Custom JSON marshallers
compile group: "org.http4k", name: "http4k-core", version: "3.241.0" compile group: "org.http4k", name: "http4k-format-jackson", version: "3.241.0"
Custom auto-mapping JSON configurations
http4k declares an extended set of "primitive" types which it can marshall out of the box - this includes the various http4k primitives (Uri, Status), as well as a bunch of common types from the JDK such as the DateTime classes and Exceptions. These primitives types cannot be marshalled as top-level JSON structures on their own so should be contained in a custom wrapper class before transmission.
You can declare your own custom marshaller by reimplementing the Json instance and adding mappings for your own types - either uni or bi-directional.
This ability to render custom types through different JSON marshallers allows API users to provide different "views" for different purposes - for example we may wish to hide the values of some fields in the output, as below: