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How do I delete a row or amend an element in a CSV file using Java?

I'm trying to create a csv file with names and ID numbers in order to create individual users. It is also used to identify whether an user has admin status or not (boolean). If I accidentally input a user as an admin when they are not, how can I delete that user or edit his status? I am using an array list. Thanks.
I've included my load method for any clarification needed. I'm new to Stack Overflow so please excuse any formatting errors.
public static void load() throws IOException
{
System.out.println("<<< Loading users >>>");
File userFile = new File("user.csv");
if (!userFile.exists())
{
userFile.createNewFile();
System.out.println("Data file not found.");
add(); // or go and add an item -->addItem()
}
FileReader fr = new FileReader(userFile);
BufferedReader in = new BufferedReader(fr); //read mode
String newfirstName = "";
int newSchool_ID = 0;
String admin = "Y";
String isAdmin = "";
boolean newisAdmin = false;
String temp;
users.clear();
temp = in.readLine(); // read the heading and ignore it
while (in.ready()) // read lines while file has content
{
newisAdmin = false;
temp = in.readLine();
String[] line = temp.split(",");
newfirstName = line[0];
newSchool_ID = Integer.parseInt(line[1]);
if(admin.equals(line[2])){
isAdmin = "Admin";
newisAdmin = true;
}
User newUser = new User(newfirstName, newSchool_ID, newisAdmin);
users.add(newUser);
}
in.close();
System.out.println("User loaded.");
}

Java split ignoring white space [closed]

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so, let's say that i have this code
String some = ("my name|username|password");
String[] split = some.split("|");
i want to have a string like this
split[0] = "my name";
split[1] = "username";
split[0] = "password";
here is my code
String record = null;
FileReader in = null;
MainMenu menu = null;
public void checkLogin() throws FileNotFoundException, IOException, ArrayIndexOutOfBoundsException {
in = new FileReader("D:\\Login.txt");
BufferedReader br = new BufferedReader(in);
String username = txfUsername.getText();
String password = new String(txfPassword.getPassword());
while ((record = br.readLine()) != null) {
String[] split = record.split("-");
if (username.equals(split[1]) && password.equals(split[2])) {
JFrame frame = new JFrame();
menu = new MainMenu(split[0]);
this.setVisible(false);
menu.setVisible(true);
break;
}
}
if (menu == null) {
JOptionPane.showMessageDialog(null, "Username or Password wrong.");
}
}
and here is login.txt
my name-user-pass
when i run the program it will throw arrayindexoutofbound exception
how to get rid of that?

In my opinion, when dealing with a text file you want to always make sure you are actually processing a data line especially if your app is not responsible for creating the text file. You should also always be aware of the fact that the data line may not contain all the required data so as to eliminate the possibility of encountering a ArrayIndexOutOfBoundsException when utilizing the String.split() method.
You may also want to allow for a mechanism to handle comment lines within the text file so that some can be added. These lines would of course be ignored as would blank lines. In this case the text file path and file name is hard coded within the method but if the file was to be User selectable via a JFileChooser (or whatever) it would be good if the very first line of the file was a comment line indicating what the file is for, for example:
;MyAppName Login Data
;Real Name, Login Name, Password
John Doe, johnnyboy, cGFzczEyMzQ
Bill Smith, BoperBill, U3VwZXJDb29sMQ
Tracey Johnson, tracey, NzcyMzQ2Ng
Fred Flinstone, PebblesDaddy, V2lsbWEnc19EdWRl
In the example file layout above, lines that start with a semi-colon (;) are considered comment lines. The very first comment is the File Descriptor. When the file is read then this line is checked and if it states what is expected then you know for a fact that it is most likely a correct text file to process otherwise the User supplied or selected a wrong text file.
You will notice that the passwords are encrypted. Not even you should know what they are. Passwords are private to the User only. A simple Base64 Encryption is used here (Java 8+ required) but only for example purposes. It may be good enough for a some applications but definitely not for all, but still, something is better than nothing at all.
To encrypt a password in Base64 in your case you might use (import java.util.Base64 required):
String password = Base64.getEncoder().withoutPadding().
encodeToString(String.valueOf(txfPassword.
getPassword()).getBytes());
Do this before saving the User Password to file.
Here is how your checkLogin() method might look:
public void checkLogin() throws FileNotFoundException, IOException {
// Try with Resources...This will auto-close the BufferReader.
try (BufferedReader br = new BufferedReader(new FileReader("D:\\Login.txt"))) {
// Install code here to validate that txfUsername and txfPassword
// text boxes actually contain something. Exit method if not.
// ................................
String userName = txfUsername.getText();
// Encrypt supplied password and compare to what is in file
String password = Base64.getEncoder().withoutPadding().encodeToString(String.valueOf(txfPassword.getPassword()).getBytes());
if (userName.equals("") || password.equals("")) {
return;
}
String line;
int lineCounter = 0;
boolean loginSuccess = false;
while ((line = br.readLine().trim()) != null) {
lineCounter++;
// Is this the right data file?
if (lineCounter == 1 && !line.equals(";MyAppName Login Data")) {
JOptionPane.showMessageDialog(this, "Wrong Text File Supplied!",
"Invalid Data File", JOptionPane.WARNING_MESSAGE);
return;
}
// Skip blank and comment lines...
if (line.equals("") || line.startsWith(";")) { continue; }
// Split the comma/space delimited data line (", ")
String[] lineSplit = line.split(",\\s+"); // \\s+ means 1 or more spaces
// make sure we have three array elements
if (lineSplit.length == 3 && userName.equals(lineSplit[1]) && password.equals(lineSplit[2])) {
loginSuccess = true;
JFrame frame = new JFrame();
menu = new MainMenu(lineSplit[0]);
this.setVisible(false);
menu.setVisible(true);
break;
}
}
// Can't find login name or password in file.
if (!loginSuccess) {
JOptionPane.showMessageDialog(this, "Invalid User Name or Password!",
"Invalid Login", JOptionPane.WARNING_MESSAGE);
}
}
}

