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SBT Resource Management

SBT Resource Management is a plugin designed to handle:

  • Compiling CoffeeScript to JavaScript.
  • Compiling SASS to CSS via compass.
  • Combining and compressing JavaScript files via YUI Compressor.
  • Combining and compressing CSS stylesheets via YUI Compressor.
  • Deploying combined/compressed JS and CSS to Amazon S3.

Commands are provided for each of these steps, and some convention-based configuration is used to bundle JS and CSS into bundles that can be used in Lift. Notably, there is a component of the bundling process that requires support in the Lift app, not in sbt. More on that in a moment.

Adding as a plugin

To add sbt-resource-management to your project, add the following to your project/plugins.sbt file:

addSbtPlugin("com.openstudy" % "sbt-resource-management" % "0.5.0")


To get started you have to import the settings from this plugin:

seq(resourceManagementSettings :_*)

If you're interested in deploying your assets to S3, you need to specify the access key, the secret key, and the name of the bucket in your build.sbt file. After your import of the default resource management settings, add the following lines to set up S3 deployment.

awsAccessKey := Some("YOUR_ACCESS_KEY")

awsSecretKey := Some("YOUR_SECRET_KEY")

awsS3Bucket  := Some("YOUR_S3_BUCKET")

If you are using IAM roles to authorize your deployment machine to deploy to the S3 bucket, you can leave off the access key and secret key.


By default, the following directories/files are used; listed beside them are the variables that can be used to customize these:

  • src/main/webapp/*/javascripts for JavaScript (scriptDirectories in ResourceCompile)
  • src/main/webapp/*/stylesheets for CSS (styleDirectories in ResourceCompile)
  • src/main/webapp/**/*.coffee for CoffeeScript (coffeeScriptSources in ResourceCompile)
  • target/compiled-coffee-script for compiled CoffeeScript (compiledCoffeeScriptDirectory in ResourceCompile)
  • target/javascripts for all JavaScript + compiled CoffeeScript (targetJavaScriptDirectory in ResourceCompile)
  • target/compressed for compressed JS and CSS (compressedTarget in ResourceCompile) (javascripts and stylesheets directories are created under this one for each type of file).

SASS/Compass specifics

By default, Compass runs a normal compass compile. If you wish to force compilation every time, add the following line to your settings:

forceSassCompile := true


The main command for JavaScript is sbt resources:copy-scripts. This does two things:

  • Compile any CoffeeScript (resources:compile-coffee-script) to the compiled CoffeeScript directory.
  • Copy any regular JavaScript files and any compiled CoffeeScript files to the target JavaScript directory, from where they can be served jointly.

For SASS files, you can run sbt resources:compile-sass. Notably, this runs the compass command, so compass must be installed and you must have a config.rb file in your project root. It also sets the asset_domain environment variable to the value of awsS3Bucket, which is used by compass to create proper asset paths, and sets the compass environment to production. You can use this in your config.rb to act differently in the face of production settings (we use this to enable relative_assets only when the environment is NOT production and to toggle the output style from between compressed and expanded).

If the awsS3Bucket setting is not set, then the asset_domain environment variable is not set either.

Bundles and compression

SBT resource management offers a relatively simple way to bundle JavaScript files together, use them normally in development, and then combine them in production. By default, it looks in the src/main/resources/bundles directory (bundleDirectory in ResourceCompile) for two files: javascript.bundle (scriptBundle in ResourceCompile) and stylesheet.bundle (styleBundle in ResourceCompile).

These files take the following form:



The bundle names have no extension, while the files inside them are expected to have their proper file extension. For example, we have this in OpenStudy's javascript.bundle:


The resulting bundle will be called landing.js in production, and will contain the contents of the files listed below it.

CSS is similar:


The resulting bundle here is landing.css.

You can also reference another bundle name in a bundle to include its files in the current bundle. For example:


The above super-landing.js bundle would include everything in the landing bundle, plus the more-landing.js and massive-landing.js files.

