This includes most common Java types, however additional instances can be registered simply be creating beans of type TypeConverter.

    @Get("/headerInferred")
    String headerInferred(@Header String contentType) {
        // ...
    }

    @Get("/headerInferred")
    fun headerInferred(@Header contentType: String): String {
        // ...
    }

In this case if the HTTP header Content-Type is not present in the request the route is considered invalid, since it cannot be satisfied and a HTTP 400 BAD REQUEST is returned.

    String headerNullable(@Nullable @Header String contentType) {
    }

    @Get("/headerNullable")
    fun headerNullable(@Header contentType: String?): String? {
        // ...
    }

An null string will be passed if the header is absent from the request.

    @Get("/date")
    String date(@Header ZonedDateTime date) {
        // ...
    String dateFormat(@Format("dd/MM/yyyy hh:mm:ss a z") @Header ZonedDateTime date) {
        // ...
    }

    @Get("/date")
    fun date(@Header date: ZonedDateTime): String {
        // ...
    }
    @Get("/dateFormat")
    fun dateFormat(@Format("dd/MM/yyyy hh:mm:ss a z") @Header date: ZonedDateTime): String {
    }