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Static Assets

Example application

Http4k provides out of the box a set of components for serving static assets and Invirt only adds a few utilities to make caching and versioning easier.

val staticAssetsVersion = gitCommitId()!!
val devMode = Environment.ENV.developmentMode

val config = InvirtConfig(
    developmentMode = devMode,
    pebble = InvirtPebbleConfig(
        globalVariables = mapOf("staticAssetsVersion" to staticAssetsVersion)
    )
)
val appHandler = Invirt(config).then(
    routes(
        "/" GET { renderTemplate("index") },
        "/static/${staticAssetsVersion}" bind cacheDays(365).then(staticAssets(devMode))
    )
)

Assets version​

The first key element here is staticAssetsVersion which is passed as a global variable in the InvirtPebbleConfig setup. As a Pebble variable, this value can then be used directly in a Pebble template to include assets dynamically, as per example below.

<script src="/static/{{ staticAssetsVersion }}/app.js"></script>

In the above example we use the Git commit id to version static assets, which is achieved by a call to Invirt's gitCommitId(). This function is discussed in detail here.

Caching​

The function cacheDays(days) is a simple wrapper over http4k's built-in caching filter and only exists as a convenience over the construct below.

CachingFilters.CacheResponse.MaxAge(Duration.ofDays(days.toLong()))

Hot reload vs classpath loading​

All the function staticAssets() does is to wrap http4k's static assets wiring, and allows easily switching between hot reload and caching classpath loading of these assets, similarly to how views are loaded.

fun staticAssets(
    developmentMode: Boolean,
    classpathLocation: String = "webapp/static",
    directory: String = "src/main/resources/webapp/static"
): RoutingHttpHandler = if (developmentMode) {
    static(ResourceLoader.Directory(directory))
} else {
    static(ResourceLoader.Classpath(classpathLocation))
}