Compile sass to css on-the-fly via a j2ee servlet filter

Add the dependency to pom.xml

<dependency>
    <groupId>com.darrinholst</groupId>
    <artifactId>sass-java</artifactId>
    <version>3.4.4</version>
</dependency>

Add the filter to web.xml

<filter>
    <filter-name>SassCompiler</filter-name>
    <filter-class>com.darrinholst.sass_java.SassCompilingFilter</filter-class>
</filter>

<filter-mapping>
    <filter-name>SassCompiler</filter-name>
    <url-pattern>*.css</url-pattern>
</filter-mapping>

Create a WEB-INF/sass/config.rb

css_dir = "../../stylesheets"
sass_dir = "."

Put your sass templates in WEB-INF/sass and each request for a css file will regenerate as needed.

The first 3 nodes of the version will match the version of sass that is being used. Current versions of sass and compass can be found in the Gemfile.

Configuration is done through a combination of filter init parameters and the config.rb file. The following filter init parameters are available to control the execution of the filter:

• configLocation - the location of the config.rb (default WEB-INF/sass/config.rb)
• onlyRunWhenKey - the system property or environment variable to check to see if sass compilation should run, use this to turn sass generation off in production
• onlyRunWhenValue - the corresponding value to check to see if sass compilation should run

A common practice is to turn sass generation off in production and precompile in your build process. An example of how to do this based off a system property is:

<filter>
    <filter-name>SassCompiler</filter-name>
    <filter-class>com.darrinholst.sass_java.SassCompilingFilter</filter-class>
    <init-param>
        <param-name>onlyRunWhenKey</param-name>
        <param-value>RUNTIME_ENVIRONMENT</param-value>
    </init-param>
    <init-param>
        <param-name>onlyRunWhenValue</param-name>
        <param-value>local</param-value>
    </init-param>
</filter>

With this configuration the filter will check a system property or environment variable called RUNTIME_ENVIRONMENT and only run the sass compilation if that value is equal to local

See the compass config documentation to find out about all the wonderful things you can put in config.rb. For those config options that reference a file or directory, the working directory that compass will be executed in is the directory that contains config.rb.

Use the maven plugin

The magic behind how this works comes from packaging up the sass gems into a jar that the filter can then use via jruby. The process to jar up the gems is described here. That process is mavenized here. So to change sass or compass versions All Ya Gotta Do™ is update the Gemfile and mvn clean install.

First time? Read this
mvn release:prepare release:perform
That worked? Read this

1. git clone https://github.com/darrinholst/sass-java.git
2. cd sass-java
3. mvn install
4. mvn jetty:run -pl sass-java
5. open http://localhost:8080
6. change src/test/sample-webapp/WEB-INF/sass/application.scss
7. refresh