如何在自定义反序列化器中使用jackson ObjectMapper？

Question

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.ObjectCodec;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonNode;
import com.mypackage.MyInterface;
import com.mypackage.MyFailure;
import com.mypackage.MySuccess;

import java.io.IOException;

public class MyDeserializer extends JsonDeserializer<MyInterface> {

    @Override
    public MyInterface deserialize(JsonParser jp, DeserializationContext ctxt)
            throws IOException, JsonProcessingException {
        ObjectCodec codec = jp.getCodec();
        JsonNode node = codec.readTree(jp);
        if (node.has("custom_field")) {
            return codec.treeToValue(node, MyFailure.class);
        } else {
            return codec.treeToValue(node, MySuccess.class);
        }
    }
}

public class MyFailure implements MyInterface {}

public class MySuccess implements MyInterface {}

@JsonDeserialize(using = MyDeserializer.class)
public interface MyInterface {}

我得到了StackOverflowError。了解codec.treeTovalue调用相同的反序列化器。是否有一种方法可以在custome反序列化器中使用codec.treetovalue或objectmapper.readvalue(String，class ) ？

Answer 1

直接的问题似乎是，@jsondeserialize(using=...)被用于MyInterface的实现以及MyInterface本身：因此出现了无休止的循环。

您可以在每个实现中修复此重写设置：

@JsonDeserialize(using=JsonDeserializer.None.class)
public static class MySuccess implements MyInterface {
}

或者通过使用模块而不是注释来配置反序列化（并从MyInterface中删除注释）：

mapper.registerModule(new SimpleModule() {{
    addDeserializer(MyInterface.class, new MyDeserializer());
}});

@Override
public MyInterface convert(JsonNode root, DeserializationContext ctxt) throws IOException {
    java.lang.reflect.Type targetType;
    if (root.has("custom_field")) {
        targetType = MyFailure.class;
    } else {
        targetType = MySuccess.class;
    }
    JavaType jacksonType = ctxt.getTypeFactory().constructType(targetType);
    JsonDeserializer<?> deserializer = ctxt.findRootValueDeserializer(jacksonType);
    JsonParser nodeParser = root.traverse(ctxt.getParser().getCodec());
    nodeParser.nextToken();
    return (MyInterface) deserializer.deserialize(nodeParser, ctxt);
}