On Wed, Sep 25, 2019 at 12:35 AM Marc Dzaebel <[email protected]> wrote:
>
> Hi Tatu,
>
> Using only ObjectMapper#enableDefaultTyping() does not serialize into a
> polymorphic Json-String
> Using only ObjectMapper#enableDefaultTyping() does not deserialize a
> polymorphic Json-String --> error
> Unexpected token (START_OBJECT), expected START_ARRAY: need JSON Array to
> contain As.WRAPPER_ARRAY type information for class java.lang.Object
>
> So the question remains. How to serialize/deserialize an Object
> polymorphically.
>
> Here is the code, that demonstrates the problem:
>
> import java.io.IOException;
> import com.fasterxml.jackson.annotation.JsonTypeInfo;
> import com.fasterxml.jackson.databind.JavaType;
> import com.fasterxml.jackson.databind.ObjectMapper;
> import com.fasterxml.jackson.databind.ObjectMapper.DefaultTypeResolverBuilder;
> import com.fasterxml.jackson.databind.ObjectMapper.DefaultTyping;
>
> public class MapValues2 {
> public static void main(String[] args) throws IOException,
> ClassNotFoundException {
> final ObjectMapper serializer = new ObjectMapper(), deserializer =
> new ObjectMapper();
> DefaultTypeResolverBuilder typeResolver = new
> DefaultTypeResolverBuilder(DefaultTyping.NON_FINAL) {
> @Override public boolean useForType(JavaType t) {
> return Throwable.class.isAssignableFrom(t.getRawClass());
> }};
> typeResolver.init(JsonTypeInfo.Id.CLASS, null);
> typeResolver.inclusion(JsonTypeInfo.As.PROPERTY);
^^^ why?
What is the purpose of custom TypeResolverBuilder here?
Especially one that ONLY adds type information for something declared
as `Throwable`.
No, this should not work the way code expects here.
Just use existing criteria.
> serializer.setDefaultTyping(typeResolver);
> deserializer.enableDefaultTyping();
> String polyJson = serializer.writeValueAsString(new Exception());
> System.out.println("Excpetion:\n" + polyJson);
> System.out.println("1: Read poly:" + deserializer.readValue(polyJson,
> Object.class).getClass()); // error
> }
> }
>
> Exception in thread "main"
> com.fasterxml.jackson.databind.exc.MismatchedInputException: Unexpected token
> (START_OBJECT), expected START_ARRAY: need JSON Array to contain
> As.WRAPPER_ARRAY type information for class java.lang.Object
> at [Source:
> (String)"{"@class":"java.lang.Exception","cause":null,"stackTrace":["[Ljava.lang.StackTraceElement;",[{"@class":"java.lang.StackTraceElement","methodName":"main","fileName":"MapValues2.java","lineNumber":25,"className":
> ...
Now: while I am not sure I fully understand the question here, there
IS one important fix, included in 2.10.0.pr3:
https://github.com/FasterXML/jackson-databind/issues/1093
which should now support use of `Object.class` as the target type WITH
polymorphic deserialization.
So you may want to try your original code with 2.10.0.pr3. Same fix
will be in 2.10.0.
It would have prevented earlier usage.
-+ Tatu +-
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