In the event that you need to deploy some bundles to buckets other than the one specified in the awsS3Bucket setting, the bundle file format supports that as well. Simply add an arrow after the end of the bundle name and provide the name of the bucket you wish to have that bundle deployed to. To define a bundle that should go to, you would write something like this:


Scripts and CSS are combined and compressed with the two commands:

$ sbt resources:compress-scripts
$ sbt resources:compress-styles

These read the above bundle definitions and create the appropriate combined, compressed bundle files, dropping them in the compressed target directory from above. Note that compress-scripts first runs copy-scripts, and so will compile CoffeeScript if needed.

There is a combination command, resources:compress-resources, that runs both the compression commands.

When sbt-resource-management compresses your resources, it also drops 2 files in the resources directory alongside the javascript.bundle and stylesheet.bundle files. These files describe the "versions" of the resulting bundles. By default, they are in the bundles directory at javascript-bundle-versions (scriptBundleVersions in ResourceCompile) and stylesheet-bundle-versions (styleBundleVersions in ResourceCompile). An example of a javascript-bundle-versions file from OpenStudy:


The versions here are MD5 hashes, and can be used to append a cache-buster querystring to your script and link tags. Also note the checksum-in-filename entry at the top, which is explained below.

You can also "mash" the scripts, meaning create the joined bundle files without YUI compression, by running sbt resources:mash-scripts.

Deployment to S3

If you defined the AWS settings above, SBT resource management can also push your compressed script and CSS bundles to S3. Just run:

$ sbt resources:deploy-scripts
$ sbt resources:deploy-styles

This will create javascripts/ and stylesheets/ directories in the specified S3 bucket with the specified bundles.

Once again, there is a combination command, resources:deploy-resources, that runs both the deploy commands.


By default, resources are stored in S3 in their original forms; however, you can request that they be gzipped and stored in S3 with a gzipped content encoding, so that they are served to the browser gzipped and the browser decompresses them automatically. To do this, simply enable the flag gzipResources:

gzipResources := true

Checksums as part of the filename

As noted by @eltimn and recommended by Google, "Most proxies, most notably Squid up through version 3.0, do not cache resources with a "?" in their URL even if a Cache-control: public header is present in the response." sbt-resource-management supports including the checksum as part of the filename by setting the checksumInFilename in ResourceCompile setting to true. It is false by default.

As seen above, the bundle-version files left by sbt-resource-management include a line indicating whether the bundles were generated with their checksums included in the filenames or not. This information can then be used to construct the appropriate filename.

Bundles: the Lift side

The Lift side of bundles is provided by a simple singleton object, called Bundles and set up at Boot as two snippets: script-bundle and style-bundle. The source for the relevant snippets is at . Somewhere in your Boot process, you can add:


This will install the snippets. You can then refer to any of the bundles in your bundle files by name:

  <lift:style-bundle name="feed" />

  <lift:script-bundle name="feed" />
  <lift:script-bundle name="tools" />
  <lift:script-bundle name="group" />
  <lift:script-bundle name="loading" />

Notably, the bundle snippets above will include the expanded, unbundled files in development mode, and only try to include the bundled files in production mode. When the bundled files are included, the version files from the above bundling step are used to append the proper version to the script and link tags, either as a querystring parameter or as part of the filename, depending on the checksum-in-filename setting. When the non-bundled files are included, Lift's internal attachResourceId is used to attach the cache-busting querystring. attacheResourceId by default attaches a different unique id every time the server is run, but uses the same one within the same server run. You can change that by replacing LiftRules.attachResourceId.


sbt-resource-management is provided under the terms of the MIT License. See the LICENSE file in this same directory.


sbt-resource-management is copyright me, Antonio Salazar Cardozo, and licensed uner the terms of the MIT License. No warranties are made, express or implied. See the LICENSE file in this same directory for more details.

I have a rather sporadically updated blog at

I am the Director of Engineering at OpenStudy, where we're working on changing the face of education as we know it using Scala, Lift, and a variety of other cool tools.

Also contains contributions from Matt Farmer, @farmdawgnation and Mike Rivera, @riveramj, two of the stupidly smart developers at Elemica.


Provides tasks to compile coffee script and compass/SASS files, plus tasks to bundle and upload to S3.







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