Jackson ObjectMapper: How to omit (ignore) null array element [null]

Question

I have Json array containing null value in array.

{
  myArray: [ null ]
}

How to configure Jackson ObjectMapper to ignore such null array elements - as if it was empty array []?

Constrains:

No control of source class - it is a third party class
Array element type is unknown upfront
Array(s) name is unknown upfront

I don’t believe Jackson has this out of the box. You’ll need a custom deserializer. Or strip it yourself from the pojo. — Sotirios Delimanolis, Mar 17 '21 at 15:06
@SotiriosDelimanolis Do you know a way how to plugin some post-processor to ObjectMapper? — Michal Foksa, Mar 17 '21 at 15:07
No, I think it’ll be quite involved process. Find the standard list/set/collection and array deserializers, wrap them in the processor(s), then reregister them to deserialize those types. Might be easier to change your server ‍♂️ — Sotirios Delimanolis, Mar 17 '21 at 15:17

score 2 · Answer 1 · answered Mar 17 '21 at 21:51

2

You can use contentNulls property from JsonSetter annotation. Your POJO class could look like below:

class ArrayWrapper {
    private List<String> myArray;

    @JsonSetter(contentNulls = Nulls.SKIP)
    public void setMyArray(List<String> myArray) {
        this.myArray = myArray;
    }

    public List<String> getMyArray() {
        return myArray;
    }
}

See also:

How to exclude null list items with Jackson

answered Mar 17 '21 at 21:51

Michał Ziober

37,175
18
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It seems to go in correct direction, but I cannot modify POJOs (or very hardly). I am looking for a solution with configuration ObjectMapper itself only. – Michal Foksa Mar 18 '21 at 06:31
@MichalFoksa, use `MixIn` feature. Examples: [Dynamic addition of fasterxml Annotation?](https://stackoverflow.com/a/25306786/51591), [Jackson conditional @JsonUnwrapped](https://stackoverflow.com/a/25435990/51591) – Michał Ziober Mar 18 '21 at 08:19
:( Mixin is not generic - it does not apply for every array / list. – Michal Foksa Mar 18 '21 at 08:41
@MichalFoksa, could you edit your question and add more details? Could you create an example where `MixIn` does not apply to array/list? – Michał Ziober Mar 18 '21 at 09:08

score -1 · Answer 2 · answered Mar 17 '21 at 15:13

-1

Maybe @JsonIclude works?

   @JsonInclude(value=Include.NON_EMPTY, content=Include.NON_NULL)

http://fasterxml.github.io/jackson-annotations/javadoc/2.9/com/fasterxml/jackson/annotation/JsonInclude.html?is-external=true

answered Mar 17 '21 at 15:13

PhilBa

732
4
16

2

I believe this applies to the field, not to the contents of the JSON array. Have you tried it? – Sotirios Delimanolis Mar 17 '21 at 15:15

Jackson ObjectMapper: How to omit (ignore) null array element [null]

2 Answers2