Jena JavaScript custom functions scriptEngine null error - jena

Question

Summary: I am trying to use the documentation on JavaScript SPARQL Functions to get a minimal working example of calling a custom javascript function, but it results in a scriptEngine null error.
Details: I setup a fuseki environment following the Docker instructions, so:
docker build --force-rm --build-arg JENA_VERSION=3.16.0 -t fuseki .
I then create a functions.js file per the documentation on JavaScript SPARQL Functions and launch the Docker container with:
docker run -i --rm -p "3030:3030" --name sparql1 -v `pwd`/functions.js:/functions.js -t fuseki --update --set arq:js-library=/functions.js --mem /ds
So far, so good. I have confirmed this works for simple update and queries, so the container appears sound. However, if I now create a query.rq file containing the example in the docs:
query=PREFIX js: <http://jena.apache.org/ARQ/jsFunction#>
SELECT ?input (js:toCamelCase(?input) AS ?X)
{
VALUES ?input { "some woRDs to PROCESS" }
}
and then proceed to dispatch this query to my container:
curl -X POST -d #query.rq localhost:3030/ds/query
then the console in which the container is running looks as follows:
% docker run -i --rm -p "3030:3030" --name sparql1 -v `pwd`/functions.js:/functions.js -t fuseki --update --set arq:js-library=/functions.js --mem /ds
[2022-03-09 16:47:20] INFO Server :: Apache Jena Fuseki 3.16.0
[2022-03-09 16:47:20] INFO Server :: Dataset Type: in-memory
[2022-03-09 16:47:20] INFO Server :: Path = /ds
[2022-03-09 16:47:20] INFO Server :: System
[2022-03-09 16:47:20] INFO Server :: Memory: 2.0 GiB
[2022-03-09 16:47:20] INFO Server :: Java: 17-ea
[2022-03-09 16:47:20] INFO Server :: OS: Linux 5.10.76-linuxkit amd64
[2022-03-09 16:47:20] INFO Server :: PID: 1
[2022-03-09 16:47:20] INFO Server :: Start Fuseki (port=3030)
[2022-03-09 16:47:23] INFO Fuseki :: [1] POST http://localhost:3030/ds/query
[2022-03-09 16:47:23] INFO Fuseki :: [1] Query = PREFIX js: <http://jena.apache.org/ARQ/jsFunction#>SELECT ?input (js:toCamelCase(?input) AS ?X){ VALUES ?input { "some woRDs to PROCESS" }}
[2022-03-09 16:47:24] WARN Fuseki :: [1] RC = 500 : Cannot invoke "javax.script.ScriptEngine.eval(java.io.Reader)" because "scriptEngine" is null
java.lang.NullPointerException: Cannot invoke "javax.script.ScriptEngine.eval(java.io.Reader)" because "scriptEngine" is null
at org.apache.jena.sparql.function.js.JSEngine.build(JSEngine.java:75) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.function.js.JSEngine.<init>(JSEngine.java:61) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.function.js.EnvJavaScript.build(EnvJavaScript.java:103) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.function.js.EnvJavaScript.<init>(EnvJavaScript.java:99) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.function.js.EnvJavaScript.create(EnvJavaScript.java:52) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.function.js.EnvJavaScript.get(EnvJavaScript.java:66) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.expr.E_Function.evalSpecial(E_Function.java:66) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.expr.ExprFunctionN.eval(ExprFunctionN.java:100) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.core.VarExprList.get(VarExprList.java:106) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.iterator.QueryIterAssign.accept(QueryIterAssign.java:62) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.iterator.QueryIterProcessBinding.hasNextBinding(QueryIterProcessBinding.java:69) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:114) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.iterator.QueryIterConvert.hasNextBinding(QueryIterConvert.java:58) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:114) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:38) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:114) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:38) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:114) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.ResultSetStream.hasNext(ResultSetStream.java:74) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.sparql.engine.ResultSetCheckCondition.hasNext(ResultSetCheckCondition.java:55) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.SPARQLQueryProcessor.executeQuery(SPARQLQueryProcessor.java:324) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.SPARQLQueryProcessor.execute(SPARQLQueryProcessor.java:273) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.SPARQLQueryProcessor.executeWithParameter(SPARQLQueryProcessor.java:222) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.SPARQLQueryProcessor.execute(SPARQLQueryProcessor.java:207) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.ActionService.executeLifecycle(ActionService.java:58) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.SPARQLQueryProcessor.execPost(SPARQLQueryProcessor.java:83) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.ActionProcessor.process(ActionProcessor.java:34) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.ActionBase.process(ActionBase.java:55) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.ActionExecLib.execAction(ActionExecLib.java:107) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.server.Dispatcher.dispatchAction(Dispatcher.java:115) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.server.Dispatcher.process(Dispatcher.java:107) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.server.Dispatcher.dispatch(Dispatcher.java:101) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.apache.jena.fuseki.servlets.FusekiFilter.doFilter(FusekiFilter.java:51) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1604) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:545) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:233) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1297) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:188) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:485) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:186) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1212) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:127) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.Server.handle(Server.java:500) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.HttpChannel.lambda$handle$1(HttpChannel.java:383) ~[jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:547) [jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:375) [jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:270) [jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:311) [jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:103) [jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:117) [jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:806) [jena-fuseki-server-3.16.0.jar:3.16.0]
at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:938) [jena-fuseki-server-3.16.0.jar:3.16.0]
at java.lang.Thread.run(Unknown Source) [?:?]
[2022-03-09 16:47:24] INFO Fuseki :: [1] 500 Cannot invoke "javax.script.ScriptEngine.eval(java.io.Reader)" because "scriptEngine" is null (212 ms)
It's at this point I'm totally lost ... why would scriptEngine be null here?

