The following sample program got empty display , why?

Question

import pool.ConnectionPool;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;
import javax.sql.*;
public class Update extends HttpServlet {   
    Statement stmt = null;
    ResultSet rs = null;
    Connection conn = null;
ConnectionPool connectionPool = null;
* Creates a connection pool.
public void init() throws ServletException
String jdbcDriver = "com.microsoft.jdbc.sqlserver.SQLServerDriver";
String dbURL ="jdbc:microsoft:sqlserver://localhost:1433; DatabaseName=pubs";
try
//instantiate the connection pool object by passing the
//jdbc driver, database URL, username, and password
connectionPool = new ConnectionPool(jdbcDriver, dbURL,
"test","1234");
//specify the initial number of connections to establish
connectionPool.setInitialConnections(5);
//specify number of incremental connections to create if
//pool is exhausted of available connections
connectionPool.setIncrementalConnections(5);
//specify absolute maximum number of connections to create
connectionPool.setMaxConnections(20);
connectionPool.createPool(); //create the connection pool
catch(Exception e)
System.out.println("Error: " + e);
/** Destroys the servlet.
    public void destroy() {
    public void doGet(
    HttpServletRequest request,
    HttpServletResponse response)
    throws IOException, ServletException {  
       }// end of DoGet
  public void doPost(HttpServletRequest req, HttpServletResponse res)
    throws ServletException, IOException {
     res.setContentType("text/html");
    PrintWriter out = res.getWriter();
    PreparedStatement ps = null;
      try{
            String myName= req.getParameter("uname");             
             String password =req.getParameter("oldpassword");
             String Npassword =req.getParameter("pas1");          
            String ErrMsg = "";
              //get free connection from pool
         conn =connectionPool.getConnection();
             stmt = conn.createStatement(
                       ResultSet.TYPE_SCROLL_SENSITIVE,
                       ResultSet.CONCUR_READ_ONLY);
         rs = stmt.executeQuery("select * FROM users where Name='"+myName+"' and password='"+password+"'" );
              int count =0;//how many rows we can find.
              while (rs.next()){
                  count++;
           if(count<1){
                     ErrMsg ="UserName and Password are not there, can't update !";
                    HttpSession userSession = req.getSession(true);           
                    userSession.setAttribute("ErrMsg", ErrMsg);
                      RequestDispatcher disp;
                    disp = getServletContext().getRequestDispatcher("/secure/UpdateError.jsp");
                    req.setAttribute("ErrMsg",ErrMsg);
                   disp.forward(req, res);
         else{
            conn.setAutoCommit(false);
                   Statement stmt = conn.createStatement();
             String sql ="UPDATE users SET password='"+Npassword+"' where Name='"+myName+"'and password='"+password+"'";
                     ps = conn.prepareStatement(sql);            
                      ps.executeUpdate();                    
           conn.commit();
           conn.setAutoCommit(true);
         //get current session, create if it doesn't exits
           HttpSession userSession = req.getSession(true);
           userSession.setAttribute("Name", myName);
           userSession.setAttribute("Password", Npassword);
       RequestDispatcher disp;
       disp = getServletContext().getRequestDispatcher("/secure/update.jsp");
       req.setAttribute("Name", myName);
       req.setAttribute("password", Npassword);
       disp.forward(req, res);
      }// end else
    }//end try
   catch(SQLException e) {
     finally {
      try {
        if(rs != null)
          rs.close();
          rs = null;
        if(stmt != null)
          stmt.close();
          stmt = null;
        if(conn != null)
          conn.close();
          conn = null;
      } //end try
    catch (SQLException e) {}   
  }//end finally
} // end doPost
public String getServletInfo()
    return "A Simple Servlet";
}// end of ContrUpdate
       jsp
<%@ page buffer="16kb"%>
<html>
<head>
<title>NewMember</title>
<body >
<center>
<h3> Welcome Back,<%= request.getAttribute("Name")%></h3>
<h3> you are new information on our Login table are... you can use these userName and Password to login</h3>
<table width="63%" border="1" align="center" >
<tr>
<th  bgcolor="#ffffcc" width="26%">UserName: </th>
<td><%= request.getAttribute("Name") %></td>
</tr>    
<tr>
  <th bgcolor=#ffffcc width="26%">Password: </th>
   <td><%= request.getAttribute("password") %> </td>
</tr>
</table>
</center>
</body>
</html>

Answer 1

There are a lot of try and forget blocks.
catch (SQLException e) {}   
  }within your code.
You should at least log the Exception, better would be to rethrow the Exception and display an ErrorPage.
You may not close the connection within the finally block
if(rs != null)
          // when a Exception occurs here neither the statement nor the
         // connection will be closed.
          rs.close();
          rs = null;
        if(stmt != null)
          stmt.close();
          stmt = null;
        if(conn != null)
          conn.close();
          conn = null;
        }If the creation of the Connection Pool fails your doPost Method will throw a NullPointerException becauseconnectionPool is null.
Your init Method should throw an Exception in this case.
You use a PreparedStatement but you don't use Parameters
   String sql ="UPDATE users SET password='"+Npassword+"' where     Name='"+myName+"'and password='"+password+"'";
                     ps = conn.prepareStatement(sql);            
                      ps.executeUpdate();                 
// should be
   final String sql ="UPDATE users SET password=? where Name=? and password=?";            
                     ps = conn.prepareStatement(sql);            
                     ps.setSring(1, Npassword);
                     ps.setString(2,myName);
                     ps.setString(3, password);
                      ps.executeUpdate();