Question

I have this code:

    public class cuemath extends HttpServlet{
   /**
    *
    */
   private static final long serialVersionUID = 1L;
   String Q;
   String DOWNLOAD="";

   ArrayList<String> _DOWNLOAD_ ;



   public void doGet (HttpServletRequest req,
                   HttpServletResponse res)
   throws ServletException, IOException
   {
     PrintWriter out = res.getWriter();

   try{Connection myCon;


   _DOWNLOAD_ =new ArrayList<String>();



   Statement myStmt;

   String userName = "xxxx";
   String password = "xxxxxxxx";
   String url= "jdbc:mysql://localhost:3306/maths?user="
   +userName
   +"&password="
   +password;

   Class.forName ("com.mysql.jdbc.Driver").newInstance ();



   myCon = DriverManager.getConnection (url);


   myStmt = myCon.createStatement();
   ResultSet rs;

   String pm=req.getParameter("LessonId").trim();
   int p=Integer.parseInt(pm);

   String query="select * from lessons where LESSONS_ID="+p;
   rs= myStmt.executeQuery(query);

   out.println("<CUEMATH>");
   out.println("<lessonid>");


           out.println(rs.getString("LESSONS_ID"));

   out.println("</lessonid>");

   out.println("<lessontext>");

           out.println(replaceTags(rs.getString("LESSONS_TEXT")));

   out.println("</lessontext>");
   out.println("</CUEMATH>");

   }
   catch (Exception e) {
        e.printStackTrace();
}
   }
    private  String replaceTags(String Input){

           if(!Input.equals(null)){

                   String one =">";
                   String two ="<";
                   String five ="\n";
                   String seven ="\\t";

                   String three ="&gt;";
                   String four ="&lt;";
                   String six = "backslash";
                   String eight="tabspace";


                   Input = Input.replaceAll(one, three);
                   Input = Input.replaceAll(two, four);
                   Input = Input.replaceAll(five, six);
                   Input = Input.replaceAll(seven, eight);



                   Input=Input.replaceAll(five, six);
                   Input = Input.replaceAll(one, three);
                   Input = Input.replaceAll(two, four);


                   Input=Input.replaceAll(five, six);
                   return Input;


           }
           else
                   return "";


   }

}

I am getting this error log:

               java.sql.SQLException
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:815)
at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:5528)
at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5448)
at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5488)
at cue.math.cuemath.doGet(cuemath.java:75)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:189)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:91)
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:92)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:325)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:828)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:601)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:619)

I am generating a xml from database values.
I am newbie can anyone help me with this problem?

Answer 1

Before you start retrieving results from the ResultSet object, you should add a call to rs.next()
This call returns a boolean to indicate if a further row is available (in this instance, the first row), and moves the internal result set pointer to the next row of results (in this case the first row).

Often, you will see this in code:

if (rs.next())
{
  // retrieve results from rs object
}

or for multiple rows

while (rs.next())
{
  // each iteration through this loop
  // is a separate result row...
}