杰克逊将json属性反序列化为对象

Question

I need to deserialize the following json:

{
    //...
    "foo_id":1
    //...
}

Into an object of class Foo with its id property set to the foo_id json property.

I need to do this within a custom deserializer. What is the most easy way to accomplish this?

I was thinking to somehow "transform" the json to

{
    //...
    "foo_id":{
        "id":1
    }
    //...
}

and then delegate this back to Jackson.

In this case, the object is of type Foo, but there are others which might not be of this class. Also, in this case, that json is a number, but I would like to support if it was a string as well. So, I need a kind of generic way to do this, that's why I think delegating back to Jackson might be a good idea.

No annotations allowed. Suppose you're already writing the Deserializer for this property.

Answer 1

Take a look at this . Here is a code that I think might help you to get some ideas.

public class MyDeserializer extends JsonDeserializer< Message >
{
@Override
public Message deserialize( JsonParser jp, DeserializationContext arg1 ) throws IOException,
        JsonProcessingException
{
    ObjectMapper mapper = (ObjectMapper) jp.getCodec();  
    ObjectNode root = (ObjectNode) mapper.readTree(jp);  
    Class<? extends Message> subClass = null;  
    Iterator<Entry<String, JsonNode>> elementsIterator = root.getFields();  
    while (elementsIterator.hasNext())  
    {  
      Entry<String, JsonNode> element = elementsIterator.next();  
      String name = element.getKey();  
      if ("foo_id".equals(name))  
      {  
         if(element.getValue().isInt())
            subClass = FooInteger.Class;  
         break;  
      }  
    }  
    if (subClass == null) return null;  
    return mapper.readValue(root, subClass);    
}
}

Answer 2

Have you considered use of mix-in annotations ? With Jackson 2.2, you could also use converters to do two-step processing ( @JsonDeserialize(converter=MyConverter.class ).