The Runnable FileSystem Resource is just like a file system resource, with the addition that, when configured as input to a reloadable service, it will call code that you supply prior to checking whether the service needs to be refreshed. This gives you the ability to be involved prior to a service being updated.
There is no custom syntax available to configure this resource. The class name is net.shibboleth.ext.spring.resource.RunnableFileSystemResource. It has all the same methods as the standard Spring FileSystemResource, but the constructors are different, taking a second parameter with name "runnable"
The injected class "runnable" (which has to implement java.lang.Runnable) is expected to update the file if required. It could
Connect to a database to refresh the file
Reach across the network (using a protocol other than HTTP) to refresh the resource
This class, when injected into a RunnableFileSystemResource, allows a script to be run as part of a ReloadableService refresh. There are only two properties which can be set: "script" an EvaluableScript to be run and "customObject".
<bean id="Script" class="net.shibboleth.utilities.java.support.scripting.EvaluableScript" c:_0="
var i = 22;
var j = 7;
var pi = i/j;"/>
<bean id="Runnable" class="net.shibboleth.utilities.java.support.scripting.ScriptedRunnable" p:script-ref="Script" init-method="initialize"/>
<bean id="Resource" class="net.shibboleth.ext.spring.resource.RunnableFileSystemResource" c:path="file" c:runnable-ref="Runnable"/>