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Storing resultset into arraylist

Bhardwaj Shweta

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posted 13 years ago

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hello

I need to store my result set into an ArrayList and then to display data in a jsp page..

//coding in servlet

//coding is jsp page

but its not showing anything,may be its taking long time to process it..please help

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Shweta Bhardwaj

Mohamed Sanaulla

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posted 13 years ago

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You must be getting ClassCastException. If you carefully observe in the servlet you have an ArrayList of ArrayList but in the jsp you are trying to access the list as just a list of Strings and that might be the reason why you are seeing no output. Alternatively you can have one class for your Resultset data- say MyClass and each of the attributes are the columns from the resultset. And then you can have an arraylist declared as ArrayList<MyClass>.

Also try to remove the Java code dangling withing the JSP- You might want to make use of JSP tag library for traversing through the lists.

Mohamed Sanaulla | My Blog | Author of Java 9 Cookbook | Java 11 Cookbook

Bhardwaj Shweta

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hello Mohamed

can i typecast it into Arraylist!!!

as far as separate class for result set,i am new to java and quite apprehensive regarding making so many classes ,i think i will get confuse :P i know you are telling me the correct approach but can i fix this problem and then make my code better by making separate classes.

and can you give me some example how to use tag library for traversing through the lists.

Thank you so much

Regards,
Shweta Bhardwaj

Mohamed Sanaulla

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You have to typecast it to ArrayList and then traverse. You can add an instanceof check before typecasting and if the instanceof fails then you can tell the user that there was some issue in retreiving the data. It will not affect if you have too many classes. It will only help you modularize your application.

For JSTL you can visit this: http://jstl.java.net/ Its basically set of JSP tags which you can use instead of these Java code.

Mohamed Sanaulla | My Blog | Author of Java 9 Cookbook | Java 11 Cookbook

utsav gupta

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posted 13 years ago

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Hi

What i would suggest is to remove the ArrayList 'list' and simply pass a1 on to the Jsp. Hence in the Jsp you just have to change the 'list' to 'a1' and access all the elements straightway from it.

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utsav.

Bhardwaj Shweta

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here is my complete code:
//jsp page

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
   "http://www.w3.org/TR/html4/loose.dtd">

<html>
    <head>
         <%@ page import = "java.sql.*" %>
        <%@ page import = "java.util.*" %>
       <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
        <link href=".\css1.css" rel="stylesheet" type="text/css" />
        
        <title>Projects Information</title>

</head>
 <body  style ="background:url(images/wall.JPG) repeat-x #F6F4E4;">
     <h2>PR Tracker </h2>
     <div id="form">
          <form  name="projectform" method="post" action="operationservlet" >
              <table  >
                  <%
ArrayList arr = (ArrayList) session.getAttribute("list");
String myString ="";
if(arr.isEmpty()==false)
{
for(int i = 0; i < arr.size(); i++)
{
myString = (String)arr.get(i);
}
}
else
{
System.out.println("Array is empty");
}
%> 
<tr>

<td>
project Name
</td>
<td>
    <input type="text" name="pname" id="pname" size="25" value="<%=myString%>" disabled>
</td>

</tr>
<tr>
<td>
Description/Remarks
</td>
<td><input type="text" name="remarks" size="25" value="<%=myString%>"  disabled>
</td>
</tr>
<tr>

<td>
Client IT Contact Person
</td>
<td><input type="text" name="contact" size="25" value="<%=myString%>" disabled>
</td>

</tr>
<tr>

<td>
Business Sponsor
</td>
<td><input type="text" name="sponsor" size="25" value="<%=myString%>" disabled>
</td>
</tr>
<tr>

<td>
Business Project owner
</td>
<td><input type="text" name="owner" size="25" value="<%=myString%>" disabled>
</td>
</tr>
<tr><td>Priority</td>
<td>
<Select name="priority" disabled>
<option selected><%=myString%></option>
<option>High</option>
<option>Medium</option>
<option>Low</option>
</Select></td>
</tr>
</table>

<table  class="navigationclass"  >
<tr><td > </td></tr>
<tr><td  >Operations</td><td  >Navigation</td></tr>
<tr>
<td><input type="submit"  name="option" value="save"  disabled></td>
<td><input type="submit"  name="option" value="add" ></td>
<td><input type="submit"  name="option" value="delete" ></td>
<td><input type="submit"  name="option" value="cancel"  disabled></td>
<td><input type="submit"  name="option" value="edit" ></td>
<td><input type="submit"  name="option" value="first" ></td>
<td><input type="submit"  name="option" value="prev" ></td>
<td><input type="submit"  name="option" value= "next" ></td>
<td><input type="submit"  name="option" value="last" ></td>
<td><input type="submit"  name="option" value="find" ></td>
</tr>
</table>
          </form>
         
     </div>
        
    </body>
</html>

// servlet

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 *
 * @author Core 2Duo
 */
public class projectservlet extends HttpServlet {

/**
     * 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();
          HttpSession session = request.getSession(true);

