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Не могли бы вы помочь мне решить проблему, указанную ниже. Я запускаю хранилище triplestore на одном сервере tomcat, а приложение для доступа к хранилищу triplestore на другом сервере tomcat7. Однако в первый раз приложение запускается успешно, если я перезапускаю приложение, а не triplestore, вызывающий проблему с nullpointer.

Ниже приведено исключение, возникающее на сервере triplestore

  SEVERE: Servlet.service() for servlet [ServletAdaptor] in context with path [/triplestore] threw exception [java.lang.NullPointerException] with root cause
 java.lang.NullPointerException
    at com.hp.hpl.jena.sparql.util.NodeUtils$1.accept(NodeUtils.java:
    at com.hp.hpl.jena.sparql.util.NodeUtils$1.accept(NodeUtils.java:91)
    at com.hp.hpl.jena.util.iterator.MapFilterIterator.hasNext(MapFilterIterator.java:55)
    at au.com.triplestore.core.impl.TripleStoreImpl.saveDataset(TripleStoreImpl.java:224)
    at au.com.triplestore.web.TripleStoreRs.saveData(TripleStoreRs.java:323)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:151)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:171)
    at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$ResponseOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:152)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:104)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:402)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:349)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:106)
    at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:259)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:318)
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:236)
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1010)
    at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:373)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:382)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:345)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:220)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org .apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2441)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2430)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:744)
  

И вот код, в котором происходит сбой (строка — while (listOfSavedNames.hasNext()) { )

 public Boolean saveDataset(Model model, String baseUri, Boolean isSave, String reasonerName) {

    dataset.begin(ReadWrite.WRITE);        

    Boolean alreadySaved = false;

    InfModel infModel = null;

    if (baseUri == null) {
        baseUri = model.getNsPrefixURI("ex");
    }

    Iterator<String> listOfSavedNames = dataset.listNames();

    while (listOfSavedNames.hasNext()) { 
        if (baseUri.equals(listOfSavedNames.next())) {
            alreadySaved = true;
            break;
        }
    }


    if (isSave) {
        if (alreadySaved) {

            Model defaultModel = dataset.getDefaultModel();
            Model namedModel = dataset.getNamedModel(baseUri);
            dataset.removeNamedModel(baseUri);



            defaultModel.add(infModel);
            namedModel.add(infModel);
            //Add new model
            dataset.addNamedModel(baseUri, namedModel);

        } else {

            Model defaultModel = dataset.getDefaultModel();
            defaultModel.add(infModel);
            dataset.addNamedModel(baseUri, infModel);
        }
    } else {
        Model defaultModel = dataset.getDefaultModel();
        Model namedModel = dataset.getNamedModel(baseUri);
        dataset.removeNamedModel(baseUri);
        defaultModel.add(infModel);
        namedModel.add(infModel);
        //Add new model
        dataset.addNamedModel(baseUri, namedModel);
    }

    dataset.commit();
    TDB.sync(dataset);
    dataset.end();
    schemaDataset.end();
    return true;

}