Re: NullPointerException, how to determine cause?

[Alex Kravets]

I am sure this part works, because if comment out try block everything 
works fine. But If the cause of exception is the code in try block, how 
come catch does not work?

Pavel Kolesnikov wrote:
I guess the only plase where NPE may occure is the line:
        String sqlQuery = ((ExecuteQueryForm) form).getSQLQuery();
Are you sure there's a form definition available for this action?
It means, is there a "name" attribute defined in an appropriate <action>
element in your struts-config.xml?
Pavel
On Wed, 19 Jan 2005 12:34:51 -0500, Alex Kravets
<[EMAIL PROTECTED]> wrote:
 

I am trying to connect to a database in Action Class and set return data
into a vector. Then vector is set into session and session is read from
forwarded page. However, I am getting NullPointerException. Now I put
the part of the code that I think might generate an exception into try
block, but no luck same exception. In addition, stack trace does not
seem to give the line of perform() where error occurs.
SEVERE: Servlet.service() for servlet action threw exception
java.lang.NullPointerException
       at app.ExecuteQueryAction.perform(Unknown Source)
       at
org.apache.struts.action.ActionServlet.processActionPerform(ActionServlet.java:1787)
       at
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1586)
       at
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:510)
       at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
       at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
       at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
       at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
       at
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)
       at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
       at
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
       at
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
       at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
       at
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
       at
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:825)
       at
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:731)
       at
org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:526)
       at
org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
       at
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
       at java.lang.Thread.run(Thread.java:595)
and Action Class:
package app;
import java.io.IOException;
import java.util.Vector;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionError;
import org.apache.struts.action.ActionErrors;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionServlet;
import com.kwi.DBDriver;
public final class ExecuteQueryAction extends Action {
   public ActionForward perform(ActionMapping mapping,
           ActionForm form,
           HttpServletRequest request,
           HttpServletResponse response)
       throws IOException, ServletException {
       // Obtain username and password from web tier
       String sqlQuery = ((ExecuteQueryForm) form).getSQLQuery();
       Vector v = new Vector();
       HttpSession session = request.getSession();
       try{
               v = DBDriver.doSelect("generic2",sqlQuery);
               v.add("test");
               session.setAttribute("output",v);
       }
       catch(NullPointerException nle){
               v.add("no good");
               session.setAttribute("output",v);
       }
       session.setAttribute("query",form);
       // Return success
       return mapping.findForward("success");
   }
} // End LogonAction
thanks,
Alex
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