Null Pointer Exception on stmt = conn.prepareStatement( query);

[JiaPei Jen]

I configured the Tomcat 5.0.27 for using the connection pool feature and connecting to the Oracle. I am testing if I did the configuration correctly. Therefore, I try to retrieve some data from a table. I got the
'Null Pointer Exception" when executing the

         stmt = conn.prepareStatement( query );

I am not sure where the problem is from.
1. configuration is not done properly?
2. some bugs in my program?

I need your help to diagnose the problem. The messages in the Tomcat log are shown below my program coce.

The code for class where the 'Null Pointer Exception' occurred is like:

package org.dhsinfo.message.dao;
 
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.PreparedStatement;
import java.sql.Statement;
import java.sql.SQLException;
 
import org.dhsinfo.message.MemberBean;
import org.dhsinfo.message.exceptions.MemberDAOSysException;
import org.dhsinfo.ConnectionPool.DBConnection;
 
public class OracleMemberDAO implements MemberDAO
{
   // Here the return type is Collection
   public Collection findMembers() 
       throws MemberDAOSysException 
   {
      Connection conn = null;
      PreparedStatement stmt = null;
      ResultSet rs = null;
      MemberBean memberBean;
      Collection members = new ArrayList();
      String query = "SELECT name FROM PersonType"; 
     
      try 
      {
         conn = DBConnection.getDBConnection();
         stmt = conn.prepareStatement( query );  // line number 32
         rs = stmt.executeQuery();
 
 while( rs.next() )
         {
    memberBean = new MemberBean();
            memberBean.setName( rs.getString( "name" ) );
    members.add( memberBean );
         }
         return members;
      }
      catch (SQLException se)
      {
         se.printStackTrace( System.err );
         throw new MemberDAOSysException("SQLException: " + se.getMessage());
      }
      finally
      {
         if ( conn != null )
         {
            try
            {
               rs.close();
               rs = null;
               stmt.close();
               stmt = null;
               conn.close();
            }
            catch( SQLException sqlEx )
            {
               System.out.println( "Problem occurs while closing " + sqlEx );
            }
            conn = null;
         }       
      }
   }
}

java.lang.NullPointerException
at org.dhsinfo.message.dao.OracleMemberDAO.findMembers(OracleMemberDAO.java:32)
at org.dhsinfo.message.MemberService.getMembers(MemberService.java:18)
at org.dhsinfo.message.SendMessage.execute(SendMessage.java:29)
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.doPost(ActionServlet.java:525)
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.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)
at java.lang.Thread.run(Thread.java:534)

[Julian Kennedy]

All I can tell you is that DBConnection.getDBConnection() returns null. That suggests to me that your configuration is wrong.

Unfortunately I can't help any further as I know nothing about org.dhsinfo.ConnectionPool.DBConnection or how to configure it. I suggest you read the documentation carefully. Try and get a minimal example working first before launching into it.

Jules