Logon verification servlet

Question

Hi!
I have a servlet that verifies a user logon to a website using a MySQL database and Tomcat 5.5. Unfortunately, I get the following error:
java.lang.IllegalStateException
     org.apache.catalina.connector.ResponseFacade.sendRedirect(ResponseFacade.java:423)
     Autobar.checkUser.service(checkUser.java:102)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
     org.apache.catalina.servlets.InvokerServlet.serveRequest(InvokerServlet.java:419)
     org.apache.catalina.servlets.InvokerServlet.doPost(InvokerServlet.java:169)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
It seems like it connects to the database, but I think I'm having problems with the redirects. Here's the code:
package Autobar;
import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class checkUser extends HttpServlet
private PrintWriter out = null;
private String userid      = "";
private String password     = "";
private String companyId= null;
private String companyName= null;
private String shipFromId=null;
private PreparedStatement pstmt,pstmt1,st = null;
private Connection con = null;
public synchronized void service(HttpServletRequest req, HttpServletResponse res) throws
                    ServletException, IOException
     res.setContentType("text/html");
     out = res.getWriter();
     HttpSession userSession = req.getSession(true);
     userid = req.getParameter("txtUserID");
     password = req.getParameter("txtPassword");
     if(userid != null)
     userid      = userid.toUpperCase().trim();
     if(password != null)
     password = password.toUpperCase().trim();
     else
     out.println("<B><H3>USERNAME AND PASSWORD should NOT NULL </H3></B>");
     out.println(userid);
     out.println(password);
     dbConnection dbc = new dbConnection();     
     try{
          con = dbc.makeConn();
          if(con != null)
          pstmt = con.prepareStatement("select * from User where userid=? and password=?");          
          pstmt1 = con.prepareStatement("select CompanyName from Company where CompanyID=?");
          else
          out.println("connection is null");
     if((userid != null) && (password != null))
     pstmt.setString(1,userid);
     pstmt.setString(2,password);
     else
     out.println("please fill the userid and password ..");
     ResultSet rs = pstmt.executeQuery();          
     if(rs.next())
     companyId = rs.getString("CompanyID");
     shipFromId= rs.getString("CompanyShipID");                    
     userSession.putValue("companyId",companyId);
     userSession.putValue("userId",userid);
     pstmt1.setString(1,companyId);
     ResultSet rs1 = pstmt1.executeQuery();
     if(rs1.next())
          companyName = rs1.getString("CompanyName");
     userSession.putValue("companyName",companyName);          
     if(shipFromId != null)
          st = con.prepareStatement("select CompanyShipName from companyshipfrom where CompanyID=? and CompanyShipID=?");
          st.setString(1,companyId);
          st.setString(2,shipFromId);
          ResultSet r1 = st.executeQuery();
          if(r1.next())
               userSession.putValue("shipFromName",r1.getString("CompanyShipName"));
          userSession.putValue("shipFromId",shipFromId);     
          else
          res.sendRedirect("../servlet/Autobar.selectShipFrom");
     res.sendRedirect("../servlet/Autobar.getShippers?companyid="+companyId);
     else
     //out.println("<br>");
     //out.println("<B> No company matches with your entry...");
          res.sendRedirect("../Error.jsp?errorCode="+ 1);
     catch(SQLException se){out.println("Exception at..."+se.getMessage()); }
public void destroy()
     super.destroy();
     if(con != null)
          try{
          con.close();
          }catch(SQLException se){}
Any assistance would be greatly appreciated!
Sincerely,
Adam

Answer 1

Once you print something out the response stream, you can no longer redirect it, it is committed. That is the IllegalStateException you are seeing.
You should modify your code not to print anything to the response stream if you need to redirect.