Customise a Server backend

How to write a custom server implmentation

Whilst the http4k server modules ship with a sensibly configured standard server-backend setup, a lot of projects will require specialised implementations of the underlying server backend. http4k makes this easy with the ServerConfig interface.

Gradle setup

dependencies {

The example below shows a customised Jetty setup which enables HTTPS traffic by reimplementing the ServerConfig interface. The idea is that this single class will encapsulate the usage of the Server platform API behind the http4k abstraction and provide a simple way to reuse it across different applications.


package guide.howto.customise_a_server_backend

import org.eclipse.jetty.server.HttpConfiguration
import org.eclipse.jetty.server.HttpConnectionFactory
import org.eclipse.jetty.server.SecureRequestCustomizer
import org.eclipse.jetty.server.Server
import org.eclipse.jetty.server.ServerConnector
import org.eclipse.jetty.server.SslConnectionFactory
import org.eclipse.jetty.util.ssl.SslContextFactory
import org.http4k.core.HttpHandler
import org.http4k.core.Response
import org.http4k.core.Status
import org.http4k.core.then
import org.http4k.filter.DebuggingFilters.PrintRequestAndResponse
import org.http4k.server.Http4kServer
import org.http4k.server.ServerConfig
import org.http4k.server.asServer
import org.http4k.server.toJettyHandler

class SecureJetty(
    private val sslPort: Int,
    private val localKeyStorePath: String,
    private val localKeystorePassword: String,
    private val localKeyManagerPassword: String

) : ServerConfig {
    override fun toServer(http: HttpHandler): Http4kServer {
        val server = Server().apply {
            val https = HttpConfiguration().apply {

            val sslContextFactory = SslContextFactory.Server().apply {
                keyStorePath = localKeyStorePath
                keyStorePassword = localKeystorePassword
                keyManagerPassword = localKeyManagerPassword

            connectors = arrayOf(
                    SslConnectionFactory(sslContextFactory, "http/1.1"),
                ).apply { port = sslPort }


        return object : Http4kServer {
            override fun start(): Http4kServer = apply { server.start() }

            override fun stop(): Http4kServer = apply { server.stop() }

            override fun port(): Int = if (sslPort > 0) sslPort else server.uri.port

fun main() {
    PrintRequestAndResponse().then { Response(Status.OK).body("hello from secure jetty!") }
                sslPort = 9000,
                localKeyStorePath = "keystore.jks",
                localKeystorePassword = "password",
                localKeyManagerPassword = "password"