How to fix custom function class not registered in apache jena fuseki error?

Question

I need a custom filter function in apache-jena-fuseki. I tried adding custom function class name to config.ttl. I added function class files to class path. But it's always throwing error that function is not registered.

Can anyone please share a detailed approach I can try or some documentation? Desperately need it.

Added following line To Configuration File

[] ja:loadClass "org.apache.jena.sparql.function.library.function" .

Class file is in folder /home/user/custom_functions/

Class file package name = org.apache.jena.sparql.function.library.

Java command to launch fuseki server is

java -cp /home/user/custom_functions/function.class:/home/user/apache-jena-4.5.0/lib-src/*:/home/user/apache-jena-4.5.0/lib/* -jar fuseki-server.jar

Function takes one argument. When I run query, it gives me error log that function has not registered FunctionFactory.

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX java: <http://www.w3.org/2007/uwa/context/java.owl#>
PREFIX f: <java:org.apache.jena.sparql.function.library.>
SELECT ?s ?o { 
    ?s rdfs:label ?o . 
    FILTER (f:function(?o) ) .
}