config-default.json file missing ?

[rom1504]

QueryResultsWriter main want a config-default.json file and it's not in the repo.

What should be in that config file ?

[RubenVerborgh]

My guess is this would be like config-default.json from the JavaScript client. Basically, it mentions a default start fragment and prefixes.

Agree that this should be in the package though. @laurensdv, can you verify?

[rom1504]

Hmm apparently there's actually a https://github.com/LinkedDataFragments/Client.Java/blob/master/src/main/conf/config-default.json .

I'm not sure what are the parameter of that main actually, it seems the query parameter is actually a file ?
What format should be that file ?

I'm trying to make something work, because I'm having other problem if I simply try to add it to my projet through maven (using mvn install:install-file -Dfile=Client.Java/target/ldf-client-jar-with-dependencies.jar -DgroupId=org.linkeddatafragments -DartifactId=ldf-client -Dversion=0.1-SNAPSHOT -Dpackaging=jar since it's not (yet ?) published in some maven repo) :

I'm getting "Exception in thread "main" java.lang.NoSuchFieldError: INSTANCE" which seems to be coming from httpasyncclient or something..

[rom1504]

If I make a file query containing only SELECT distinct ?o WHERE { <http://dbpedia.org/resource/Bill_Clinton> <http://dbpedia.org/ontology/child> ?o } and then try to run java -jar target/ldf-client-jar-with-dependencies.jar query, I get :

java.lang.IllegalArgumentException: URI to read from is null
        at org.apache.jena.riot.RDFDataMgr.parse(RDFDataMgr.java:644)
        at org.apache.jena.riot.RDFDataMgr.read(RDFDataMgr.java:211)
        at org.apache.jena.riot.RDFDataMgr.read(RDFDataMgr.java:184)
        at org.apache.jena.riot.RDFDataMgr.read(RDFDataMgr.java:122)
        at org.apache.jena.riot.RDFDataMgr.read(RDFDataMgr.java:113)
        at org.apache.jena.riot.adapters.RDFReaderRIOT.read(RDFReaderRIOT.java:77)
        at com.hp.hpl.jena.rdf.model.impl.ModelCom.read(ModelCom.java:247)
        at org.linkeddatafragments.client.LinkedDataFragmentsClient.getBaseFragment(LinkedDataFragmentsClient.java:58)
        at org.linkeddatafragments.model.LinkedDataFragmentGraph.graphBaseFind(LinkedDataFragmentGraph.java:71)
        at com.hp.hpl.jena.graph.impl.GraphBase.find(GraphBase.java:268)
        at com.hp.hpl.jena.graph.impl.GraphBase.graphBaseFind(GraphBase.java:290)
        at com.hp.hpl.jena.graph.impl.GraphBase.find(GraphBase.java:287)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterTriplePattern$TripleMapper.<init>(QueryIterTriplePattern.java:80)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterTriplePattern.nextStage(QueryIterTriplePattern.java:53)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterRepeatApply.makeNextStage(QueryIterRepeatApply.java:115)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterRepeatApply.hasNextBinding(QueryIterRepeatApply.java:67)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterBlockTriples.hasNextBinding(QueryIterBlockTriples.java:64)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterConvert.hasNextBinding(QueryIterConvert.java:59)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIterDistinctReduced.hasNextBinding(QueryIterDistinctReduced.java:54)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:40)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:40)
        at com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:112)
        at com.hp.hpl.jena.sparql.engine.ResultSetStream.hasNext(ResultSetStream.java:75)
        at org.linkeddatafragments.client.QueryResultsWriter.writeResults(QueryResultsWriter.java:52)
        at org.linkeddatafragments.client.QueryResultsWriter.main(QueryResultsWriter.java:114)

[RubenVerborgh]

I was just told by @mielvds that he has a local version that is more advanced than the tree here. It addresses most of the issues you mention, so I'll leave it to him to follow up.

[rom1504]

I managed to make the main of QueryResultsWriter work by using the config-default.json in the repo, but I think it should use that one automatically when no config file is given (using maven resources maybe ?).

