How can I fix it? Do I need some other annotation?

Jackson-deserialization fails on circular dependencies(JackSon无限递归问题)

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