Reading from a text file and Matching user input to certain field columns in the text file. Columns are delimited

I'm creating a menu based console application using Java. I have a class that allows the user to sign up by inputting their information. This information is written to a file that is appended each time a new user is entered.
I would like to have a login function, but I'm having trouble figuring out how to read the file and only match the user input to the first two columns ID;Password.
Once they match the user input, I'll be able to continue to the next menu.
My text file looks like this:
ID;Password;FirstName;LastName;Email
admin;1234;adminFirst;adminLast;adminMail#admin.com
Here's my Login class as well. I created an array for user input, just in case that would be useful:
public class Log_In extends Main_Menu {
public void logging_in(){
Scanner in = new Scanner(System.in);
System.out.println("Please enter your login information!");
String [] log_in_array = new String[2];
String ID, password;
System.out.print("ID: ");
ID = in.next();
System.out.print("Password: ");
password = in.next();
//Stores the ID and PASSWORD to the array. Now we will compare the array to the txt file to find a match
//Must match FIELD_ONE;FIELD_TWO
log_in_array [0] = ID;
log_in_array [1] = password;
in.close();
}
}

you can write helper method to read your text file and compare id and password provided by user, like following.
// The name of the file to open.
static String fileName = "myTextFliel.txt";
public static boolean myHelper(String id, String password) {
// This will reference one line at a time
String line = null;
boolean retVal= false;
try {
// FileReader reads text files in the default encoding.
FileReader fileReader =
new FileReader(fileName);
// Always wrap FileReader in BufferedReader.
BufferedReader bufferedReader =
new BufferedReader(fileReader);
while((line = bufferedReader.readLine()) != null) {
//create a token based on
String [] token=line.split(";");
// because you know first and second word of each line in
// given file is id and password
if (token[0].equals(id) && token[1].equals(password)){
retVal=true;
return retVal;
}
}
// Always close files.
bufferedReader.close();
}
catch(FileNotFoundException ex) {
System.out.println(
"Unable to open file '" +
fileName + "'");
}
catch(IOException ex) {
System.out.println(
"Error reading file '"
+ fileName + "'");
// Or we could just do this:
// ex.printStackTrace();
}
return retVal;
}
public void logging_in(){
Scanner in = new Scanner(System.in);
System.out.println("Please enter your login information!");
String [] log_in_array = new String[2];
String ID, password;
System.out.print("ID: ");
ID = in.next();
System.out.print("Password: ");
password = in.next();
//Stores the ID and PASSWORD to the array. Now we will compare the array to the txt file to find a match
//Must match FIELD_ONE;FIELD_TWO
log_in_array [0] = ID;
log_in_array [1] = password;
// Here you can call your helper method.
boolean foundMe =myHelper(log_in_array [0],log_in_array [1])
if (foundMe==true){
//do whatever u want to do
}
in.close();
}
With little bit of more work you can ignore header line.

