Exception coming while connecting to database

[Megha Singhal]

for the following code

import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
import java.lang.String;
import java.sql.Connection;
import java.sql.Statement;
import java.sql.ResultSet;
import javax.naming.*;
import javax.naming.directory.*;
import oracle.jdbc.pool.OracleDataSource;
public class ServletUser extends HttpServlet{

public void init(ServletConfig config) throws ServletException{
super.init(config);
}
/**Process the HTTP Get request*/

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

res.setContentType("text/html");        
PrintWriter out = res.getWriter(); 

Connection con = null;
    Statement st = null;
    ResultSet rs = null;
    

    try {
    
      Context initContext = new InitialContext();                  
      Context envContext = (Context) initContext.lookup("java:/comp/env");                  
      OracleDataSource ds = (OracleDataSource) envContext.lookup("jdbc/abc");                   
      if (envContext == null)throw new Exception("Error: No Context");                
      if (ds == null) throw new Exception("Error: No DataSource");                 
      if (ds != null)                        
      con = ds.getConnection();
   
      st = con.createStatement();
out.println("Connection Pooling Example.<br>");

String id = req.getParameter("P_ID").toString();
String name = req.getParameter("FIRSTNAME").toString();


String sql = "insert into ABC.PERSONS set P_ID='"+name+"',FIRSTNAME='"+name+"'";
int i = st.executeUpdate(sql);
if(i>0){ 
out.println("<br>Record has been inserted"); 
} 
else{ 
out.println("failed to insert the data"); 
} 

					rs.close();
					st.close();
					con.close();

		} catch (SQLException se) {
			out.println("An Error Had occurred while accessing the database");
			out.println("<HR>");

			out.println(se.getMessage());
		}
		
		catch (Exception e) {
			e.printStackTrace();
			out.println("A general Exception has occured!"+e.getMessage());
		} finally {
			try {
				if (rs != null)
					rs.close();
				if (st != null)
					st.close();
				if (con != null)
					con.close();
			} catch (Exception e) {
				out.println(e);
			}
		}
}
}

i 'm getting following ouput
"Connection Pooling Example.
A general Exception has occured!null "

why the above exception is coming?

[Kumaravadivel Subramani]

Could be the problem of extracting the parameters from the request. what printStackTrace() is printed? Try to print "e" as it is when e.getMessage() is null. Debug would be the best option to find the exact problem you encountered.

[Santhosh ayiappan]

Check the stack trace.

Regards
Santhosh

[Amit Ghorpade]

The very first chance of getting the null value is at the following location in your code

String id = req.getParameter("P_ID").toString();

If the request does not contain the parameter P_ID, then the above code will throw a NPE.
Also why are you calling toString() on a string ??
Does not make sense.

[Piyush Mangal]

The following sql seems to be incorrect. Do you want to do update or insert?

String sql = "insert into ABC.PERSONS set P_ID='"+name+"',FIRSTNAME='"+name+"'";