I saw https://github.com/FasterXML/jackson-databind/issues/336 and in the
end they've repeatedly asked to take this here, so here I am. TLDR - if you
have an abstract class (or interface) with @JsonTypeInfo(...) and put a
bunch of those into a collection the type information of each element will
not be serialized when you serialize the collection (and same thing with
maps). I don't understand the reasoning given in the ticket - this is only
an issue on serialization when the implementation information is clearly
available. You have concrete implementation class of the object to
serialize since you've obviously managed to create the object. Of course
you know all of its superclasses and implemented interfaces and whatever
annotations come with those. I say again, this is only an issue on
serialization, if you write JSON for a collection with type information in
each element it will get deserialized no problem without any kind of hacks
as expected. Here's an example:
package foo;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonGetter;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
import com.fasterxml.jackson.annotation.JsonTypeInfo.Id;
import com.fasterxml.jackson.databind.ObjectMapper;
public class Test {
@JsonTypeInfo (include = As.PROPERTY, use = Id.CLASS)
public static abstract class Foo {
@Override
public String toString () {
return "." + this.getClass ().getSimpleName ();
}
//@JsonGetter ("@class")
//private String type () {
// return getClass ().getName ();
//}
}
public static class Bar extends Foo {
private @JsonProperty String lol = "lol";
}
private Map<String, Foo> foo;
private Map<String, Bar> bar;
public static void main (String[] args) throws Exception {
ObjectMapper m = new ObjectMapper ();
Foo f = new Bar ();
System.out.println ("1) " + m.writeValueAsString (f));
System.out.println ("2) " + m.readValue ("{\"@class\":\"foo.Test$Bar\"}",
Foo.class));
Object o = m.readValue ("{\"b\":{\"@class\":\"foo.Test$Bar\"}}",
m.constructType (Test.class.getDeclaredField (
"bar").getGenericType ()));
o = m.readValue ("{\"f\":{\"@class\":\"foo.Test$Bar\"}}",
m.constructType (Test.class.getDeclaredField
("foo").getGenericType
()));
System.out.println ("3) " + o);
System.out.println ("4) " + m.writeValueAsString (o));
System.out.println ("5) " + m.readValue (m.writeValueAsString (o),
m.constructType
(Test.class.getDeclaredField
("foo").getGenericType ())));
}
}
The last sysout does not work unless you comment in the @JsonGetter (the
hack to make it work) but then the type information appears twice if you
just serialize the object itself - not as being part of a collection
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