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I'm 16 years old and no one to help me, no one to give any advice or constructive criticism, I'm aimless. I'll leave the link to my last code (github), a program that sends an email to everyone registered in the database. I would like some advice and project/content ideas for me to evolve. Evaluate my project sincerely.

UPDATE: According to the last suggestion (in the last post), the program was very dependent, not following the S.O.L.I.D concepts, one class was doing all the work, so I created 2 more classes to divide the functions (FactoryConnection and DAO).

Class DAO, this class is responsible for creating the SELECT statement (MySql) that connects to return users:

package project;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class DAO {
    
    static Connection conn;
    static ResultSet users;
    static PreparedStatement ps;
    
    
    protected static ResultSet retriveUsers() {
        FactoryConnection.closeConnections(conn, ps, users);    // if there is any new connection, it will close the previous one
        
        try { 
            conn = FactoryConnection.getConnectionToMySql();
            ps = (PreparedStatement) conn.prepareStatement("select * from users");
            users = ps.executeQuery();
        
            return users;
            
        } catch (Exception e) {
            e.printStackTrace();
        } 
        
        return null;
    }
}

Class FactoryConnection, this class will create the connection to MySql (getConnectionToMySql)database and close the connections (closeConnections) when called:

package project;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import org.apache.commons.dbutils.DbUtils;

public class FactoryConnection {
    
    protected static Connection getConnectionToMySql() throws SQLException {
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/emailproject?useTimezone=true&serverTimezone=UTC", "root", "");
        return conn;
    }
    
    protected static void closeConnections(Connection conn, PreparedStatement ps, ResultSet users) {
        DbUtils.closeQuietly(conn);
        DbUtils.closeQuietly(users);
        DbUtils.closeQuietly(ps);
    }
}

Class JavaMailUtil, this class will send the email to the users (using the DAO class to get the users in database):

package project;

import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.mail.Authenticator;
import javax.mail.Message;
import javax.mail.PasswordAuthentication;
import javax.mail.Session;
import javax.mail.Transport;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import javax.swing.JOptionPane;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;


public class JavaMailUtil {
    
    Connection conn;
    PreparedStatement ps;
    ResultSet rs;
    String sender = "[email protected]";
    String senderPassword = "******";

    
    public void sendEmail(String title, String text) {  
        try {
            ResultSet users = DAO.retriveUsers();
            
            while (users.next()) {
                Properties prop = new Properties();
                prop.put("mail.smtp.auth", true);
                prop.put("mail.smtp.starttls.enable", "true");
                prop.put("mail.smtp.host", "smtp.gmail.com");
                prop.put("mail.smtp.port", "587");
                
                Session session = Session.getInstance(prop, new Authenticator() {
                    @Override
                    protected PasswordAuthentication getPasswordAuthentication() {
                        return new PasswordAuthentication(sender, senderPassword);
                    }       
                });
                
                Message message = prepareMessage(session, sender, users.getString(2), text, title);
                
                Transport.send(message);
            }
            
        } catch (Exception e) {
            JOptionPane.showMessageDialog(null, "Error!");
            e.printStackTrace();
            return;
        } 
        
         JOptionPane.showMessageDialog(null, "Email successfully sent!");
    }

    
    private static Message prepareMessage(Session session, String sender, String recepient, String text, String title) {
        try {
            Message message = new MimeMessage(session);
            message.setFrom(new InternetAddress(sender));
            message.setRecipient(Message.RecipientType.TO, new InternetAddress(recepient));
            message.setSubject(title);
            message.setText(text);
            return message;
            
        } catch (Exception e) {
            Logger.getLogger(JavaMailUtil.class.getName()).log(Level.SEVERE, null, e);
        }
        return null;
        
    }
}

Swing Part, the main class that will call the codes:

package windows;

import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextField;

import project.JavaMailUtil;

import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.Font;
import javax.swing.JTextArea;
import javax.swing.SwingConstants;

public class MainWindow {

    private JFrame frame;
    private JTextField txtTitle;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    MainWindow window = new MainWindow();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public MainWindow() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    public void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);
        frame.setLocationRelativeTo(null);
        
        JLabel lbl1 = new JLabel("Title:");
        lbl1.setFont(new Font("Tahoma", Font.PLAIN, 18));
        lbl1.setBounds(10, 81, 43, 26);
        frame.getContentPane().add(lbl1);
        
