Jena Fuseki Client

Question

I'm trying to write a simple Jena Fuseki client in Java to send a SELECT SPARQL query and get the result.

I've found the following code written by someone else. It keeps crashing at runtime.

I'm using jena-arq-3.1.0.jar

javac -cp .;jena-arq-3.1.0.jar Main.java print no errors

java -cp .;jena-arq-3.1.0.jar Main crash!

Error log

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/jena/atlas/io/Printable
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(Unknown Source)
        at java.security.SecureClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.access$100(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at org.apache.jena.query.QueryFactory.create(QueryFactory.java:78)
        at org.apache.jena.query.QueryFactory.create(QueryFactory.java:52)
        at org.apache.jena.query.QueryFactory.create(QueryFactory.java:40)
        at Main.main(Main.java:24)
Caused by: java.lang.ClassNotFoundException: org.apache.jena.atlas.io.Printable
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 16 more

Main.java

import java.net.URL;
import java.util.List; 

import org.apache.jena.query.Query; 
import org.apache.jena.query.QueryExecution; 
import org.apache.jena.query.QueryExecutionFactory; 
import org.apache.jena.query.QueryFactory; 
import org.apache.jena.query.QuerySolution; 
import org.apache.jena.query.ResultSet; 

class Main { 

    public static void main(final String[] args) throws Exception { 
        String queryString=
        "prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>"+
        "prefix owl: <http://www.w3.org/2002/07/owl#>"+

        "SELECT ?subject ?predicate ?object"+
        "WHERE {"+
        " ?subject ?predicate ?object"+
        " } LIMIT 25";

        // now creating query object
        Query query = QueryFactory.create(queryString);
        // initializing queryExecution factory with remote service.
        // **this actually was the main problem I couldn't figure out.**
        QueryExecution qexec = QueryExecutionFactory.sparqlService("http://localhost:3030/FirstEndpoint/sparql", query);

        //after it goes standard query execution and result processing which can
        // be found in almost any Jena/SPARQL tutorial.
        try {
            ResultSet results = qexec.execSelect();
            for (; results.hasNext();) {

            // Result processing is done here.
            }
        }
        finally {
           qexec.close();
        }
    } 

}

Answer 1

You need all necessary libs in the classpath, not only jena-arq .

javac works because you're using only classes from the jena-arq JAR. java doesn't work because at runtime the classes of ARQ refer to other classes contain eg in jena-core, jena-iri, etc.

The easiest way would to add all libs from the Jena distribution resp. the lib folder itself to the classpath.