Add support for @JsonMerge to allow "deep update"

[cowtowncoder]

Currently existing values of properties are not taken into consideration, with the rare case of "setterless-getters" where this is done for Collection types if no setter exists.
But it would be useful to allow this for Maps and POJOs as well.

Proposed mechanism is to allow use of:

public class POJO {
    @JsonSetter(merge=OptBoolean.TRUE)
    public List<String> names = new ArrayList<>();
    {
         names.add("first");
    }

In addition to per-property annotation, it should also be possible to specify "config overrides" using:

objectMapper.configOverrides(MyPOJO.class)
     .setter(JsonSetter.Value.from(.....));

which would specify default merge/no-merge settings for properties of specified type.
It would probably also make sense to allow setting fully global default, similar to ability to set "serializationInclusion" global defaults (with JsonInclude.Value).

[cowtowncoder]

Initial implementation now exists, supporting POJOs, Collections, Maps, reference types.

[heruan]

Any docs on how to test this?

[cowtowncoder]

@heruan at this point the best way I think is to search for unit tests with @JsonSetter(merge=.

[Tetradeus]

Wouldn't it be nice to have an option to enable setting null values at merge path ? Ref #1437

    // Also: nulls better not override
    public void testBeanMergingWithNull() throws Exception
    {
        Config config = MAPPER.readerForUpdating(new Config(5, 7))
                .readValue(aposToQuotes("{'loc':null}"));
        assertNotNull(config.loc);
        assertEquals(5, config.loc.a);
        assertEquals(7, config.loc.b);
    }

What if I really want to be able to set null for loc ? assertNull(config.loc);

Thanks for your reply.

[cowtowncoder]

@Tetradeus Please file a new issue; this one is closed. We can discuss details as part of that.