Assets

Asset routes in Krop provide special support for serving assets. Assets are files, such as CSS stylesheets, that are part of your web application and not written in Scala. An asset route does two things:

1. It monitors a directory of files, calculating a hash of each file in the directory and updating that hash whenever it changes.

2. It constructs names for asset files that include the hash of the file. The means each version of the file is served with a unique file name, preventing web browsers from caching and using out-dated versions of assets.

Using Assets

If you aren't using the project template you will need to add the following dependency to your build.sbt:

libraryDependencies += "org.creativescala" %% "krop-asset" % "0.10.0"

Creating an Asset Route

An AssetRoute is constructed by giving it a Path under which to serve assets, and a String specifying a directory to monitor. So, for example, if we want to serve assets under the path /assets, and those assets live under the directory resources/myapp/assets (relative the project root directory) we would create an AssetRoute as

import krop.all.*
import krop.asset.AssetRoute

val assets = AssetRoute(Path / "assets", "resources/myapp/assets")

Note we need to import krop.asset.AssetRoute; this not part of the core library we import with krop.all.*.

An asset route is also a handler, which we add to our application in the usual way. Code like the following will do.

assets.orElse(theApplication)

Linking to an Asset

Call the asset method on an asset route when you want to link to an asset, for example in a template. Pass the method the path to the asset, relative to the directory you passed the asset route on construction.

For example, if we have a file resources/myapp/assets/css/myapp.css we would call

assets.asset("css/myapp.css")
// res: String = /assets/css/myapp-1234.css

Notice the result includes the Path we created the asset route with. It also includes the value of a hash of the file (in the example replaced with 1234 for simplicity.) This value changes every time the file changes, and thus prevents the browser from using a stale cached copy.

The asset method requires a given KropRuntime value, which is available to all handlers when they handle a request.