Provide a way to use an alternate JSON mapper

[MT-Jacobs]

Feature description

Using the default Micronaut ObjectMapper is good and all when setting up Elasticsearch clients:

https://github.com/micronaut-projects/micronaut-elasticsearch/blob/48e0b0c/elasticsearch/src/main/java/io/micronaut/elasticsearch/DefaultElasticsearchClientFactory.java#L83-L88

but let's say our service is using multiple features that rely on using a shared ObjectMapper, like the HTTP server and elasticsearch-java.

If you provide any serialization specialization for Elasticsearch, it impacts the HTTP server, and vice-versa.

As one example, the default ObjectMapper that Micronaut provides doesn't serialize dates correctly; passing an Instant within a class results in the fields being serialized to an array, which to ES looks like we're passing multiple dates of very low values (2022 in the Unix Epoch is 2,022 seconds after Jan 1 1970). The workaround is to apply a @JsonFormat override to every Instant:

@JsonFormat(shape = JsonFormat.Shape.STRING)

If we attempt to use write-dates-as-timestamps as documented here:

micronaut-projects/micronaut-core#240 (comment)

this will fix elasticsearch-java's serialization behavior, but it will also change the http-server serialization behavior.

One solution would be to provide an alternate ObjectMapper from the default one for micronaut-elasticsearch. Is this a workable idea?

[graemerocher]

yeah that is certainly an idea, wonder if we need to add support in Micronaut Serialization for configuring alternative mappers

[MT-Jacobs]

Not sure how I missed this before, but I bet we could use @JacksonFeatures to facilitate this the same way that declarative HTTP clients do:

https://docs.micronaut.io/3.7.4/guide/#clientJackson

Will definitely require a code change here though.