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problem while executing user defined method within a servlet

gollusiva kumar
Greenhorn

Joined: Dec 15, 2011
Posts: 2

hi,i have a problem with servlet jdbc programming.I wrote a java class which returns database connection.it's working when we call it from ontother java class,
from a servlet it is showing NullPointerExcception.please tell me reason and suggetion to solve it.

public class LoginPageDataHandlerServlet extends HttpServlet
{
public ServletConfig servletconfig;
public ServletContext context;
public Connection con;
public Statement stmt;

public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
{
doPost(req,resp);
}
public void doPost(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
{
RequestDispatcher dispatcher;
LoginPageDataBean loginData=new LoginPageDataBean();
loginData.setUserName(req.getParameter("UserName"));
loginData.setRegno(req.getParameter("Regno"));
loginData.setUserType(req.getParameter("UserType"));


dispatcher=req.getRequestDispatcher("LoginPageDataValidationServlet");
dispatcher.forward(req,resp);

}
}


LoginPageDataValidationServlet.java


package project.Model;

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

import project.DBA.*;
import project.Operations.*;
import project.Beans.FormBeans.*;

public class LoginPageDataValidationServlet extends HttpServlet
{
RequestDispatcher target;
int regno;
ResultSet rs;
Statement stmt;

public void doPost(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
{




LoginPageDataBean data=(LoginPageDataBean)req.getAttribute("loginData");

String name=data.getUserName();
String Utype=data.getUserType();
String password=data.getRegno();


GeneralOperations validate=new GeneralOperations();


int isMember=validate.Validate(name,password,Utype);


}
}


package project.Operations;

import project.Operations.*;
import project.DBA.*;
import java.sql.*;
import java.util.*;

public class GeneralOperations extends access implements operations
{
/** Method takes three parameters they are username,password and type
of user and validate them .The validation based on excuting a query
if it acquire any result set then it is success if no reuslt ser means it failed and
return some number
*/

String name,password,user;
Connection con;
Statement stmt;
int regno=0;
ResultSet rs;

public void storeDetails(Collection store){}
public void EditDetails(Collections col){}
public Collection showDetails()
{
Collection col=null;
return col;
}


public int Validate(String name,String password,String user)
{
/**

There are Student or College or Administrato name and passwords are the resememble the user identification
upon successfull validation it returns regno of candidate

*/
try
{
stmt=getcreateStatement();
rs=stmt.executeQuery("select regno from "+user+"RegistrationTable where name='"+name+"' and password='"+password+"'");
rs.next();
int regno=rs.getInt(1);
return regno;
}
catch(SQLException e)
{
e.printStackTrace();
return 89;
}
}


}


package project.DBA;
import java.sql.*;
interface connection
{
public Connection getConnection();
}

public class access implements connection
{
public Connection con;
public Statement stmt;
public Connection getConnection()
{
try
{

Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
con=DriverManager.getConnection("jdbcdbc:XE","system","sairam");
System.out.println(con);
}
catch(Exception e)
{
e.printStackTrace();
}
return con;
}
public Statement getcreateStatement()
{
try
{
Connection con=getConnection();
stmt=con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);
}
catch(Exception e)
{
e.printStackTrace();
}
System.out.println(stmt);
return stmt;
}
public Statement getprepareStatemet(String statement)
{
try
{
stmt=getConnection().prepareStatement(statement);
}
catch(Exception e)
{
e.printStackTrace();
}
return stmt;
}
}


error message like below


java.lang.NullPointerException
project.Operations.GeneralOperations.Validate(GeneralOperations.java:42)
project.Model.LoginPageDataValidationServlet.doPost(LoginPageDataValidationServlet.java:34)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
project.Model.LoginPageDataHandlerServlet.doPost(LoginPageDataHandlerServlet.java:36)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)


Validate Method is responsible for acquiring connection and validate the data but i am getting nullpointerexception while executing it only from a servlet ,but it is executing normally in onother java classes
,
Nitin Surana
Ranch Hand

Joined: Jan 21, 2011
Posts: 129

gollusiva kumar wrote:
dispatcher=req.getRequestDispatcher("LoginPageDataValidationServlet");
dispatcher.forward(req,resp);



It should be

Rob Spoor
Sheriff

Joined: Oct 27, 2005
Posts: 19679
    
  18

Gollusiva, can you please UseCodeTags? You can edit your post to add them. Thanks.


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