Cannot read Optionals written with StdTypeResolverBuilder

[isopov]

The following test fails on Jackson 2.9.7 and passes on 2.8.11:

    @Test
    public void test() throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        mapper.setDefaultTyping(
                new StdTypeResolverBuilder()
                        .init(JsonTypeInfo.Id.CLASS, null)
                        .inclusion(JsonTypeInfo.As.WRAPPER_OBJECT)
        );
        mapper.registerModule(new Jdk8Module());
        String json = mapper.writeValueAsString(new Foo(Optional.of(1)));
        System.out.println(json);
        mapper.readValue(json, Foo.class);
    }

    public static class Foo {
        private Optional<Integer> bar;

        public Foo() {
        }

        public Foo(Optional<Integer> bar) {
            this.bar = bar;
        }

        public Optional<Integer> getBar() {
            return bar;
        }

        public void setBar(Optional<Integer> bar) {
            this.bar = bar;
        }
    }

Complete runnable project with this test-case can be found on https://github.com/isopov/jackson-optional-test

[isopov]

Added workaround, involving copy&pasting classes from 2.8.11 - https://github.com/isopov/jackson-optional-test/blob/workaround/src/test/java/com/example/OptionalJacksonTest.java

Still proper fix will be highly appreciated.

[cowtowncoder]

I will have to say that it is quite possible that combination of polymorphic type in Optional for root value may be unsupportable. I would strongly recommend not using that combination: partly since root values have significant challenges wrt type erasure, and partly as Optionals are challenging in their own right.

In fact I am considering adding a warning that polymorphic type handling is not recommended to be used for root values at all.

Having said that: I will try to figure out if this can be made to work correctly (although depending on changes they might only be made to 2.9 branch), and I hope this is the case.

Thank you for reporting the problem.

EDIT Looking at this further, Optional is NOT used as root value. So that's not the problem.

[cowtowncoder]

To help future work, output looks like:

{"com.fasterxml.jackson.datatype.jdk8.PolymorphicOptionalTest$Foo":{"bar":1}}

and that would seem to be missing type information for contents, somehow.