Hi experts.
I have a question about marshalling / unmarshalling java 8 Optionals.
Dmitry already made some suggestion about optionals, but lets elaborate
a bit on them. They are a bit of special case. Logically Optional fields
are not intended to be null, but technically it is possible. It makes
some impact on marshalling / unmarshalling considerations.
Basic question is: Should empty Optionals be skipped during
serialization or serialized as keys with null values? Should optional
properties honor @JsonbNillable configuration?
Given a class:
@JsonbNillable(true|false)
class Pojo {
Optional<Component> pojoComponent;
String strField;
}
1. Consider empty Optionals are serialized as missed in a JSON document
and we also honor @JsonbNillable setting.
If @JsonbNillable is set to true all is nice and easy:
Pojo pojo = new Pojo();
pojo.pojoComponent = Optional.empty(); //this have actually no effect on
JSON document result
jsonb.toJson(pojo);
//Will produce {"pojoComponent":null,"strField":null} JSON.
During unmarshalling of such JSON document we will set pojoComponent to
Optional.empty()
If @JsonbNillable is not set or set to false we will result with JSON:
Pojo pojo = new Pojo();
jsonb.toJson(pojo);
//Will produce "{}" JSON.
pojo.pojoComponent = Optional.empty();//no effect
jsonb.toJson(pojo);
//Will produce "{}" JSON again.
Now when we will unmarshall such JSON document with missing keys for
Optionals, we don't know if they were actually Optional empty or null.
Furthermore, our JSONB Unmarshaller is driven by JSONP parser events,
and I will get no event for any keys that are missing in document. So if
I would like to set all Optional fields with null value to
Optional.empty() (which makes most sense) it would have to be done by
some kind of postprocessing.
Things get even more complicated considering Arrays of Optionals. Array
of Optionals of size 3 with either: 3 null values or 3 empty Optionals
always have to be serialized as [null,null,null] in JSON document. It is
inconsistent according to serializing Optional properties.
Another option is not to honor @JsonbNillable setting and serialize null
properties of Optionals as missing in JSON document and Optional.empty()
values as JSON keys with null values. This will be consistent with
Optional Arrays and we will explicitly know when and where to set
Optional.emtpy() during unmarshalling, but it will be inconsistent with
marshalling non Optional object properties set to null with
@JsonbNillable set to false (default).
Do you have any considerations about this?
Thank you,
Roman