Connection con=null;
        Statement st;
        ResultSet rs;
        ArrayList al = new ArrayList();
        ArrayList list = new ArrayList();
        try {
            Class.forName("com.mysql.jdbc.Driver");
            con=DriverManager.getConnection("jdbc:mysql://localhost:3306/pr","root","123");
        }
        catch(Exception e)
        {
            out.println(e.getMessage());

}
        try{
            st=con.createStatement();
            rs=st.executeQuery("select * from pr_project");

out.println("<html>");
            out.println("<head>");
            out.println("<title>Servlet servlet1</title>");
            out.println("</head>");
            out.println("<body>");

//    response.sendRedirect("first.jsp");

if(rs.next())
            {
                 al.add(rs.getString("pname"));
	         al.add(rs.getString("remarks"));
                 al.add(rs.getString("cnt"));
                 al.add(rs.getString("bsponsor"));
	         al.add(rs.getString("bprowner"));
                 al.add(rs.getString("priority"));
                 list.add(al);
                 session.setAttribute("list",list);
                RequestDispatcher rd=getServletContext().getRequestDispatcher("/project.jsp");
                rd.forward(request,response);

}
            else
            {

RequestDispatcher rd=getServletContext().getRequestDispatcher("/errorpage.jsp");
                rd.forward(request, response);

}
            out.println("</body>");
            out.println("</html>");

}catch(SQLException e1)
        {
            out.println(e1.getMessage());
        }
        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>

}

i tried to typecast it but its still not showing any result..

can you please modify the code
Thank you

Regards,
Shweta Bhardwaj

Vijitha Kumara

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posted 13 years ago

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Why use two ArrayList instances here?
Try with one array list instance, then you may populate the list as you need. Also move your request dispatcher code out of the result set access code.

And you better off populating the appropriate object with the data and add it to the array list then retrieve them in the JSP. As already noted move all the Java code from the JSP instead use the JSTL, EL , standard.custom actions for data manipulations in JSP.

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Bhardwaj Shweta

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posted 13 years ago

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@vijitha

I have changed my code to

and servlet is working fine:)
but in my jsp page its showing value of String s6 = rs.getString("priority") in all the fields..
error is in my logic
// jsp

when the control gets out of the loop mystring holds value of s6. how to fix it

Regards,
Shweta Bhardwaj

Bhardwaj Shweta

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posted 13 years ago

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in between i am learning how to use JSTL and EL.

Regards,
Shweta Bhardwaj

Bhardwaj Shweta

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posted 13 years ago

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In order to use JSTL
i have added <%@taglib prefix="c" uri="http://java.sun.com/jstl/core"%>

but its showing and error:
"The absolute uri:http://java.sun/jstl/core cannot be resolved in either web.xml or the jar files deployed with application"
i have already added two jar files
jstl-impl-1.2.jar and jstl-api-1.2.jar

how to resolve it please help

Regards,
Shweta Bhardwaj

Mohamed Sanaulla

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posted 13 years ago

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I would suggest you to start a new thread for any new query so that others can also have a look at the query.

Mohamed Sanaulla | My Blog | Author of Java 9 Cookbook | Java 11 Cookbook

Mohamed Sanaulla

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posted 13 years ago

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Bhardwaj Shweta wrote:
and servlet is working fine:)
but in my jsp page its showing value of String s6 = rs.getString("priority") in all the fields..
error is in my logic

You are using the same variable for all the values in the list and consequently the variable will end up having the value of the last field. So you need not use a variable instead just do an get on the list.

Mohamed Sanaulla | My Blog | Author of Java 9 Cookbook | Java 11 Cookbook

Bhardwaj Shweta

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@ Mohamed
Thanks for replying:)
umm can you please give some example.

if i have <input type="text" name="pname" id="pname" size="25" value="<%=##%>" disabled>
<input type="text" name="remarks" size="25" value="<%=##%>" disabled>
how should i retrieve respective value from list object??

Regards,
Shweta Bhardwaj

Vijitha Kumara

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posted 13 years ago

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As I said encapsulate all the fields for a given record in an object (add it to the list) and access that object in the JSP. This way you can have many records retrieved easily in the JSP. But with this code, retrieve the data to different variables(since this is only for one record you are using) for each field and use them in the HTML elements.

Since you are learning the JSTL etc... you can re-factor the code to use them once you get this to work.

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Mohamed Sanaulla

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posted 13 years ago

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With the current implementation- You can declare different variables like mystring for each column in the resultSet and then use them alongside the html code. I cant think of other way with the current implementation. The one i suggested using the list.get might not work

Mohamed Sanaulla | My Blog | Author of Java 9 Cookbook | Java 11 Cookbook

Mohamed Sanaulla

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posted 13 years ago

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Vijitha Kumara wrote:As I said encapsulate all the fields for a given record in an object (add it to the list) and access that object in the JSP. This way you can have many records retrieved easily in the JSP. But with this code, retrieve the data to different variables(since this is only for one record you are using) for each field and use them in the HTML elements.

This is a better approach and the code thus written is more readable. And I remember suggesting this.

Mohamed Sanaulla | My Blog | Author of Java 9 Cookbook | Java 11 Cookbook

Bhardwaj Shweta

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posted 13 years ago

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Thank you guys for helping me out, i will try this

Regards,
Shweta Bhardwaj