A collection of Kotlin examples using the Hotwire JS framework to build interactive web apps with a Kotlin Armeria server backend.
Using Hotwire and kotlinx.html together has made building web apps fun again since I can build everything I want in sweet, sweet Kotlin.
Notably, the lack of WebSocket support in Armeria limits it being a complete backend for Hotwire JS. For example, Turbo Streams which require WebSockets do not currently work. Turbo Links and Turbo Frames work well. WebSocket support is being tracked here and hopefully will be added soon.
With the HTML to kotlinx.html IntelliJ Plugin, I could copy pasta any HTML UI code I found into a Kotlin file, and the corresponding kotlinx.html DSL would be generated and just work.
The one caveat is that for certain custom tags or attributes or somecases like ButtonType where kotlinx.html uses an enum you'll need to manually fix the DSL. Any required fixes were always straight forward in my testing.
The overall workflow of copying HTML from UI frameworks like Tailwind CSS, refactoring into Turbo Frame components, and adding props data classes for component inputs, proved to have the best of the React workflows I was used to without all the bad complex abstractions of React, Redux, Webpack, CSS-in-JS, and other novelties of the modern JS front end stack.
import xyz.adrw.hotwire.html.hotwire.turbo_frame
import xyz.adrw.hotwire.html.infra.template
import kotlinx.html.*
data class TableProps(
val data: List<List<String>>,
val limit: Int? = null,
val query: String? = null,
)
val TableId = "table_frame"
val Table = template<TableProps> { props ->
val header = props.data.first()
val dataRows = props.query?.let { query ->
props.data.drop(1).filter { row ->
row.any { it.contains(query) }
}
} ?: props.data.drop(1)
val truncated = dataRows.take(props.limit ?: 5)
turbo_frame(TableId) {
div("flex flex-col") {
div("-my-2 overflow-x-auto sm:-mx-6 lg:-mx-8") {
div("py-2 align-middle inline-block min-w-full sm:px-6 lg:px-8") {
div("shadow overflow-hidden border-b border-gray-200 sm:rounded-lg") {
table("min-w-full divide-y divide-gray-200") {
thead("bg-gray-50") {
tr {
header.map {
th(classes = "px-6 py-3 text-left text-xs font-medium text-gray-500 uppercase tracking-wider") {
attributes["scope"] = "col"
+it
}
}
...
The request lifecycle of encoding inputs within the request path and using a when statement to choose which component to return with new props was simple and straightforward, a joy to write and use.
/**
* Endpoint that handles interactive UI from Hotwire Turbo Frame related clicks
* Configuration of which UI to return and input data (ie. from forms) is provided by query parameters
*/
class TurboServiceHtml {
private val logger = getLogger<TurboServiceHtml>()
@Get
@Produces("text/html")
fun get(params: QueryParams): String {
val screen = params[ScreenParam]
val currentValue = params[BooleanParam].toBoolean()
val searchQuery = params[SearchParam]
val limit = params[LimitParam]?.toIntOrNull()
return buildHtml {
Wrapper("") {
when (screen) {
NavbarMobileMenuId -> NavbarMobileMenu(NavbarMobileMenuProps(visible = !currentValue))
NavbarAvatarMenuId -> NavbarAvatarMenu(NavbarAvatarMenuProps(visible = !currentValue))
TableId -> Table(TableProps(carsData, limit, searchQuery))
TableWithQueryId -> TableWithQuery(TableWithQueryProps(carsData, limit, searchQuery))
else -> logger.error("GET [screen=$screen] not found")
}
}
}
}
}Before building the project, you need to activate the Hermit environment, unless you are using the Hermit Shell Hooks or Hermit IntelliJ Plugin.
. ./bin/activate-hermit