Getter that returns an abstract collection breaks a delegating `@JsonCreator`

Using version 2.9.2 or 2.9.8 (and probably many other versions), the following test throws:

JsonMappingException: Cannot find a deserializer for non-concrete Collection type [collection type; class java.util.AbstractSet, contains [simple type, class java.lang.Integer]]

    @Test
    public void testDeserializeValSet() throws IOException {
        new ObjectMapper().readValue("[1,2,3]", ValSet.class);
    }

    static class ValSet {
        @JsonValue
        private final AbstractSet<Integer> vals;

        @JsonCreator(mode = Mode.DELEGATING)
        ValSet(Collection<Integer> vals) {
            this.vals = new HashSet<>(vals);
        }

        public AbstractSet<Integer> getVals() {
            return vals;
        }
    }

This is a spurious error since the @JsonCreator constructor only requires Collection<Integer>, not AbstractSet<Integer>.

Some workarounds:

• Delete getVals().
• Make getVals() non-public.
• Move @JsonValue to getVals().
• Add @JsonIgnore to getVals().
• Add @JsonAutoDetect(getterVisibility = Visibility.NONE) to ValSet.

[cowtowncoder]

@2is10 Ok. Yes, I hope to solve that one still.

And just in case it might help, there is the SimpleModule.addAbstractTypeMapping() that allows specifying a mapping – the reason it could potentially help (if you can think of a concrete subtype) is that although it is not necessary for deserializer to actually work, existence is required: so you could map abstract type to any other subtype for which a valid deserializer could be created (regardless of whether it would actually work if ever called).

Or, I guess you could also register bogus custom deserializer, which similarly should never actually get called.

Still, I hope I can fix #2252 itself in future.

[2is10]

Thanks @cowtowncoder!

Note: In my actual code, the abstract Set class that triggered the problem was Guava’s ImmutableSet, so I’m personally still invested in a solution to #2252. (I didn’t want to introduce a dependency on jackson-datatypes-collections/guava as a workaround.)