如何从Sesame服务器中添加和检索数据

Question

我熟悉芝麻三重存储和尝试基本的东西，如添加和检索数据。当我使用SailRepository时，一切都工作得很好，但是当我使用如下所示的http存储库时，我得到这个错误:

 repository initialized
    Exception in thread "main" org.openrdf.repository.http.HTTPQueryEvaluationException: 
        at org.openrdf.repository.http.HTTPTupleQuery.evaluate(HTTPTupleQuery.java:59)
        at servlet.sesame.Test.isStored(Test.java:28)
        at servlet.sesame.Test.ADD(Test.java:33)
    at servlet.sesame.Test.main(Test.java:54)
Caused by: org.openrdf.repository.RepositoryException: 
    at org.openrdf.http.client.HTTPClient.handleHTTPError(HTTPClient.java:953)
    at org.openrdf.http.client.HTTPClient.sendTupleQueryViaHttp(HTTPClient.java:718)
    at org.openrdf.http.client.HTTPClient.getBackgroundTupleQueryResult(HTTPClient.java:602)
    at org.openrdf.http.client.HTTPClient.sendTupleQuery(HTTPClient.java:367)
    at org.openrdf.repository.http.HTTPTupleQuery.evaluate(HTTPTupleQuery.java:53)
    ... 3 more

下面是我的代码:

public class Test {

public static boolean isStored(String id, Repository rep) throws RepositoryException, QueryEvaluationException, MalformedQueryException
{
    ValueFactory f = rep.getValueFactory();
    URI testedIdURI = f.createURI("http://example.org/" + id);
    // Check if
    String request ="SELECT ?subject WHERE{<"+ testedIdURI +"> ?predicate ?object}";
    TupleQueryResult reponse = rep.getConnection().prepareTupleQuery(QueryLanguage.SPARQL, request).evaluate();
    return reponse.hasNext();
}
public static void ADD(String id, Repository rep) throws RepositoryException, QueryEvaluationException, MalformedQueryException{
    boolean is = isStored(id,rep);
    if(is){
        System.out.println("already exists");
    }
    else{
        rep.getConnection().add(rep.getValueFactory().createURI("http://example.org/", id), RDF.TYPE,FOAF.PERSON);
        System.out.println(id+" added");
    }
}

public static void main(String[] args) throws RepositoryException,RDFHandlerException, MalformedQueryException, QueryEvaluationException {
    Repository rep = new HTTPRepository("http://localhost:8080/openrdf-workbench/","Test");
    //Repository rep = new SailRepository(new MemoryStore());
    rep.initialize();
    System.out.println("repository initialized");

    ValueFactory f = rep.getValueFactory();
    try{
        ADD("Timon",rep);
        ADD("Pumba",rep);
        ADD("eddy",rep);
        ADD("Pumba",rep);
        ADD("Timon",rep);
    rep.getConnection().add(f.createURI("http://example.org/", "Turin"),RDF.PREDICATE,f.createURI("http://example.org/", "Timon"));
    rep.getConnection().add(f.createURI("http://example.org/", "Turin"),RDF.PREDICATE,f.createURI("http://example.org/", "Timon"));
    rep.getConnection().add(f.createURI("http://example.org/", "Timon"),RDF.PREDICATE, f.createURI("http://example.org/", "eddy"));
    rep.getConnection().add(f.createURI("http://example.org/", "Pumba"),RDF.PREDICATE, f.createURI("http://example.org/", "Timon"));

//  RepositoryResult<Statement> statements = rep.getConnection().getStatements(null, null, null, true);
//  Model model = Iterations.addAll(statements, new LinkedHashModel());
    String request = "SELECT DISTINCT ?object WHERE{<" +f.createURI("http://example.org/", "Timon")+"> <"+ RDF.PREDICATE +"> ?object }";
    rep.getConnection().prepareTupleQuery(QueryLanguage.SPARQL, request);
    TupleQueryResult res = rep.getConnection().prepareTupleQuery(QueryLanguage.SPARQL, request).evaluate();
    String s="";
    while(res.hasNext())
    {
        BindingSet bs = res.next();
        s+="n " +(bs.getBinding("object").getValue().stringValue());
    }
    System.out.println(s);
}
    finally 
    {
        rep.getConnection().close();
    }
}
}

Answer 1

您的代码有几处错误。当前的问题可能是由这一行引起的:

Repository rep = new HTTPRepository("http://localhost:8080/openrdf-workbench/","Test");

您在这里使用了错误的服务器URL。正确的服务器URL为http://localhost:8080/openrdf-sesame/。

除此之外，我还有一个技巧可以让你的代码更健壮、更快、更可伸缩。在代码中，您在方法之间传递Repository对象，并在每次执行更新或查询时创建一个新的RepositoryConnection。这确实是非常低效的，更不用说这样就不会关闭任何连接了。

因此，我建议您重用RepositoryConnection对象，并在完成后适当地关闭它。例如，而不是:

    rep.getConnection().add(f.createURI("http://example.org/", "Turin"),RDF.PREDICATE,f.createURI("http://example.org/", "Timon"));
rep.getConnection().add(f.createURI("http://example.org/", "Turin"),RDF.PREDICATE,f.createURI("http://example.org/", "Timon"));
rep.getConnection().add(f.createURI("http://example.org/", "Timon"),RDF.PREDICATE, f.createURI("http://example.org/", "eddy"));
rep.getConnection().add(f.createURI("http://example.org/", "Pumba"),RDF.PREDICATE, f.createURI("http://example.org/", "Timon"));

执行如下操作:

RepositoryConnection conn = rep.getConnection(); 
try {
   conn.begin(); // start a transaction 
   conn.add(f.createURI("http://example.org/", "Turin"),RDF.PREDICATE,f.createURI("http://example.org/", "Timon"));
   conn.add(f.createURI("http://example.org/", "Turin"),RDF.PREDICATE,f.createURI("http://example.org/", "Timon"));
   conn.add(f.createURI("http://example.org/", "Timon"),RDF.PREDICATE, f.createURI("http://example.org/", "eddy"));
   conn.add(f.createURI("http://example.org/", "Pumba"),RDF.PREDICATE, f.createURI("http://example.org/", "Timon"));
   conn.commit(); 
 } 
 finally {
    conn.close();
 }