NullPointerException

NullPointerException

I wonder why this coding could not work since i really need to pass the selected choice inside, giving me real time data change from the database.I guess this is the structure I need to to so.The jsp just couldn't read from the parameter "name" but if i directly insert a string into the varaible answer, it will work. Is there anything can be done to fix this? It is from the 'Passing Parameter' topic.

test.jsp

<%@ page language="java" import="java.util.*"%>
<%@ page import="java.sql.*,java.io.*,javax.servlet.*,javax.servlet.http.*,java.lang.String
"%>
<html>
<head>
<script type="text/javascript">
function change()
{
var answer = document.getElementById('selc').value;
window.location.replace("test.jsp?name="+answer);

<%

String connectionURL = "jdbc:mysql://localhost:3306/test";
Connection connection=null;
ResultSet rs;
response.setContentType("text/html");
String price = "0";
String answer = request.getParameter("name");

try {
// Load the database driver
Class.forName("com.mysql.jdbc.Driver");
// Get a Connection to the database
connection = DriverManager.getConnection(connectionURL, "root", "123");
//Select the data from the database
String sql = "select * from message where message = '"+answer+"'";
Statement s = connection.createStatement();
s.executeQuery (sql);
rs = s.getResultSet();

while (rs.next ()){

price = rs.getString("price");
}

rs.close ();
s.close ();
}


catch(Exception e)
{
System.out.println("Exception is ;"+e);
}

%>
document.getElementById('textvalue').value= <%= price %>;
}
</script>
</head>
<body>
<h1>Use of Select Box in JSP</h1>
<table border="1" width="41%" height="53" cellspacing="0" cellpadding="3"
bgcolor="#000080" bordercolorlight="#FFFFFF">
<tr>
<td width="100%" height="18" colspan="2"><b>
<font color="#FF00FF">Select items from select box</font></b></td>
</tr>
<tr>
<td width="17%" height="23">
<select name="ActionSelect" onChange="change()" id="selc" >
<%Iterator itr;%>
<% List data= (List)request.getAttribute("data");
for (itr=data.iterator(); itr.hasNext(); )
{
String value=(String)itr.next();
%>
<option value=<%=value%>><%=value%></option>
<%}%>
</select>
</td>
<td width="83%" height="23"><input type="text" id="textvalue" />
</td>
</tr>
</table>
</body>
</html>
_________________________________________________________________________

DataServlet.java

package Servlet;

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

public class DataServlet extends HttpServlet{

private ServletConfig config;
//Setting JSP page
String page="test.jsp";

public void init(ServletConfig config)
throws ServletException{
this.config=config;
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

PrintWriter out = response.getWriter();
//Establish connection to MySQL database
String connectionURL = "jdbc:mysql://localhost:3306/test";
Connection connection=null;
ResultSet rs;
response.setContentType("text/html");


List dataList=new ArrayList();


try {
// Load the database driver
Class.forName("com.mysql.jdbc.Driver");
// Get a Connection to the database
connection = DriverManager.getConnection(connectionURL, "root", "123");
//Select the data from the database
String sql = "select message from message";
Statement s = connection.createStatement();
s.executeQuery (sql);
rs = s.getResultSet();
while (rs.next ()){
//Add records into data list
dataList.add(rs.getString("message"));
}
rs.close ();
s.close ();
}


catch(Exception e)
{
System.out.println("Exception is ;"+e);
}

request.setAttribute("data",dataList);


//Disptching request
RequestDispatcher dispatcher = request.getRequestDispatcher(page);
if (dispatcher != null){
dispatcher.forward(request, response);
}
}
}
___________________________________

message db

id message price
5 amit 5
1 amir 6
2 raghuwanshi 12
3 raghuw 100
4 suman 149.99
6 calamity 99.99
7 muthusamy 99.99
View Answers

April 20, 2010 at 5:02 PM

Hi Friend,

We have made changes in jsp file 'test.jsp'and there is no need to use DataServlet.Here, we have taken our database table fields.

test.jsp:

<%@ page language="java" import="java.util.*"%>
<%@ page import="java.sql.*,java.io.*,javax.servlet.*,javax.servlet.http.*,java.lang.String
"%>
<html>
<head>
<script type="text/javascript">
function change()
{
var answer = document.getElementById('selc').value;
window.location.replace("test.jsp?name="+answer);
}
</script>
</head>
<%
String connectionURL = "jdbc:mysql://localhost:3306/register";;
Class.forName("com.mysql.jdbc.Driver");
Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test";, "root", "root");
String ans=request.getParameter("name");
response.setContentType("text/html");
String address = "";
String name = "";
try {
String sql = "select * from data where name = '"+ans+"'";
Statement s = connection.createStatement();
s.executeQuery (sql);
ResultSet rs = s.getResultSet();
while (rs.next ()){
address = rs.getString("address");
name=rs.getString("name");
}
rs.close ();
s.close ();
}
catch(Exception e){
System.out.println("Exception is ;"+e);
}
System.out.println(address);

%>

<body>
<h1>Use of Select Box in JSP</h1>
<table border="1" width="41%" height="53" cellspacing="0" cellpadding="3"
bgcolor="#000080" bordercolorlight="#FFFFFF">
<tr>
<td width="100%" height="18" colspan="2"><b>
<font color="#FF00FF">Select items from select box</font></b></td>
</tr>
<tr>
<td width="17%" height="23">
<select onChange="change();" id="selc" >
<%
Statement st=connection.createStatement();
ResultSet rs=st.executeQuery("select name from data");
while(rs.next()){
%>
<option value="<%=rs.getString("name")%>"><%=rs.getString("name")%></option>
<%
if(name.equals(rs.getString("name"))){
%>
<option value="<%=rs.getString("name")%>"selected=selected><%=rs.getString("name")%>></option>
<%
}

}%>
</select>
</td>
<td width="83%" height="23"><input type="text" id="textvalue" value="<%= address %>" />
</td>
</tr>
</table>
</body>
</html>

Thanks









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