using SPARQL Anything as a java library

[justin2004]

I have a Clojure/Java project where I use Apache Jena to run SPARQL constructs.
I'd like to be able to use service clauses with the x-sparql-anything: scheme.

If I don't put the SPARQL Anything jar on the class path and I use Jena to execute this:

PREFIX  fx:   <http://sparql.xyz/facade-x/ns/>
                                    construct {?s ?p ?o}
                                    where {
                                    service <x-sparql-anything:> {
                                    fx:properties fx:location "/tmp/la.json" .
                                    ?s ?p ?o
                                    }}

I get this error (as expected):

Execution error (IllegalArgumentException) at jdk.internal.net.http.common.Utils/newIAE (Utils.java:280).
invalid URI scheme x-sparql-anything

Next, if I put the SPARQL Anything jar on the class path and evaluate this:

(org.apache.jena.sparql.engine.main.QC/setFactory (org.apache.jena.query.ARQ/getContext)
                                                  com.github.sparqlanything.engine.FacadeX/ExecutorFactory)

which is equivalent to:

QC.setFactory(ARQ.getContext(), FacadeX.ExecutorFactory);

Then I execute that construct again I get:

Execution error (QueryExceptionHTTP) at org.apache.jena.sparql.engine.http.HttpQuery/execGet (HttpQuery.java:324).
Malformed URL: java.net.MalformedURLException: unknown protocol: x-sparql-anything

I'd like to know how to tell Apache Jena to use FacadeXOpExecutor when that protocol is encountered. Any tips on how I might do that?

My current guess as to why this isn't working... I think it is related to this... the static initializer in the FacadeX class (which registers functions and magic properties, etc.) might not be getting executed?

[luigi-asprino]

Hi,

I'd like to know how to tell Apache Jena to use FacadeXOpExecutor when that protocol is encountered. Any tips on how I might do that?

It should be this

QC.setFactory(ARQ.getContext(), FacadeX.ExecutorFactory);

The error doesn't seem related to the static initialiser (static block), otherwise, you should get something related to the fact that the engine is not able to find a triplifier for the source.
IMO, the problem is that the operation is not delegated to the FXOpExecutor (maybe because FacadeX.ExecutorFactory is not initialised)
You can try instantiating the OpExecutorFactory explicitly

OpExecutorFactory exFactory = new OpExecutorFactory() {
		@Override
		public OpExecutor create(ExecutionContext execCxt) {
			return new FacadeXOpExecutor(execCxt);
		}
	};

QC.setFactory(ARQ.getContext(), exFactory);

[justin2004]

thanks for the tip, @luigi-asprino .

i tried your suggestion and i got the same error. also, i noticed this...

when the factory is nil

(org.apache.jena.sparql.engine.main.QC/getFactory (org.apache.jena.query.ARQ/getContext)) ; => nil

i get

Execution error (QueryExceptionHTTP) at org.apache.jena.sparql.engine.http.HttpQuery/execGet (HttpQuery.java:324).
Malformed URL: java.net.MalformedURLException: unknown protocol: x-sparql-anything

and when the factory is not nil

(org.apache.jena.sparql.engine.main.QC/getFactory (org.apache.jena.query.ARQ/getContext))
; => #object[com.github.sparqlanything.engine.FacadeX$1 0x5fa0d03 com.github.sparqlanything.engine.FacadeX$1@5fa0d03]

i get the same error as above.

i think i might put a break point here (or somewhere in that file) to see if execution even passes through there when i run a construct.