        JLabel lbl2 = new JLabel("Text:");
        lbl2.setFont(new Font("Tahoma", Font.PLAIN, 18));
        lbl2.setBounds(10, 133, 43, 26);
        frame.getContentPane().add(lbl2);
        
        txtTitle = new JTextField();
        txtTitle.setHorizontalAlignment(SwingConstants.CENTER);
        txtTitle.setFont(new Font("Tahoma", Font.BOLD, 15));
        txtTitle.setBounds(54, 77, 342, 37);
        frame.getContentPane().add(txtTitle);
        txtTitle.setColumns(10);
        
        JButton buttonSend = new JButton("Send Email");
        buttonSend.setFont(new Font("Tahoma", Font.PLAIN, 16));
        buttonSend.setBounds(269, 227, 127, 23);
        frame.getContentPane().add(buttonSend);
        
        JTextArea txtText = new JTextArea();
        txtText.setFont(new Font("Tahoma", Font.BOLD, 15));
        txtText.setBounds(54, 136, 342, 80);
        frame.getContentPane().add(txtText);
        txtText.setLineWrap(true);
        txtText.setWrapStyleWord(true);
        
        JLabel lblNewLabel = new JLabel("Automatic Sender");
        lblNewLabel.setFont(new Font("Tahoma", Font.BOLD | Font.ITALIC, 23));
        lblNewLabel.setBounds(95, 22, 243, 37);
        frame.getContentPane().add(lblNewLabel);
        
        JButton buttonUsers = new JButton("Users");
        buttonUsers.setFont(new Font("Tahoma", Font.PLAIN, 16));
        buttonUsers.setBounds(54, 227, 83, 23);
        frame.getContentPane().add(buttonUsers);
        

        
        // TODO

        buttonSend.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                JavaMailUtil javaMailUtil = new JavaMailUtil();

                buttonSend.setText("Sending...");
                JOptionPane.showMessageDialog(null, "Sending... Wait the alert!");
                
                javaMailUtil.sendEmail(txtTitle.getText(), txtText.getText());
                buttonSend.setText("Send Email");
            }
        });
    
    }
}

GitHub Link: https://github.com/DaviRibeiro-prog/JAVA/tree/main/EmailSenderProject/src

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1 Answer 1

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That's already a nice improvement. However there is a lot of static in your code. static is the "Uncle Ben" keyword; it has "great power but induce great responsibilities".

Think back to the Open Closed principle of solid. How can I use a local file, or my favourite mail client address book instead of a MySQL database ?

It would be great to add some abstractions. Why not one AddressBook interface:

interface AddressBook extends Iterable<String>

That interface will be used anywhere that you want to access retrieve your contacts. But because it is an interface you cannot statically access it (in fact you can but let's forgot about that). You should dynamically pass an instance of that AddressBook to your JavaMailUtil, and the constructor is the perfect candidate for that :

class JavaMailUtil {
  JavaMailUtil(AddressBook contacts) {
    this.contacts = contacts;
  }

  // When sending
  contacts.forEach(contact -> {
    // Your sending logic.
  });
}

You should try to remove all static keywords from your code and see how it will improve your program by allowing you to easily switch the implementations. Let's do it for the DAO so that you can reuse it for a MySql or MariaDb or any other compliant database.

class ContactsDao {
  public ContactsDao(ConnectionFactory conns) {
    this.conns = conns;
  } 
}

Do you remember the Interface Seggregation principle ?

One thing with the DAO is that it returns a ResultSet. If I want to swap your DAO with a file, I have to convert my lines to a ResultSet. This will be annoying, error prone and useless because I should have to implement methods that are never used. So it is better to find a simpler model for iterating over all your contacts, and the Iterator<String> is a perfect one.

You can easily convert your DAO to a ContactsDao or PeristentAddressBook that implement the AddressBook interface.

With the same idea of creating an interface you can create one to send the messages, on that will use a Gmail account and another to use an Outlook account (or anything else). And, why not, a generic one to send a message, whatever the protocol will be.

interface Sender {
  void send(String title, String message, String recipient)
}

Of course many lines of codes will be shared between the two email senders, you can have a look at the existing design patterns to share behaviors between classes. And will probably end with one abstract class that realize the template pattern :

abstract class SmtpSender implements Sender {
  abstract Session createSession();
  Message prepareMessage(Session session) {
    // ...
  }
  void send(String title, String message, String recipient) {
    Session session = createSession();
    Message message = prepareMessage();
    Transport.send(message);
  } 
}
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