Scrollable cursor bug?

Question

Hello,
When I first start my application from jdeveloper, I get this exception... Only once: when I do a "refresh", the application works normally and never gives the problem until the next server restart...
500 Internal Server Error
java.lang.NullPointerException     at java.lang.Class.forName0(Native Method)     at java.lang.Class.forName(Class.java:164)     at oracle.jdbc.driver.PhysicalConnection.safelyGetClassForName(PhysicalConnection.java:4583)     at oracle.jdbc.driver.PhysicalConnection.addClassMapEntry(PhysicalConnection.java:2737)     at oracle.jdbc.driver.PhysicalConnection.addDefaultClassMapEntriesTo(PhysicalConnection.java:2728)     at oracle.jdbc.driver.PhysicalConnection.initializeClassMap(PhysicalConnection.java:2456)     at oracle.jdbc.driver.PhysicalConnection.ensureClassMapExists(PhysicalConnection.java:2450)     at oracle.jdbc.driver.PhysicalConnection.getTypeMap(PhysicalConnection.java:2714)     at oracle.jdbc.driver.ScrollableResultSet.getObject(ScrollableResultSet.java:742)     at oracle.toplink.oraclespecific.Oracle9Platform.getObjectFromResultSet(Oracle9Platform.java:152)     at oracle.toplink.internal.databaseaccess.DatabaseAccessor.getObject(DatabaseAccessor.java:963)     at oracle.toplink.internal.databaseaccess.DatabaseAccessor.fetchRow(DatabaseAccessor.java:771)     at oracle.toplink.internal.databaseaccess.DatabaseAccessor.cursorRetrieveNextRow(DatabaseAccessor.java:352)     at oracle.toplink.queryframework.ScrollableCursor.retrieveNextObject(ScrollableCursor.java:512)     at oracle.toplink.queryframework.ScrollableCursor.loadNext(ScrollableCursor.java:357)     at oracle.toplink.queryframework.ScrollableCursor.hasNext(ScrollableCursor.java:233)     at be.uclouvain.doctorats.dao.factories.GenericFactory.searchAll(GenericFactory.java:198)     at be.uclouvain.doctorats.business.GenericBusiness.searchAll(GenericBusiness.java:188)     at be.uclouvain.doctorats.business.GenericBusiness.searchAllFromParent(GenericBusiness.java:393)     at be.uclouvain.doctorats.business.utils.Interlocutor.listObjects(Interlocutor.java:194)     at be.uclouvain.doctorats.action.ListAction.doAction(ListAction.java:55)     at be.uclouvain.doctorats.action.BasicAction.execute(BasicAction.java:46)     at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)     at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)     at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)     at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:507)     at javax.servlet.http.HttpServlet.service(HttpServlet.java:743)     at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)     at com.evermind[Oracle Containers for J2EE 10g (10.1.3.1.0) ].server.http.ServletRequestDispatcher.invoke(ServletRequestDispatcher.java:711)     at com.evermind[Oracle Containers for J2EE 10g (10.1.3.1.0) ].server.http.ServletRequestDispatcher.forwardInternal(ServletRequestDispatcher.java:368)     at com.evermind[Oracle Containers for J2EE 10g (10.1.3.1.0) ].server.http.HttpRequestHandler.doProcessRequest(HttpRequestHandler.java:866)     at com.evermind[Oracle Containers for J2EE 10g (10.1.3.1.0) ].server.http.HttpRequestHandler.processRequest(HttpRequestHandler.java:448)     at com.evermind[Oracle Containers for J2EE 10g (10.1.3.1.0) ].server.http.HttpRequestHandler.serveOneRequest(HttpRequestHandler.java:216)     at com.evermind[Oracle Containers for J2EE 10g (10.1.3.1.0) ].server.http.HttpRequestHandler.run(HttpRequestHandler.java:117)     at com.evermind[Oracle Containers for J2EE 10g (10.1.3.1.0) ].server.http.HttpRequestHandler.run(HttpRequestHandler.java:110)     at oracle.oc4j.network.ServerSocketReadHandler$SafeRunnable.run(ServerSocketReadHandler.java:260)     at com.evermind[Oracle Containers for J2EE 10g (10.1.3.1.0) ].util.ReleasableResourcePooledExecutor$MyWorker.run(ReleasableResourcePooledExecutor.java:303)     at java.lang.Thread.run(Thread.java:595)
Here is the code that seems to cause the problem:
ReadAllQuery readQuery = new ReadAllQuery(modelClass);
List<ModelObject> toplinkResults = new ArrayList<ModelObject>();
int chunkSize = 50;
int index = 0;
if (search != null) {
readQuery.setSelectionCriteria(search.getExpression());
chunkSize = search.getPageSize();
index = search.getIndex();
readQuery.useScrollableCursor(chunkSize);
// lecture
ScrollableCursor cursor = (ScrollableCursor)ToplinkFactory.getSession().executeQuery(readQuery);
if (cursor == null) {
throw new Exception("No cursor!");
if (index > 0) {
cursor.absolute(index);
int size = cursor.size();
int displaySize = chunkSize;
// ajuster si page de données n'a pas sa taile max
if (index + displaySize > size) {
displaySize = size - index;
for (int i=0; i < displaySize; i++) {
if (!cursor.hasNext()) {
throw new Exception("Cursor doesn't seem to work properly!");
toplinkResults.add((ModelObject)cursor.next());
I traced the problem to this line:
if (!cursor.hasNext()) {
It looks like a bug to me... Am I doing something wrong, or is it Toplink, or even jdbc???

Answer 1

Ok, it seems to be only there when I run my
application in debug mode in Jdeveloper... When
running it regularly, it works correctly. Is it a
jdev/oc4j bug, or is it a toplink bug which is
triggered in some rare situation, or is it something
else?Thats what you will have to debug further. :-)
When you wrote "running it regularly" did you mean running it through JUnit?
It could be the way you package/load classes in your JDeveloper environment. In order to eliminate the possibility of Toplink causing the bug you could write an identical test case in the app server except you can use JDBC ResultSet.