使用基于JSON类型的Jackson进行反序列化

Question

I have a JSON payload I am attempting to deserialize using Jackson that looks like:

{
  "id": "12",
  "type": "foo",
  "created": "2011-03-20T31:12:00+00:00",
  "data": {
    "object": {
        objectId: 1
        fizz: "bizz"
    }
}

There are 3 different "type" responses possible {foo, bar, foobar} and, depending on which type is in the payload, the "object" node will have different data underneath it (type foo has fizz for example). I am attempting to write some deserializers that will detect the type, and output a class containing the contents of "object" . I can basically ignore the id and created fields. The types of classes are as follows:

public interface ObjectType {
   String getId()
}

public class Foo implements ObjectType {
   String objectId;
   String fizz;

   String getId() {
      return objectId;
   }
}

public class Bar implements ObjectType {
   String objectId;
   String test;

   String getId() {
      return objectId;
   }
}

public class FooBar implements ObjectType {
   String objectId;
   String something;

   String getId() {
      return objectId;
   }
}

What is the simplest way to do so in Jackson?

Answer 1

One possibility is to write a custom deserializer. A stub implementation could be as follows:

class ContainerDeserializer extends StdDeserializer<Container> {

    private static final long serialVersionUID = 8976140492203602443L;

    public ContainerDeserializer() {
        this(null);
    }

    public ContainerDeserializer(Class<?> vc) {
        super(vc);
    }

    @Override
    public Container deserialize(JsonParser jp, DeserializationContext ctxt)
            throws IOException, JsonProcessingException {
        JsonNode node = jp.getCodec().readTree(jp);
        int id = (Integer) ((IntNode) node.get("id")).numberValue();
        String type = node.get("type").asText();
        ObjectType obj;
        String objId = node.get("obj").get("objectId").asText();
        switch (type) {
        case "foo":
            String fizz = node.get("obj").get("fizz").asText();
            obj = new Foo(objId, fizz);
            break;
        case "bar":
            String test = node.get("obj").get("test").asText();
            obj = new Bar(objId, test);
            break;
        default:
            // Error handling
            obj = null;

        }

        return new Container(id, type, obj);
    }
}

For the implementation I assumed you have the following Container class:

class Container {
    private String type;
    private int id;
    private ObjectType obj;

    public Container(int id, String type, ObjectType obj) {
        this.id = id;
        this.type = type;
        this.obj = obj;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public ObjectType getObj() {
        return obj;
    }

    public void setObj(ObjectType obj) {
        this.obj = obj;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

}

I also added getters and setters to your Foo and Bar classes.

Now just register the Deserializer with

ObjectMapper om = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Container.class, new ContainerDeserializer());
om.registerModule(module);

and deserialize using

om.readValue(test, Container.class);