problem in inserting data in msaccess

[kiranme]

<%@ page language = "java" import = "java.sql.*" %>
<%@ page import = "java.sql.*" %>
<%@ page import = "java.text.*" %>
<%
String username,passw,passw1,compnam,tinn;
username= request.getParameter("username");
passw = request.getParameter("pwd");
passw1 = request.getParameter("pwd1");
compnam = request.getParameter("compname");
tinn=request.getParameter("TIN");

Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
String st = "jdbc:odbc:loginval";
Connection cn = DriverManager.getConnection(st," "," ");
Statement stmt = cn.createStatement();
String sql = "insert into register " ;
sql +="(username,pwd,pwd1,compname,TIN)";
sql += " values ('";
sql += username ;
sql += "','";
sql += passw;
sql += "','";
sql += passw1;
sql += "','" ;
sql += compnam ;
sql += "','" ;
sql += tinn;
sql += "')";
int val = stmt.executeUpdate(sql);
cn.close();
if(val==1)
{
%>
<jsp:forward page = "success.html"/>
<%
}
%>
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this is my code, i am not able to insert any values in to my table thru this code, when i submit for the first time null values are stored in the table i mean "null" is getting displayed in the table.
when i submit for the second time then the server throws an error "general error"
some one help me plz
thanks in advance

[jwenting]

YUGH!!!!!!

You don't properly close your database resource, you use String concatenation all over the place, you have massive scriptlets in a JSP, you place business logic in a JSP, you don't use code tags.

And you don't seem to understand what you're doing.

Of course it stores all null values when you call the page as those request parameters won't have been set.
And most likely the error on subsequent calls is a primary key violation from trying to insert another null value (I guess you declared username to be unique).