gistfile1.java

/*

Soooo, I have a POJO with an Optional<T> field that *isn't set by default*. When the field isn't included in
a JSON document, I'd like that field to be deserialized as Optional.absent() rather than 'null'. Just doing
the default thing (below) I end up having the Optional<T> field being set to null after deserialization.

I suspect that Jackson is being smart and just not setting fields that aren't in the JSON. Is there something
I can do to make sure it initalizes all the fields, or is the Right Thing To Do just to give my Optional<T>
field a default value?

*/
public class AbsentTest {
    public static class Nothing {
        public Nothing() {/*jackson*/}

        private Optional<Set<String>> optionalSet;

        public Optional<Set<String>> getOptionalSet() {
            return optionalSet;
        }

        @Override
        public String toString() {
            return "Nothing{" +
                    "optionalSet=" + optionalSet +
                    '}';
        }
    }

    /**
     * Outputs "Nothing{optionalSet=null}"
     */
    @Test
    public void testWithNoValues() throws IOException {
        final ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(new GuavaModule());

        System.err.println(mapper.readValue("{}", Nothing.class));
    }

    /**
     * Outputs "Nothing{optionalSet=Optional.of([3, 2, 1])}"
     */
    @Test
    public void testWithSomeValues() throws IOException {
        final ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(new GuavaModule());

        System.err.println(mapper.readValue("{\"optionalSet\": [\"1\", \"2\", \"3\"]}", Nothing.class));
    }
}