Validation of data

Can anyone help me with simple authentication in the existing code.

In this i need to check if the input data exist in the particular field in database, if it does not exist then insert into database else throw an error

import javax.servlet.http.HttpServlet;

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

public class subServlet extends HttpServlet{
  public void doGet(HttpServletRequest req,
                    HttpServletResponse res)
                      throws ServletException, IOException{
   System.out.println("req fetched");                    
    try {
      Statement stmt;//used for database access
      ResultSet rs;//used for database access

      //Set the content type of the data to be sent back
      // to the client.
      //Get an output writer object to send data back to
      // the client.
      PrintWriter out = res.getWriter();
      //Register the JDBC driver
      String JDBCDriver="oracle.jdbc.driver.OracleDriver";
      //Construct URL for database on node3
      String JDBCUrl = "jdbc:oracle:dev";
      String JDBCUser = "bang";
      String JDBCPassword = "viz";

      //Get a connection to the database
       Connection con = DriverManager.getConnection(JDBCUrl, JDBCUser, JDBCPassword);                  

      //Get a Statement object
      stmt = con.createStatement();

      //Get the two incoming data parameters from the
      // client
       String email_id = req.getParameter("email_id");
       System.out.println("EmailID :"  + email_id);
      //Put the data into the database table. Don't forget
      // to enclose the string data in single quotes to
      // satisfy the SQL syntax requirement.
     * Add the value into database if true only.
     * @return true, if add was successful

     if(req.getParameter("email_id") == (){
             System.out.println("Sorry Dude");
             stmt.executeUpdate("INSERT INTO SUB_TABLE (email_id) values ('" + email_id + "')");                    
            System.out.println("insert SUB_TABLE");

       stmt.executeUpdate("INSERT INTO SUB_TABLE (email_id) values ('" + email_id + "')");                    
       System.out.println("insert SUB_TABLE");
      //Use the statement object to execute a query on the
      // database.
      rs = stmt.executeQuery("SELECT * from SUB_TABLE  ORDER BY EMAIL_ID");
      //Extract data from the ResultSet object and display
      // in the HTML page sent back to the client.
         System.out.println("Display all results:");
          while( {
          String e = rs.getString("EMAIL_ID");
         String a = rs.getString("ACT_ID");
         System.out.println(e + "   " + a);
    }//end while loop
      //Close the connection to the database      
    }catch( Exception e ) {
    }//end catch
  }//end doGet()
}//end class
Who is Participating?
NushiConnect With a Mentor Commented:
its not clear to me what you are trying to do.
you want to check if you already have a record in the database for acertain field?

the way to avoid it is to decleare the fiels as PRIMARY key (in the database) and by doing that you can insert each value only once and you will get exception when trying to insert the same value more then once.

so basiccly you will have ask the DBA at your company to update the table script foryou and it will do the work for you.

if you want to check it manually you will have to do the select yourself.

execute the select FILED_NAME from ... bla bla bla

and if the resaultSet you get in return is empty you dont have any data regards to this value.
else you can do your insert.

hardraksAuthor Commented:
So can u be more specific on the manual
execute the select FILED_NAME from ... bla bla bla

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the steps you have to do are the following:
1. declare the needed field as primary Key in the database (ask your dba how to do it or if you dont know any ill explain to you how to do it). doing this will insure that this column CANNOT contains 2 identical values. each try to insert value that already exist will throw exception by oracle (parent key vioalted exception or something like that). you will have to see in your application if you can insert same start date with diffrent end date (it can be done too by declaring the start date AND end date as the key for the table so those 2 columns will have to be unique.

2. after doing that you have 2 options:
A. execute a select query on the table (select * from SUB_TABLE where START_DATE=[your value]. if you will get resault with values it means that you already has a record.
B. try to insert the data as you did before and you will get the exception i explained before.

if you need any thing else just ask me.

hardraksAuthor Commented:
Thanks for your comments i'm working on it...If any issue i shall shoot back...
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Answered by: Nushi
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