So, what happens is that while you think you are giving a
List<ExampleContent> (or List<AbstractContent>), what runtimes sees is a
List<? extends Object>. Since `Object` has no `@JsonTypeInfo`, no type is
included.
You have been tripped by Java Type Erasure. Also, my general suggestion is
to NEVER EVER use generic type as the root type, but always use a
non-generic type. There are multiple ways to do that. Like:
1. Always use a POJO to contain Lists, Maps (wrapper)
2. Sub-class Lists, Maps:
public class ExampleList extends ArrayList<AbstractContent> { }
because this does retain type information
But there is also one way to make generic root type to work (although with
caveats)
1. Use `ObjectWriter`, specifying actual type, without erasure:
mapper.writerFor(new TypeReference<List<AbstractContent>>() {
}).writeValueAsString(list);
in this case you may hit other problems, since type is now fixed for
content as well, so this may fail for some type definitions.
-+Tatu +-
On Thu, Oct 6, 2016 at 5:53 PM, krrrr38 <[email protected]> wrote:
> Hi. I use jackson-databind 2.8.3.
>
> I want to serialize value with `@JsonTypeName`. When serialize with
> `List`, the property value is not shown.
>
> public class Main {
> public static void main(String[] args) throws Exception {
> ObjectMapper om = new ObjectMapper();
> System.out.println(om.writeValueAsString(new ExampleContent()));
> System.out.println(om.writeValueAsString(Arrays.asList(new
> ExampleContent())));
> }
>
> @JsonTypeInfo(
> use = JsonTypeInfo.Id.NAME,
> include = JsonTypeInfo.As.PROPERTY,
> property = "type",
> visible = true
> )
> @JsonSubTypes({
> @JsonSubTypes.Type(ExampleContent.class)
> })
> abstract static public class AbstractContent {
> }
>
> @JsonTypeName("text")
> public static class ExampleContent extends AbstractContent {
> }
> }
>
>
> result
>
> {"type":"text"}
> [{}]
>
>
> expected?
>
> {"type":"text"}
> [{"type":"text"}]
>
> Do I need to add more annotation or something?
>
> Regargs.
>
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