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Custom JSON marshallers

Gradle setup

    compile group: "org.http4k", name: "http4k-core", version: "3.238.0"
    compile group: "org.http4k", name: "http4k-format-jackson", version: "3.238.0"

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: