Java file username check

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I am having a file called customersinfo.txt this is how my file structure looks like

ID FirstName LastName Email Mobile UserName PassWord ConPassWord 1 John Sam JS@gmail.com 0123 JhonSam12 1234 1234 2 ---- ------ ----------- ---- ----- ------ -------

So my problem is it accepts multiple users with the same username what I want is to check when the customer enters his username whether if that username already exists in the file or not if that username already exists try to enter a different username if not accept and save it to the file

What I have tried:

Java

package sample;

import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Scene;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

import javax.swing.*;
import java.io.*;
import java.nio.file.Files;
import java.util.Collection;
import java.util.Scanner;
import java.util.stream.Collectors;

public class Read
{
    public void display ()
    {
        String filepath = "customersAllInfo.txt";
        String editTerm = "343";
        String newFirstName = "1";
        String newLastName = "1";
        String newEmailID = "1";
        String newMobile = "1";
        String newPassword = "1";
        String newPasswordCon = "1";

        CreatNewUser(filepath,newFirstName,newLastName,newEmailID,newMobile,editTerm,newPassword,newPasswordCon);
    }

    private static Scanner x;

    public void CreatNewUser (String filepath,String newFirstName,String newLastName,String newEmailID,String newMobile,String editTerm,String newPassword,String newPasswordCon)
    {
        boolean found = false;
        File newCustomer = new File("customersAllInfo.txt");
        File oldFile = new File(filepath);
        String IDF1 = ""; String saveFname1 = ""; String saveLname1 = ""; String saveEmail1 = ""; String saveMobile1 = ""; String saveUser1 = "";
        String saveFpass1 = ""; String saveLpass1 = "";
        try
        {
            x = new Scanner(new File(filepath));
            x.useDelimiter("[,\n]");

            while (x.hasNext() && !found)
            {
                IDF1        = x.next();
                saveFname1  = x.next();
                saveLname1  = x.next();
                saveEmail1  = x.next();
                saveMobile1 = x.next();
                saveUser1   = x.next();
                saveFpass1  = x.next();
                saveLpass1  = x.next();

                if (saveUser1.trim().equals(editTerm.trim()))
                {
                    //found = true;
                    System.out.println("Already Exists");
                    found = true;
                }

                else
                {
                    newCustomer = new File("customersAllInfo.txt");
                    try
                    {
                        newCustomer.createNewFile();
                    }
                    catch (IOException ex)
                    {
                        System.out.println("customersAllInfo FILE COULDN'T BE CREATED");
                    }

                    try
                    {
                        BufferedWriter a = new BufferedWriter(new FileWriter(newCustomer,true));
                        a.write( newFirstName + "," + newLastName + "," + newEmailID + "," + newMobile + editTerm + "," + newMobile + "," + newPassword + "," + newPasswordCon + "\n");
                        a.close();
                        System.out.println("DONE");
                    }
                    catch (IOException ex)
                    {
                        System.out.println("ERROR IN ENTERING THE INFORMATION");
                    }

                }
                }
            x.close();
        }
        catch (Exception e)
        {
            System.out.println("ERROR ERROR TO FIND FILE");
        }

    }
}

Posted 18-Mar-20 1:45am

yusof26

Updated 18-Mar-20 7:26am

Richard MacCutchan

v2

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Comments

Richard MacCutchan 18-Mar-20 8:30am

Why not use a database rather than a text file? It makes it easy to check for duplicates.

yusof26 18-Mar-20 9:58am

I do agree with you but it is an assignment and database is not allowed

Richard MacCutchan 18-Mar-20 12:10pm

OK, that's fine.

That means that you will need to read the entire file each time. As you read the file, create a list (see the Java collection types) that maps the username to the remaining details. You can then do a quick lookup on the list to see if a username already exists. If you cannot use a collection class then you can still use a simple array, although you will need to write all the search code for yourself.

yusof26 18-Mar-20 13:10pm

Thanks a lot for the great tip

Richard MacCutchan 18-Mar-20 13:24pm

You are welcome.

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OriginalGriff · Accepted Answer · 2020-03-18T01:57:00

The simplest way is to add a second file (or format your file so it contains an extra table)
This second file is an index file, and it contains two bits of info:
A hashcode - the username, hashed with MD5 or SHA (MD5 is officially broken, but it's fine for non-security applications like this)
An index - the position in the original file at which the user record begins.

Read the index file into memory - it's not massive - and when you need to find or check a username, you hash it, find the hash in your memory index table. If it's there, compare the actual strings - hash collisions are rare, but they do happen - it they are the same, it's the same username. It's probably even acceptable just to reject a username if the hash is a collision!

The advantage of this approach is that all the records in the index file are the same size: the hash size plus an integer index - so it's trivial to read, and trivial to compare, unlike variable length usernames and rows - and hashing is pretty quick.