Using the project as a dependency from my project still gives me these errors :

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/people/beaumont/.m2/repository/org/slf4j/slf4j-log4j12/1.7.6/slf4j-log4j12-1.7.6.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/people/beaumont/.m2/repository/org/linkeddatafragments/ldf-client/0.1-SNAPSHOT/ldf-client-0.1-SNAPSHOT.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]
Exception in thread "main" java.lang.NoSuchFieldError: INSTANCE
    at org.apache.http.impl.nio.codecs.DefaultHttpRequestWriterFactory.<init>(DefaultHttpRequestWriterFactory.java:52)
    at org.apache.http.impl.nio.codecs.DefaultHttpRequestWriterFactory.<init>(DefaultHttpRequestWriterFactory.java:56)
    at org.apache.http.impl.nio.codecs.DefaultHttpRequestWriterFactory.<clinit>(DefaultHttpRequestWriterFactory.java:46)
    at org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionFactory.<init>(ManagedNHttpClientConnectionFactory.java:75)
    at org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionFactory.<init>(ManagedNHttpClientConnectionFactory.java:83)
    at org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionFactory.<clinit>(ManagedNHttpClientConnectionFactory.java:64)
    at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager$InternalConnectionFactory.<init>(PoolingNHttpClientConnectionManager.java:519)
    at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.<init>(PoolingNHttpClientConnectionManager.java:161)
    at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.<init>(PoolingNHttpClientConnectionManager.java:145)
    at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.<init>(PoolingNHttpClientConnectionManager.java:117)
    at org.apache.http.impl.nio.client.HttpAsyncClientBuilder.build(HttpAsyncClientBuilder.java:605)
    at org.apache.http.impl.nio.client.HttpAsyncClients.createDefault(HttpAsyncClients.java:62)
    at org.linkeddatafragments.client.LinkedDataFragmentsClient.<init>(LinkedDataFragmentsClient.java:37)
    at org.linkeddatafragments.model.LinkedDataFragmentGraph.<init>(LinkedDataFragmentGraph.java:38)
    at client.JenaDBpediaClient.main(JenaDBpediaClient.java:15)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)

I'm just trying to make some basic thing work using the code from the README and some jena example :

public static void main(String[] args)
    {
        LinkedDataFragmentGraph ldfg = new LinkedDataFragmentGraph("http://data.linkeddatafragments.org/dbpedia");
        Model model = ModelFactory.createModelForGraph(ldfg);
        String queryString = "SELECT distinct ?o WHERE { <http://dbpedia.org/resource/Bill_Clinton> <http://dbpedia.org/ontology/child> ?o }" ;
        Query query = QueryFactory.create(queryString) ;
        try (QueryExecution qexec = QueryExecutionFactory.create(query, model)) {
            ResultSet results = qexec.execSelect() ;
            for ( ; results.hasNext() ; )
            {
                QuerySolution soln = results.nextSolution() ;
                //RDFNode x = soln.get("varName") ;       // Get a result variable by name.
                Resource r = soln.getResource("VarR") ; // Get a result variable - must be a resource
                //Literal l = soln.getLiteral("VarL") ;   // Get a result variable - must be a literal
                System.out.println(r);
            }
        }
    }

The error is actually on the first line (the new LinkedDataFragmentGraph).

I think it would be nice to have a (working) simple such example on the README.

[rom1504]

I managed to make something work by removing the up to date jena from my project and using the one LinkedDataFragments has and by changing the code a bit for that older jena version :

public static void main(String[] args)
    {
        LinkedDataFragmentGraph ldfg = new LinkedDataFragmentGraph("http://data.linkeddatafragments.org/dbpedia");
        Model model = ModelFactory.createModelForGraph(ldfg);
        String queryString = "SELECT distinct ?o WHERE { <http://dbpedia.org/resource/Bill_Clinton> <http://dbpedia.org/ontology/child> ?o }" ;
        Query query = QueryFactory.create(queryString) ;
        QueryExecution qexec = QueryExecutionFactory.create(query, model);
        ResultSet results = qexec.execSelect() ;
        for ( ; results.hasNext() ; )
        {
            QuerySolution soln = results.next() ;
            System.out.println(soln);
        }
    }

I'm not sure if this is a good way to use it though, it's slower than QueryResultsWriter and the loop doesn't seem to end.

[rom1504]

Ok it just takes some times to initialize ldfg and model, but the querying is fast. Apparently a System.exit(0); is needed at the end of the main for it to exit, so the loop is ok.

So in short :

• jena needs to be updated (as in Updated to Apache Jena 2.12.1 #2 I guess)
• the main of QueryResultsWriter needs to handle the user not giving a config file
• it would be nice to have a small example in the README on how to use it
• publishing the lib on a maven repo would make it easier to use

But anyway, it works ! Thanks for this lib, LinkedDataFragments really seems like a good idea !

[RubenVerborgh]

@mielvds @laurensdv Any action still needed for this one? If not, please close.

[mielvds]

There are indeed some issues. I guess https://github.com/LinkedDataFragments/Client.Java/blob/master/src/main/java/org/linkeddatafragments/client/QueryResultsWriter.java#L80 will have to change, amongst others. I'll keep this open for now