Splitting Contents of a File

Question

So I have a file with a list of users in the format like this:

michael:atbWfKL4etk4U:500:500:Michael Ferris:/home/michael:/bin/bash abigail:&i4KZ5wmac566:501:501:Abigail Smith:/home/abigail:/bin/tcsh

What I need to do is just extract the passwords from the file which in this case are: "atbWfKL4etk4U" and "&i4KZ5wmac566" and to store them into an array.

This is what I have so far:

public static void main(String[] args) throws IOException{
    
    // Create a scanner for keyboard input
    Scanner scan = new Scanner(System.in);
    
    // Prompt user to select a file to open
    System.out.print("Enter the path of the file: ");
    String filename = scan.nextLine();
    
    // Open the file
    File file = new File(filename);
    Scanner inputFile = new Scanner(file);
    
    // Create Array to store each user password in
    String[] passwords = {};
    

    
    // Close the file
    scan.close();
    inputFile.close();
    

}

Answer 1

public static void main(String[] args) throws IOException{
    
    // Create a scanner for keyboard input
    Scanner scan = new Scanner(System.in);
    
    // Prompt user to select a file to open
    System.out.print("Enter the path of the file: ");
    String filename = scan.nextLine();
    
    // Open the file
    File file = new File(filename);
    Scanner inputFile = new Scanner(file);

    List<String> passwords = new ArrayList<>();
    while (sc.hasNextLine()) {
        String line = sc.nextLine();
        String password = line.split(":")[1];
        passwords.add(password);
    }
    // Close the file
    scan.close();
    inputFile.close();
}

If instead you rather store username and password (assuming the first token is the user name), create a Map instead of a List.

Map<String, String> passwordMap = new HashMap<>();
while (sc.hasNextLine()) {
   String line = sc.nextLine();
   String[] tokens = line.split(":");
    passwordMap.put(tokens[0], tokens[1]);
}

Answer 2

You could read the file line by line using a Scanner object. Then, you use another Scanner object to read the password. Here's an example:

String input = "michael:atbWfKL4etk4U:500:500:Michael Ferris:/home/michael:/bin/bash";
Scanner s = new Scanner(input).useDelimiter(":");
s.next();  //skipping username
String password = s.next();

Answer 3

This looks like a typical CSV type file format and because there is an unknown number of Users in the file and the fact that arrays can not dynamically grow it's a good idea to utilize an ArrayList which can grow dynamically and then convert that list to a String array, for example:

The following method assumes there is No Header Line within the data file:

public static String[] getPasswordsFromFile(String filePath) {
    List<String> passwordsList = new ArrayList<>();
    File file = new File(filePath);
    try (Scanner reader = new Scanner(file)) {
        String line = "";
        while (reader.hasNextLine()) {
            line = reader.nextLine().trim();
            // Skip blank lines (if any).
            if (line.isEmpty()) {
                continue;
            }
            /* Split out the password from the file data line:
               The Regular Expression (RegEx) below splits each
               encountered file line based on the Colon(:) delimiter
               but also handles any possible whitespaces before 
               or after that delimiter:                 */
            String linePassword = line.split("\\s*\\:\\s*")[1];
            
            // If there is no password there then apply "N/A":
            if (linePassword.isEmpty()) {
                linePassword = "N/A";
            }
            // Add the password to the List
            passwordsList.add(linePassword);
        }
    }
    catch (FileNotFoundException ex) {
        // Handle the exception (if any) the way you like...
        System.err.println(ex.getMessage());
    }
    
    // Convert the List<String> to String[] Array and return:
    return passwordsList.toArray(new String[passwordsList.size()]);
}

How you might use a method like this:

// Create a scanner object for keyboard input
Scanner userInput = new Scanner(System.in);
    
// Prompt user to select a file to open with validation:
String fileName = "";
// -----------------------------------
while (fileName.isEmpty()) {
    System.out.print("Enter the path of the file (c to cancel): --> ");
    fileName = userInput.nextLine();
    if (fileName.equalsIgnoreCase("c")) {
        System.out.println("Process Canceled! Quiting.");
        System.exit(0);
    }
    if (!new File(fileName).exists()) {
        System.out.println("Invalid Entry! Try again...\n");
        fileName = "";
    }
}
// -----------------------------------
    
/* OR - you could have........    
// -----------------------------------
javax.swing.JFileChooser fc = new javax.swing.JFileChooser(new File("").getAbsolutePath());
fc.showDialog(new JDialog(), "get Passwords");
if (fc.getSelectedFile() != null) {
    fileName = fc.getSelectedFile().getAbsolutePath();
}
else {
    System.out.println("Process Canceled! Quiting.");
    System.exit(0);
}
// -----------------------------------
*/
        
// Get the Passwords from file:        
String[] passwords = getPasswordsFromFile("UserData.txt");
// Display the Passwords retrieved:
System.out.println();
System.out.println("Passwords from file:");
System.out.println("====================");
    
for (String str : passwords) {
    System.out.println(str);
}

If you were to run this code against a file which contains the data you provided within your post,your console window will diplay:

Enter the path of the file (c to cancel): --> userData.txt

Passwords from file:
====================
atbWfKL4etk4U
&i4KZ5wmac566