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Typesafe RequestContexts

A RequestContext makes it possible to attach objects to a request whilst it is being passed down through the layers of an application.

The basic concept is that there is a global shared object which holds a bag of state (indexed by Request). This state can be modified in Filters and then that state accessed inside other Filters or the terminating HttpHandler. There are 2 available choices for manipulating this data:

  1. Using simple Strings to represent the keys.
  2. Using RequestContextKeys and the Lens mechanism from the http4k-core module.

Whilst the first method looks technically simpler, the use of simple Strings does not provide the type-safety of the second, which uses unique shared Key objects to guarantee non-clashing of keys and type-safety of the state. Regardless of which of the above mechanisms are used, an instance of the ServerFilters.InitialiseRequestContext Filter must wrap the HttpHandler(s) to activate the shared bag of state for each request, and to remove the state after the request is complete.

Gradle setup

    compile group: "org.http4k", name: "http4k-core", version: "3.241.0"

String-based keys

Lens-based keys