Forum:

so close to having DB data put into bean, then into a table in a JSP

Angel Kal

Greenhorn

Posts: 17

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posted 12 years ago

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Title says it all....I need to place data from a DB into a java bean, and have the information displayed within a table in a jsp.
However I continue to get this error "javax.servlet.ServletException: java.lang.InstantiationException: bean courseBeanList not found within scope".
I am going to paste my code for servlet, jsp, bean, and beanList below. Any help would be greatly appreciated, and I do thank you in advance...
also this is my first post within this forum so be kind please

.
JSP:

<%@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">

<%@page import = "servletPackage.CourseBean"%>
<%@page import = "java.util.*"%>

<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Class Options</title>
    </head>
    <body bgcolor="ccffff">
        <jsp:useBean id="courseBeanList" type="servletPackage.CourseBeanList" scope="session"/>
        
        <h2 align="center">Class Options</h2>

<h4 align="center">Sections Currently Registered For</h4>
        
        <form action=studentServlet.java method=get>
            <table border="1"  >
                <tr>
                    <td >
                        <h6 align=center>Registration Code</h6>
                    </td> 
                    <td >
                        <h6 align=center>Title</h6>
                    </td>
                    <td >
                        <h6 align=center>Term</h6>
                    </td>
                    <td > 
                        <h6 align=center>Instructor</h6>
                    </td>
                    <td >
                        <h6 align=center>Day</h6>
                    </td>
                    <td >
                        <h6 align=center>Time</h6>
                    </td>
                   <td >
                        <h6 align=center>Credits</h6>
                    </td>
                    <td >
                        <h6 align=center>Room</h6>
                    </td> 
                   <td >
                        <h6 align=center>Cost</h6>
                    </td>
                    <td >
                        <h6 align=center>Description</h6>
                    </td>
                    <td >
                        <h6 align=center>Students Enrolled</h6>
                    </td>
               </tr>
            </table> 
               <h4>To unregister from a course, enter a single course ID and click the update Button</h4>
               Course ID: <input type="text" name="unregisterCourseInput">
                          <input type="submit" value="Update" name="unregisterButton">
                          <br></br>
           
           
           <h4 align="center">Schedule of Classes.</h4>
           <table border="1"  >
                <tr>
                    <td >
                        <h6 align=center>Registration Code</h6>
                    </td> 
                    <td >
                        <h6 align=center>Title</h6>
                    </td>
                    <td >
                        <h6 align=center>Term</h6>
                    </td>
                    <td > 
                        <h6 align=center>Instructor</h6>
                    </td>
                    <td >
                        <h6 align=center>Day</h6>
                    </td>
                    <td >
                        <h6 align=center>Time</h6>
                    </td>
                   <td >
                        <h6 align=center>Credits</h6>
                    </td>
                    <td >
                        <h6 align=center>Room</h6>
                    </td> 
                   <td >
                        <h6 align=center>Cost</h6>
                    </td>
                    <td >
                        <h6 align=center>Description</h6>
                    </td>
                    <td >
                        <h6 align=center>Students Enrolled</h6>
                    </td>
               </tr>
               <%
                List cbl = courseBeanList.getCourseBeanList();
                for (int i=0; i < cbl.size(); i++){
                CourseBean cb = (CourseBean) cbl.get(i);
               %>
            <tr>
                <td><%=cb.getRegCode()%></td>
                <td><%=cb.getTitle()%></td>
                <td><%=cb.getTerm()%></td>
                <td><%=cb.getInstructor()%></td>
                <td><%=cb.getDays()%></td>
                <td><%=cb.getTime()%></td>
                <td><%=cb.getCredits()%></td>
                <td><%=cb.getRoom()%></td>
                <td><%=cb.getCost()%></td>
                <td><%=cb.getDescription()%></td>
                <td><%=cb.getNumEnrolled()%></td>
            </tr>
    <%}%>
            </table> 
               <h4>To register for a course, enter a single course ID and click the update Button.</h4>
               Course ID: <input type="text" name="registerCourseInput">
                          <input type="submit" value="Update" name="registerButton">
                          <br></br>
        </form>
    </body>
</html>

Servlet:

package servletPackage;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.sql.*;

/**studentServlet by Angela Kelly
CIS 2454 FA2011 */ 
 
public class studentServlet extends HttpServlet {

private Connection connection;
  private Statement statement;
  private CourseBeanList courseBeanList;

protected void doGet( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException
{
//StudentMenu options
String submit = request.getParameter("sMenuSubmitButton");
 
if (submit.equals("Classes"))
    {
    String url = "/classOptions.jsp";
    RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url);
    dispatcher.forward(request, response);
    
