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JDBC and Relational Databases

After UPDATE Statement, Null Value is fetched

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posted 14 years ago

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I made this code which simply fetches the data and each row has a Edit link Besides it...
When i click on Edit, the record appears perfectly, but when i make changes and click on save, it refreshes and shows null values in every Text Box. However, It makes changes to the Table.

This is the Code For EDIT page

#  /* 
#  * To change this template, choose Tools | Templates 
#  * and open the template in the editor. 
#  */  
#   
# import java.sql.*;  
# import java.io.*;  
# import javax.servlet.*;  
# import javax.servlet.http.*;  
#   
# /** 
#  * 
#  * @author Ezrockgw 
#  */  
# public class edit extends HttpServlet {  
#     static String s;  
#    Connection con;  
#    PreparedStatement ps;  
#     /**  
#      * Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods. 
#      * @param request servlet request 
#      * @param response servlet response 
#      * @throws ServletException if a servlet-specific error occurs 
#      * @throws IOException if an I/O error occurs 
#      */  
#     protected void processRequest(HttpServletRequest request, HttpServletResponse response)  
#     throws ServletException, IOException {  
#         response.setContentType("text/html;charset=UTF-8");  
#         PrintWriter out = response.getWriter();  
#         try {  
#   
#                   Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");  
#   
#   
#                 //Connect to  Data source  
#                  con = DriverManager.getConnection("jdbc:odbc:gdsn", "", "");  
#   
#   
#                  Statement theStatement=con.createStatement();  
#                   s = request.getParameter("value");  
#                 ResultSet theResult=theStatement.executeQuery("select * from Qtable where Number="+s);  
#                 theResult.next();  
#                 String q2 = theResult.getString(2);  
#                 String q3 = theResult.getString(3);  
#                 String q4 = theResult.getString(4);  
#                 String q5 = theResult.getString(5);  
#                 String q6 = theResult.getString(6);  
#                 String q7 = theResult.getString(7);  
#   
#   
#   
#             out.println("<html>");  
#             out.println("<head>");  
#             out.println("<title>edit</title>");    
#             out.println("</head>");  
#             out.println("<body>");  
#             out.println("<form name=\"abc\" action =\"edit\">");  
#             out.println("<h2> Question : </h2>");  
#             out.println("<input type=\"text\"  size=\"45\" name=\"question\" value=\"" +q2+ "\">");  
#             out.println(" <br><br><br> <b>Option 1</b>  <input type=\"text\" name=\"op1\" value=\"" +q3+ "\"> <br><br>");  
#             out.println("<b>Option 2</b> <input type=\"text\" name=\"op2\" value=\"" +q4+ "\"> <br><br>");  
#             out.println(" <b>Option 3</b> <input type=\"text\" name=\"op3\" value=\"" +q5+ "\"> <br><br>");  
#             out.println("<b>Option 4</b> <input type=\"text\" name=\"op4\" value=\"" +q6+ "\"> <br><br>");  
#             out.println("<b>Answer </b> <input type=\"text\" name=\"ans\" value=\"" +q7+ "\"> <br><br>");  
#             out.println("<input type=\"hidden\" name=\"value\" value=\"" +s+ "\"> <br><br>");  
#             out.println("<input type=\"submit\" name=\"Make Changes\" >  <input type=\"reset\" name=\"Reset\">");  
#              out.println("</body>");  
#             out.println("</html>");  
#   
#             if ((!q2.equals(request.getParameter("question"))) || !q3.equals(request.getParameter("op1") )|| !q4.equals(request.getParameter("op2") ) || !q5.equals(request.getParameter("op3") ) || !q6.equals(request.getParameter("op4") ) || !q7.equals(request.getParameter("ans") ) )  
#             {  
#             ps = con.prepareStatement("UPDATE Qtable SET Question = \'"+ request.getParameter("question") +"\',opt1 = \'"+ request.getParameter("op1") +"\',opt2=\'"+ request.getParameter("op2")  +"\',opt3 =\'"+ request.getParameter("op3")  +"\',opt4 =\'"+ request.getParameter("op4")  +"\',ans =\'"+ request.getParameter("ans")  +"\' WHERE Number="+s);  
#             int m = ps.executeUpdate();  
#             }  
#   
#         }  
#   
#         catch (ClassNotFoundException e)  
#             {  
#                 e.printStackTrace();  
#   
#             }  
#   
#             catch(SQLException e)  
#             {  
#                 e.printStackTrace();  
#             }  
#          catch(Exception e)  
#             {  
#                 e.printStackTrace();  
#             }  
#   
#   
#         finally {  
#             out.close();  
#         }  
#     }   
#   
#     // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">  
#     /**  
#      * Handles the HTTP <code>GET</code> method. 
#      * @param request servlet request 
#      * @param response servlet response 
#      * @throws ServletException if a servlet-specific error occurs 
#      * @throws IOException if an I/O error occurs 
#      */  
#     @Override  
#     protected void doGet(HttpServletRequest request, HttpServletResponse response)  
#     throws ServletException, IOException {  
#         processRequest(request, response);  
#     }   
#   
#     /**  
#      * Handles the HTTP <code>POST</code> method. 
#      * @param request servlet request 
#      * @param response servlet response 
#      * @throws ServletException if a servlet-specific error occurs 
#      * @throws IOException if an I/O error occurs 
#      */  
#     @Override  
#     protected void doPost(HttpServletRequest request, HttpServletResponse response)  
#     throws ServletException, IOException {  
#         processRequest(request, response);  
#     }  
#   
#     /**  
#      * Returns a short description of the servlet. 
#      * @return a String containing servlet description 
#      */  
#     @Override  
#     public String getServletInfo() {  
#         return "Short description";  
#     }// </editor-fold>  
#   
# }  
#

Prabhakar Reddy Bokka

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posted 14 years ago

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OK.

make a commit of first transaction before you fetch with the second statement.

con.commit();

SCJP 5, SCWCD 5

Gaurav Wadhwani

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posted 14 years ago

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thank you sir but that wont Solve the problem. This problem is combination of Java and SQL.

Initially i thought, it was Servlet only problem, then it became purely SQL problem, and then a Combination.

The complete solution is here

https://coderanch.com/t/510993/Servlets/java/Servlet-Displays-Old-DB-Entries

Jan Cumps

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posted 14 years ago

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Can you check the value of s during the refresh?

OCUP UML fundamental and ITIL foundation

Gaurav Wadhwani

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posted 14 years ago

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value of s remains same. When on Display List page, i click on edit and it attaches a parameter "value" which becomes the value of s. Then later on it stays in the servlet as hidden field and keeps passing no matter how many times i refresh it.

Jan Cumps

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posted 14 years ago

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Solved in https://coderanch.com/t/510993/Servlets/java/Servlet-Displays-Old-DB-Entries

OCUP UML fundamental and ITIL foundation

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