Answer 1

In Apache Jena 3.16.0, the JS engine was Nashorn. Nashorn was deprecated in Java 11 and removed in Java17.
An earlier Java version will have Hashorn in.
Now Jena version 4.4.0 uses the javascript engine of choice which has been added to the classpath, and hence needs to be in the dockerfile. Jena testing uses GraalVM.

Answer 2

I accepted the answer by #AndyS above because it helped me solve the problem. For anyone who comes across this and wants to know the full details I'm posting this additional detail.
Basically, I ignored the "official" docker compose script since it uses OpenJDK and instead created a simple Dockerfile based on one of the official GraalVM containers. I just needed to add the GraalVM nodejs so that it has a JavaScript interpreter, giving full Dockerfile as follows:
FROM ghcr.io/graalvm/graalvm-ce:ol8-java17-22.0.0.2-b2
RUN gu install nodejs
RUN curl -s -S --fail --location --max-redirs 3 https://repo1.maven.org/maven2/org/apache/jena/jena-fuseki-server/4.4.0/jena-fuseki-server-4.4.0.jar --output jena-fuseki-server-4.4.0.jar
RUN adduser -M fuseki
USER fuseki
EXPOSE 3030
ENTRYPOINT ["java", "-jar", "jena-fuseki-server-4.4.0.jar"]
CMD []
Now, you can build this with:
docker build -t fuseki .
And then run it and include the functions.js file from the original question with:
docker run -it --rm -p "3030:3030" --name sparql1 -v $(pwd)/functions.js:/functions.js fuseki --update --set arq:js-library=/functions.js --mem /ds
Now, posting the query from the question above gives the correct output:
% curl -X POST -d #query.rq localhost:3030/ds/query
{ "head": {
"vars": [ "input" , "X" ]
} ,
"results": {
"bindings": [
{
"input": { "type": "literal" , "value": "some woRDs to PROCESS" } ,
"X": { "type": "literal" , "value": "someWordsToProcess" }
}
]
}
}
Again, thanks to #AndyS without whose comment this full solution would have evaded me!