How to skip Optional.empty fields during Jackson serialization?

Question

I have a Java class with an Optional field. I am serializing the class to JSON using Jackson 2.8.3 (called from Spring web 4.3.3).

I am hoping to get the serializer to skip the field if the Optional is empty, and serialize the contained string if it is present. An example of the result I'm looking for with a list of two objects:

[
    {
        "id": 1,
        "foo": "bar"
    },
    {
        "id": 2,
    }
]

Here the foo Optional is empty for the object with id 2.

Instead, what I get is:

[
    {
        "id": 1,
        "foo": {
            "present": true
        }
    },
    {
        "id": 2,
        "foo": {
            "present": false
        }
    }
]

This is the result even if I annotate the "bar" field in the class like

@JsonInclude(JsonInclude.Include.NON_ABSENT)
public Optional<String> getFoo() { ...

Is there any way I can achieve a result like the first list using the Jackson annotations or a custom serializer?

As an aside, using Optional as a field of a bean is a Bad Idea™ in general. — biziclop
– biziclop, Commented Nov 3, 2016 at 19:05
It wasn't designed for that kind of use. It's a very subtle semantic difference but in the case of a field, null is considered just another value. While if you're designing a method in the API of a library, you might want to emphasise that it may not return a value, and thus use Optional. See more here — biziclop
– biziclop, Commented Nov 3, 2016 at 20:55

Vic Seedoubleyew · Accepted Answer · 2019-04-09 16:00:00Z

34

No need to write custom serializer. Annotate your class with @JsonInclude(JsonInclude.Include.NON_ABSENT).

You also need to:

include com.fasterxml.jackson.datatype:jackson-datatype-jdk8 as your dependency
and to register the corresponding module with your object mapper: objectMapper.registerModule(new Jdk8Module());

edited Apr 9, 2019 at 16:00

Vic Seedoubleyew

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answered Nov 3, 2016 at 17:57

Bartosz Bilicki

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3 Comments

André Risnes Over a year ago

Thanks, including the dependency on com.fasterxml.jackson.datatype:jackson-datatype-jdk8 did the trick.

GKVM Over a year ago

@JsonInclude(JsonInclude.Include.NON_ABSENT) will be good enough.

Robert Over a year ago

To exclude Optional.empty() fields, as the OP originally asked, one MUST add the depencandy and MUST set NON_ABSENT. NON_NULL is not enough.

Greenonline · Accepted Answer · 2020-08-01 21:45:16Z

4

You can use objectMapper.registerModule(new Jdk8Module()); but it serializes with null values.

But still you want to remove null values also from JSON, please use the following code:

objectMapper.registerModule(new Jdk8Module().configureAbsentsAsNulls(true));
objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);

edited Aug 1, 2020 at 21:45

Greenonline

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answered Aug 1, 2020 at 16:08

vikrant kumar

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Comments

Bartosz Bilicki · Accepted Answer · 2016-11-03 18:51:18Z

1

Use a JsonSerializer to your needs.

Something like this (semi-pseudo):

public class MySer extends JsonSerializer<Opional<?>> {

        @Override
        public void serialize(Optional<?> optString, JsonGenerator generator, SerializerProvider provider)
                                          throws IOException, JsonProcessingException {
        //Check Optional here...        
        generator.writeString(/* DO SOMETHING HERE WHATEVER */);
    }

//Then in your model:

public class ClassWhatever {           
    @JsonSerialize(using = MySer .class)
    public Optional<String> getFoo() { ...
 }

To avoid annotating every field with @JsonSerialize you may register your custom serializer to object mapper using

  ObjectMapper mapper = new ObjectMapper();
SimpleModule testModule = new SimpleModule("MyModule", new Version(1, 0, 0, null));
testModule.addSerializer(new MyCustomSerializer()); // assuming serializer declares correct class to bind to
mapper.registerModule(testModule);

Also, given solution works only for serialization. Deserialization will fail unless you write your own deserializer. Then you need to annotate every field with @JsonDeserialize or register your custom deserializer.

edited Nov 3, 2016 at 18:51

Bartosz Bilicki

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answered Nov 3, 2016 at 17:56

Mechkov

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2 Comments

Bartosz Bilicki Over a year ago

com.fasterxml.jackson.datatype:jackson-datatype-jdk8 is better option. with such custom solution you need to annotate every field. Also, deserialization will not work unless -you write custom deserializer and annotate every field with @JsonDeserialize

Mechkov Over a year ago

@BartoszBilicki Certainly, in agreement with you there. Both would work, but your recommendation is better.

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