Java中使用Swing进行文件处理编程

Question

I need help with step 2 to understand the working of File handling in java,,,,...

This is what i am doing.... :- problem: Exception Note: i am a newbie with this concept to please tell me what is wrong in my code.

-Create a mini Java application using swing, which must ask for a Username and Password and have a create button.

-as soon as the create button is pressed a new directory must be created with the name of the user and password must be saved as password.txt file inside that directory.

-if the directory already exists, then a pop-up windows should appear saying "User already exists".

I've tried for hours now but can't do it properly, little help is much appreciated.

I need to see some code for this, while i am continuously trying to fix mine.

Updated Code :

import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
import java.io.*;

class CreateUser implements ActionListener
{   
    JFrame fr;  //Frame
    JButton b1;  //Create Button
    JLabel lb1, lb2;    //Username and password
    JTextField tf1, tf2;    //Username and password input fields
    JPanel p1;

    CreateUser()
    {
        //Setting the frame
        fr=new JFrame();
        fr.setLayout(null);
        fr.setSize(400,400);

        //setting panel
        p1=new JPanel();
        p1.setBounds(0,0,400,400);
        p1.setLayout(null);

        //setting Username Label
        JLabel lb1=new JLabel("Username: ");
        lb1.setBounds(50,50,70,30);
        p1.add(lb1);

        //setting Username Text Field
        JTextField tf1 = new JTextField();
        tf1.setBounds(150,50,150,30);
        p1.add(tf1);


        //setting Password Label
        JLabel lb2=new JLabel("Password: ");
        lb2.setBounds(50,100,70,30);
        p1.add(lb2);

        //setting Password Text Field
        JTextField tf2 = new JTextField();
        tf2.setBounds(150,100,150,30);
        p1.add(tf2);

        //setting Button
        b1=new JButton("Create");
        b1.setBounds(100,200,100,40);   
        p1.add(b1);

        fr.add(p1);
        fr.setVisible(true);    
        b1.addActionListener(this);
        tf1.addActionListener(this);
        tf2.addActionListener(this);

    }

    public static void main(String s[])
    {
        new CreateUser();
    }

    public void actionPerformed(ActionEvent e)
    {
        if(e.getSource()==b1)
        {   
            {
                String uid = tf1.getText();
                String pass = tf2.getText();

                String dir = System.getProperty("user.dir");

                //Creating a new folder Users

                File file = new File(dir+"\\users");
                if (!file.exists()) 
                {
                    if (file.mkdir()) 
                    {
                        System.out.println("Directory is created!");
                    } 
                    else 
                    {
                        System.out.println("Failed to create directory!");
                    }
                }
                dir = dir+"\\users";

                //Creating a folder named with username inside Users folder

                File file1 = new File(dir+"\\"+uid);
                if (!file1.exists()) 
                {
                    if (file1.mkdir()) 
                    {
                        System.out.println("Directory is created!");
                    } 
                    else 
                    {
                        System.out.println("Failed to create directory!");
                    }
                }

                //Storing Password.txt inside users/username folder

                try
                {
                    FileOutputStream fout=new FileOutputStream("password.txt");
                    byte b[]=pass.getBytes();
                    fout.write(b);
                }
                catch(Exception ee)
                {}
            }
        }
    }           
}

Answer 1

Many potential problems here so let's go through the code:

class CreateUser implements ActionListener {

Minor problem: avoid having your GUI classes implement your control interfaces. This gives the class too much responsibility, cluttering the class, leading to unwieldy difficult to debug code. Better to use an anonymous inner class or non-anonymous inner class.

JFrame fr; // Frame
JButton b1; // Create Button
JLabel lb1, lb2; // Username and password
JTextField tf1, tf2; // Username and password input fields
JPanel p1;

Minor problem: the fields should always be private unless you've a specific reason to make the public. You don't, so make them private here.

CreateUser() {
    // Setting the frame
    fr = new JFrame();
    fr.setLayout(null);
    fr.setSize(400, 400);

Minor problem: Never, never, never use null layouts. While null layouts and setBounds() might seem to Swing newbies like the easiest and best way to create complex GUI's, the more Swing GUI'S you create the more serious difficulties you will run into when using them. They won't resize your components when the GUI resizes, they are a royal witch to enhance or maintain, they fail completely when placed in scrollpanes, they look gawd-awful when viewed on all platforms or screen resolutions that are different from the original one.

    // setting panel
    p1 = new JPanel();
    p1.setBounds(0, 0, 400, 400);
    p1.setLayout(null);

Same problem. Learn the layout managers, and then use the layout managers.

    // setting Username Text Field
    JTextField tf1 = new JTextField();

Major problem : You're shadowing a field here. By re-declaring the tf1 variable within the class constructor, you're assigning a JTextField object to a local variable, which means that the tf1 field in the class remains empty/unassigned/null. This can lead to a NullPointerException being called if you ever try to use this null field.

So if you're going to do the object creation and assignments within the constructor or an init method, then instead of

    JTextField tf1 = new JTextField();

do:

    tf1 = new JTextField(); 


    // setting Password Text Field
    JTextField tf2 = new JTextField();

Same problem. Also this should be a JPasswordField not a JTextField.

    // setting Button
    b1 = new JButton("Create");

For some reason you assign the button correctly. Go figure.

public static void main(String s[]) {
    new CreateUser();
}

Always start a Swing application on the Swing event thread or EDT (for Event Dispatch Thread). So do:

public static void main(String s[]) {
    SwingUtilities.invokeLater(() -> new CreateUser());        
}

---

try {
    FileOutputStream fout = new FileOutputStream("password.txt");
    byte b[] = pass.getBytes();
    fout.write(b);
} catch (Exception ee) {

}

Major problem: never never have an empty catch block which is the coding equivalent of trying to drive a car with a blindfold on. At least print out the stacktrace so you will be notified of errors if and when they occur. Also, if you're writing out text, use a writer such as a PrintWriter. I won't go into the dangers of writing out password text, but obviously it's something you'd never do in real life.