jackson-dataformat-xml: null-handling ignored

With 2.12.1-SNAPSHOT the following code:

        XML_MAPPER = new XmlMapper();
        XML_MAPPER.configOverride(List.class).setSetterInfo(JsonSetter.Value.forValueNulls(Nulls.AS_EMPTY));
        XML_MAPPER.configOverride(Set.class).setSetterInfo(JsonSetter.Value.forValueNulls(Nulls.AS_EMPTY));
        XML_MAPPER.configOverride(Map.class).setSetterInfo(JsonSetter.Value.forValueNulls(Nulls.AS_EMPTY));
        XML_MAPPER.enable(FromXmlParser.Feature.EMPTY_ELEMENT_AS_NULL);

        List<LoggerTO> original = new ArrayList<>();

        StringWriter writer = new StringWriter();
        XML_MAPPER.writeValue(writer, original);

        List<LoggerTO> actual = XML_MAPPER.readValue(writer.toString(), new TypeReference<List<LoggerTO>>() {
        });
        assertEquals(original, actual);

fails with message

org.opentest4j.AssertionFailedError: expected: <[]> but was: <null>

I have verified that serialization produces

<ArrayList/>

About this issue

Original URL
State: closed
Created 4 years ago
Comments: 22 (12 by maintainers)

Most upvoted comments

For what it is worth, empty element like <ArrayList></ArrayList> (or <ArrayList />) should be deserialized as empty List with 2.12, as long as you do NOT enable FromXmlParser.Feature.EMPTY_ELEMENT_AS_NULL. This was not the case with 2.11, regardless of setting as handling of empty elements had problems – mostly because at low level such elements would be equivalent to JSON empty String value. Support for this case was improved in jackson-databind 2.12, to let XML module work better for this relatively common case.

I hope it is now possible to get things to work in a usable way: unfortunately the full combination of various aspects is not easy to reason about and it can be frustrating to find a good combination. Especially when attempting to make things work the same way against different versions.

I am planning to release 2.12.1 very soon now, for what that is worth; there are a few important fixes.

cowtowncoder on Jan 1, 2021