Java GUI Swing, reading from .txt file

Question

Okay, I was wondering if someone can explain, in great detail, how to make my JPasswordField save the contents that where entered into it, into a .txt file. So when I open the program again, I can have that person log in and it will get if thats the password or not. If it is the password, then the JOptionPane will close. I have this all in a JFrame, and the "Log In" button is in a JMenuBar in a JMenu, named "File". In the text file, I'd like to have the user enter a username and password, and it will set a username and a password to that user, like this. ex.

Username = Gavin

Password = 123

So if there are ways of just storing a certain variable, to that text file and make the program load that variables value, it'd be great if you can explain. I am also very open to spoonfeeding because I don't just take and use it, no. I'm going to look at it, figure out why it works because I'm going to work on duplicating it in a different way. Thanks in advance!

P.S. Yes, I did do some research, but the problem is, people would put a code that I have no clue on how it may start to work, I am farely new to Java programming. So, please do paste codes, I will study them, but if you can also throw in a minor explanation.

Answer 1

I believe this is exactly what you are looking for - http://cs.saddleback.edu/rwatkins/CS4B/Crypto/FileEncryptor.html

The code is well documented but if you have any questions just ask them and I'll try to answer them

Well that is the simplest way (probably) to do it using encryption. Which is definitely a good idea. However the simple part of just writing and reading to a text file can be done by

39:       filename = "clear.txt";
40: 
41:       // Password must be at least 8 characters (bytes) long
42: 
43:       String password = "super_secret";
44: 
46:       outFile = new FileOutputStream(filename);
80:       outFile.write(password);

and this method to read which is more complicated but i will try to explain it

private static String readFileAsString(String filePath) throws java.io.IOException{
    byte[] buffer = new byte[(int) new File(filePath).length()];
    BufferedInputStream f = null;
    try {
        f = new BufferedInputStream(new FileInputStream(filePath));
        f.read(buffer);
    } finally {
        if (f != null) try { f.close(); } catch (IOException ignored) { }
    }
    return new String(buffer);
}

Basically byte[] is an array (google it if your not sure what that is) of raw 1s and 0s. It puts all the 1s and 0s of the file into and array (that is the same length as the file i.e. (int) new File(filePath).length()) Then a fileinputstream does all the wonderful magic to turn these 1s and 0s into text. The BufferedinputStream is just an efficient wrapper for the fileinputstream because it reads lots of bytes at one time then converts them all at the same time (it stores them in a buffer hence the name) versus reading and converting 1 byte at a time which is slow and inefficient (FileInputStream by itself). The exceptions youll want to google but basically it's just so your program doesn't crash if you cant find the file or you don't have permissions to read/write from it.