Prevent coercion of int from empty String to null if DeserializationFeature .FAIL_ON_NULL_FOR_PRIMITIVES is true

[yzmyyff]

I got 0 from the code below.

int i = mapper.readValue("\"\"", int.class);
System.out.println(i);

It seems that Json Number type cannot start with ".
Could I make the code throw some Exceptions?

[cowtowncoder]

So you would not want empty String to be coerced into 'missing' value of '0'?

Perhaps a DeserializationFeature could be added to prevent this -- there may already exist an issue for this.

[yzmyyff]

I tried to add DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT to my mapper, but it still print 0.

ObjectMapper mapper = new ObjectMapper();
mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
mapper.enable(DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES);
int i = mapper.readValue("\"\"", int.class);
System.out.println(i);

The right order in my mind is empty Json String -> Json Null -> Json Number -> primitive.
it seems that these 2 features don't take effect at the same time.

[cowtowncoder]

@yzmyyff Correct, the features in question are handled separately. Or, I should say, coercion from empty String into scalars does NOT consider ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, as scalars are not (Java) Objects. It is confusing. I will think about this to see if adding checks as you suggest is the best way to go, or adding a new DeserializationFeature. I have some concerns about backwards compatibility, if changing existing behavior, but perhaps those are not valid.

[cowtowncoder]

I think this would make sense. I elaborated bit more on #1106.

[yzmyyff]

Thanks a lot.

[cowtowncoder]

Implemented for 2.7.1; affects primitives, but not equivalent wrappers, as per naming of features.

[gkozyryatskyy]

What should I do if i want this

Integer i = mapper.readValue("\"\"", Integer.class);
System.out.println(i);

to throw Exception?

[cowtowncoder]

Was about to say that it works, but then realized you are talking about wrapper object.

DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT is the thing to disable if you do not want such coercion. Handling has been rewritten for 2.9 (not yet released, but 2.9.0.pr2 is available) and this will work; earlier versions had more limited support for some types. I do not know offhand if Integer handling was working or not.

[gkozyryatskyy]

@cowtowncoder
Im using 2.8.6 and I try with 2.9.0.pr2
mapper.configure(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, false);
And there is no exception... Empty string is successfully parsed as null Integer or Long.

[cowtowncoder]

@gkozyryatskyy Ok I'll have a look; since this issue is closed, I'll file a new one.

[gkozyryatskyy]

@cowtowncoder
thx a lot!

[cowtowncoder]

Ok actually I misspoke here. Due to backwards compatibility requirements, DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT can not be made to apply to scalar values: feature defaults to false, yet behavior of coercion is enabled by default.

So: #1106 will actually be needed here; feature to be added is MapperFeature.ALLOW_COERCION_OF_SCALARS and will be included in 2.9,0.pr3.