Hibernate NullPointerException In Loader Class

Question

I'm having a bit of an odd problem. This is Hibernate 3.3.2-GA with DB2400Dialect. I'm seeing the following exception --

java.lang.NullPointerException
at org.hibernate.loader.Loader.doQuery(Loader.java:720)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:259)
at org.hibernate.loader.Loader.doList(Loader.java:2232)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2129)
at org.hibernate.loader.Loader.list(Loader.java:2124)
at org.hibernate.loader.custom.CustomLoader.list(CustomLoader.java:312)
at org.hibernate.impl.SessionImpl.listCustomQuery(SessionImpl.java:1723)
at org.hibernate.impl.AbstractSessionImpl.list(AbstractSessionImpl.java:165)
at org.hibernate.impl.SQLQueryImpl.list(SQLQueryImpl.java:175)
at com.example.WidgetDao.getAllWidgets(WidgetDao.java:28)
at com.example.TestWidgetDao.testGetAllWidgets(TestWidgetDao.java:12)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:79)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:618)
at org.junit.internal.runners.TestMethodRunner.executeMethodBody(TestMethodRunner.java:99)
at org.junit.internal.runners.TestMethodRunner.runUnprotected(TestMethodRunner.java:81)
at org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
at org.junit.internal.runners.TestMethodRunner.runMethod(TestMethodRunner.java:75)
at org.junit.internal.runners.TestMethodRunner.run(TestMethodRunner.java:45)
at org.junit.internal.runners.TestClassMethodsRunner.invokeTestMethod(TestClassMethodsRunner.java:66)
at org.junit.internal.runners.TestClassMethodsRunner.run(TestClassMethodsRunner.java:35)
at org.junit.internal.runners.TestClassRunner$1.runUnprotected(TestClassRunner.java:42)
at org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
at org.junit.internal.runners.TestClassRunner.run(TestClassRunner.java:52)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:45)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

The testGetAllWidgets() method is calling WidgetDao.getAllWidgets() twice in a row. The first call works perfectly fine. The result set and mapped objects returned are exactly as I expect. However, I call getAllWidgets() immediately again and the above NPE is thrown. I've tracked it down a bit deeper and the following line in Loader.java is returning a null result set --

// Line 1809 in     
rs = session.getBatcher().getResultSet( (CallableStatement) st, dialect );

The DAO method is executed a stored procedure defined via in the mapping document.

I'm really stumped here. I've literally mapped a few dozen classes to different stored procedures. Suddenly this one has decided to give me fits. There's nothing special about the proc and it simply returns a few String columns.

Anyone have an idea how to track this down further?

Thanks!

Answer 1

This is more likely then not a problem with DB2 JDBC driver.

Put a breakpoint in DB2Dialect.getResultSet() method and check the ResultSet you're getting there. Perhaps it's trying to be smart and cache the CallableStatement and something goes awry.

When you say "call it immediately again" do you really mean "immediately" - e.g. within the same session? Does it work in a new session (it should)? If you don't find a JDBC-level solution (some connection parameter to turn caching off), that maybe an alternative solution.