If the structure of the file is something like this
username pass data data
username pass data data
username pass data data... and so on
you can read the file into an ArrayList, but skip everything that isn't a user name or pass like so
ArrayList<String> userinfo = new ArrayList();
while (input.hasNext()){ //input is a Scanner object that is your file
userinfo.add(input.next());//username
userinfo.add(input.next());//pass
input.next();//skip
input.next();//skip
}
every username and password will be in pairs like this within the
ArrayList
(username, pass, username, pass, username, pass,...)
Then to see if a username and password matches
int index = userinfo.indexOf(ID);
if (userinfo.get(index+1).equals(password))//the password comes right after the username in the list
return true;
I'm assuming this is for practice, you would typically use a database of some sort for user name and passwords

Create simple login based on txt file

Cannot understand why following code doesn't work properly. Firstly, system getting input from the user. Then system reads all data from .txt file and compare with the user input. But the system never finds similar username and password.
The idea is to create simple login that based on the stored username and password in .txt file. Could someone help?
private static void login() {
String record = null;
FileReader in = null;
try {
in = new FileReader("adminlogin.txt");
BufferedReader br = new BufferedReader(in);
Scanner keyboard = new Scanner(System.in);
System.out.print("Username: ");
String user = keyboard.nextLine();
System.out.print("Password: ");
String pass = keyboard.nextLine();
while ((record = br.readLine()) !=null) {
if (user.equals(record) && pass.equals(record)) {
Mainemenu menu = new Mainemenu();
menu.AdminMenu();
} else {
System.out.println("________----Error----________\n press 'Enter' to continue...");
keyboard.nextLine();
checkInput();
}
}
} catch (IOException e) {
e.getCause();
}
}

Your problem is the loop and its comparison:
while ((record = br.readLine()) !=null) {
if (user.equals(record) && pass.equals(record)) {
//...
}
//...
}
You read a whole line from your file, which is in record, but then you compare both user and pass with this line. This will never work, except user is equal to pass.
Either you have stored the user name and password in a line in your file - then you have to split the line into user name and password - or you have the name and password stored in two separate lines - then you need to reads in the loop for each user.
Moreover, you do throw an error after you checked only the first user and you do not exit the loop, if you actually found the user.
Solutions
I suppose your records in the file are like "username password", then do:
Mainemenu menu = null;
while ((record = br.readLine()) !=null) {
// Split line by a whitespace character
// split[0] <- username
// split[1] <- password
String[] split = record.split("\\s");
if (user.equals(split[0]) && pass.equals(split[1])) {
menu = new Mainemenu();
menu.AdminMenu();
// You found the user, exit the loop
break;
}
// Delete else branch
}
if (menu == null) {
// User not found
}
Of course you can use any other delimiter character or sequence for your records by adopting the delimiter string in split.

File handling: Loop through text file and continually compare parameters

I'm looping through text file and need to compare the contents of the text file to parameters being submitted by a user. The code I've written so far will only compare the last value in the text file.
Question: How would I continually loop and check the contents V parameters passed, stopping when there's a match between the two?
Here's what I have so far:
public boolean isAuthenticated(String username, String password) throws FileNotFoundException{
boolean status = true;
File file = new File("C:\\" "\\" "\\login.txt");
Scanner scan = new Scanner(file);
List<Login> login = new ArrayList<Login>();
while(scan.hasNextLine()){
String line = scan.nextLine();
String [] details = line.split(":");
String storedUsername = details[0];
String storedPassword = details[1];
Login l = new Login(username, password);
if(storedUsername.equals(username)&& storedPassword.equals(password)){
status = true;
}else{
status = false;
}
}
return status;
}
Thanks! Query6273

Your code does compare every line of the file to the username and password. But at each iteration, you replace the previous value of status with the status of the current line.
So you end up returning the status of the last line.
You need to break out of the loop as soon as you found the user you were looking for. For example:
while (scan.hasNextLine()) {
...
if (storedUsername.equals(username) && storedPassword.equals(password)) {
return true;
}
}
or
// we haven't found the user yet, so status is false
boolean status = false;
while (scan.hasNextLine() && !status) {
...
if (storedUsername.equals(username) && storedPassword.equals(password)) {
status = true;
}
}
return status;
Note that the Scanner should be closed properly. You should use try-with-resources.