    HttpSession session = request.getSession();
    courseBeanList =(CourseBeanList)session.getAttribute("courseBeanList");
    
    if (courseBeanList == null) 
        {
        courseBeanList = new CourseBeanList();
        session.setAttribute("courseBeanList", courseBeanList);
        }
    try 
        {
         // load driver
         Class.forName("org.apache.derby.jdbc.ClientDriver");
         // connect to database
         connection = DriverManager.getConnection("jdbc:derby://localhost:1527/UniversityDB"); 
         statement = connection.createStatement();
         // obtain list of titles
         ResultSet results = statement.executeQuery("SELECT * FROM classlist" );
         // get row data, create a bean for each row, and
         // add to the list of beans
         int i=0;
            while (results.next()) 
            {
            CourseBean cb = new CourseBean();
            cb.setRegCode(results.getInt(1));
            cb.setTitle(results.getString(2));
            cb.setTerm(results.getString(3));
            cb.setInstructor(results.getString(4));
            cb.setDays(results.getString(5));
            cb.setTime(results.getString(6));
            cb.setCredits(results.getInt(7));
            cb.setRoom(results.getString(8));
            cb.setCost(results.getString(9));
            cb.setDescription(results.getString(10));
            cb.setNumEnrolled(results.getInt(11));
            courseBeanList.setBean( i++, cb );
            }
        }
     catch ( SQLException sqlException ) 
        {
        sqlException.printStackTrace();
        }
     catch ( ClassNotFoundException classException ) 
        {
        classException.printStackTrace();
        }
    }

(there is more after this but doesnt have to do with this process.

Bean class:

package servletPackage;

public class CourseBean
{
int regCode;
String title;
String term;
String instructor;
String days;
String time;
int credits;
String room;
String cost;
String description;
int numEnrolled;

public CourseBean() {}

public CourseBean(int rc, String ttl, String trm, String inst, String dys, String tm, int crds, String rm, String cst, String ds, int ne)
   {
   setRegCode(rc);
   setTitle(ttl);
   setTerm(trm);
   setInstructor(inst);
   setDays(dys);
   setTime(tm);
   setCredits(crds);
   setCost(cst);
   setDescription(ds);
   setNumEnrolled(ne);
   }

//regCode
  public int getRegCode() 
  {
    return(regCode);
  }
  
  public void setRegCode(Integer rc) 
  {
    regCode = rc;
  }
  
  //title
  public String getTitle() 
  {
    return(title);
  }
  
  public void setTitle(String ttl) 
  {
    title = ttl;
  }

//term
  public String getTerm() 
  {
    return(term);
  }
  
  public void setTerm(String trm) 
  {
    term = trm;
  }
  
  //Instructor
  public String getInstructor() 
  {
    return(instructor);
  }
  
  public void setInstructor(String inst) 
  {
    instructor = inst;
  }
  
  //Days
  public String getDays() 
  {
    return(days);
  }
  
  public void setDays(String dys) 
  {
    days = dys;
  } 
  
  //time
  public String getTime() 
  {
    return(time);
  }
  
  public void setTime(String tm) 
  {
    time = tm;
  }  
  
  //Credits
  public Integer getCredits() 
  {
    return(credits);
  }
  
  public void setCredits(int crds) 
  {
    credits = crds;
  }
  
  //room
  public String getRoom() 
  {
    return(room);
  }
  
  public void setRoom(String rm) 
  {
    room = rm;
  }
  
  //cost
  public String getCost() 
  {
    return(cost);
  }
  
  public void setCost(String cst) 
  {
    cost = cst;
  }
  
  //term
  public String getDescription() 
  {
    return(description);
  }
  
  public void setDescription(String ds) 
  {
    description = ds;
  }  
  
  //NumEnrolled
  public Integer getNumEnrolled() 
  {
    return(numEnrolled);
  }
  
  public void setNumEnrolled(int ne) 
  {
    numEnrolled = ne;
  }
}

beanList class:

Stefan Evans

Bartender

Posts: 1845

posted 12 years ago

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The error occurs because you are visiting the page with the bean in it before it has been put into scope.
Is that a valid transition?

The difference is in your useBean statement. You have:

To get rid of the error message you can change it to:

The difference between using "class" and "type" is that with "class", if the bean doesn't already exist, it will instantiate it. Specifying type means that the bean should already be present, and it will throw an error if it is not.

As far as I can tell the bean is being instantiated and set into session in your servlet, so making sure you visit the servlet's url before you visit the JSP will also work around this issue, and may be the correct solution. It depends on your intended workflow.

Other feedback:
Rather than using scriptlet code in a JSP, it is suggested to use JSTL and EL.

Your Course bean seems a very thin wrapper around a List. I might almost suggest putting a list in scope rather than using a course bean.

In terms of Database code, it could be improved by using JNDI data source declared in your server, which would allow the server to do connection pooling, as opposed to opening a new database connection on each invocation of the servlet.
But what you have works :-)

Angel Kal

Greenhorn

Posts: 17

I like...

posted 12 years ago

Number of slices to send:

Optional 'thank-you' note:

Send

Thanks for your help, that did the trick

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