Thread: Problems creating JApplet

Hello,

Finally I have a working Java Application containing 3 classes: Connection (Connectie), GUI (KretaGUI) and DatabaseActions (Kreta).

Everything works like a charm but now I have to make a JApplet. And that's where the trouble starts. I play around with it but I just can't get it to work. When I get some layoutstuff in the applet the .ini file can't be read (because an applet doesn't allow file operations).
This is driving me crazy. It's just part of an exercise that doesn't even get graded but I want to learn and understand how to make a JApplet.

This is the working code:

Connection class:

//Importeer bibliotheken
import java.io.FileInputStream;
import java.sql.*;
import java.util.Properties;
import javax.swing.JOptionPane;
// ****************************
 
public class Connectie {
	// Definieer private variabelen benodigd voor de connectie
	private String host;
	private String user;
	private String password;
	private String databasenaam;
 
	Connection connection;
 
	public void displaySQLErrors(Exception e) {
		String error;
		error = "SQL foutmelding: " + e.getMessage();
		JOptionPane.showMessageDialog(null, error,"foutmelding",JOptionPane.ERROR_MESSAGE);
	}
 
	public Connectie() {
		// Lees het config.ini bestand in
		this.LeesIniBestand();
 
		try {
			Class.forName("com.mysql.jdbc.Driver").newInstance();
			}
		catch(Exception e) {
			String error = "Niet mogelijk om de driver te laden";
			JOptionPane.showMessageDialog(null, error,"foutmelding",JOptionPane.ERROR_MESSAGE);
 
			System.exit(1);
		}
		try { // Bouw de connectiestring op
			connection = DriverManager.getConnection("jdbc:mysql://" + this.host + "/" + 
		this.databasenaam + "?user=" + this.user + "&password=" + this.password);
			//String succes = "Er is een connectie met de database";
			//JOptionPane.showMessageDialog(null, succes,"succes",JOptionPane.INFORMATION_MESSAGE);
		}
		catch(Exception e) {
			displaySQLErrors(e);
		}
	}
 
	public void LeesIniBestand() {
		try{
	      Properties p = new Properties();
	      p.load(new FileInputStream("config.ini")); //Het bestand config.ini staat in de root map van java
	      //Vul de database variabelen met de gegevens uit het .ini bestand
	      this.host = p.getProperty("host");
	      this.user = p.getProperty("user");
	      this.password = p.getProperty("password");
	      this.databasenaam = p.getProperty("databasenaam");
 
	      //Schrijf variabelen naar scherm ter controle
	      System.out.println("Host = " + p.getProperty("host"));
	      System.out.println("user = " + p.getProperty("user"));
	      System.out.println("Password = " + p.getProperty("password"));
	      System.out.println("databasenaam = " + p.getProperty("databasenaam"));
	      }
	    catch (Exception e) {
	      System.out.println(e);
	      }
	    }
}

GUI class:

//Importeer bibliotheken
import javax.swing.*;
import java.util.Vector;
import java.awt.*;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
// ************************************
 
public class KretaGUI {
	// In deze class wordt de GUI en alle events (JButton en JList) opgebouwd 
	JFrame frame;
	JButton bNieuw;
	JButton bToevoegen;
	JButton bBewerken;
	JButton bWis;
	JTextField tId;
	JTextField tNaam_gerecht;
	JTextField tPrijs;
	JTextArea tRecept;
	JTextArea tIngredienten;
	JLabel lId;
	JLabel lNaam_gerecht;
	JLabel lPrijs;
	JLabel lRecept;
	JLabel lIngredienten;
	JList gerechten;
 
	public KretaGUI(){
		Kreta kreta = new Kreta();
		Vector tabel;
		tabel = kreta.leesAlleGerechten();
 
		frame = new JFrame("Afhaalmenus");
		bNieuw = new JButton("Nieuw");
		bNieuw.addActionListener(new bNieuwListener());
		bToevoegen = new JButton("Toevoegen");
		bToevoegen.addActionListener(new bToevoegenListener());
		bBewerken = new JButton("Bewerken");
		bBewerken.addActionListener(new bBewerkenListener());
		bWis = new JButton("Wissen");
		bWis.addActionListener(new bWisListener());
		tId = new JTextField(3);
		tId.setEditable(false); // Het veld ID mag niet handmatig worden aangepast
		tNaam_gerecht = new JTextField(20);
		tPrijs = new JTextField(20);
		tRecept = new JTextArea(5,20);
		tIngredienten = new JTextArea(5,20);
		lId = new JLabel("Id:");
		lNaam_gerecht = new JLabel("Naam:");
		lPrijs = new JLabel("Prijs:");
		lRecept = new JLabel("Recept:");
		lIngredienten = new JLabel("Ingredienten:");
 
		JPanel panelA = new JPanel(new FlowLayout(FlowLayout.LEFT)); //Plaats de buttons boven in het frame links uitgelijnd
		JPanel panelB = new JPanel();  // Verzamel de textfields en textareas
		JPanel panelC = new JPanel(); //JList
		panelB.setLayout(new BoxLayout(panelB, BoxLayout.Y_AXIS)); //Plaats de labels en invoervelden onder elkaar
 
		// opmaak JTextArea
		JScrollPane sRecept = new JScrollPane(tRecept);
		tRecept.setLineWrap(true);
		sRecept.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
		sRecept.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
 
		JScrollPane sIngredienten = new JScrollPane(tIngredienten);
		tIngredienten.setLineWrap(true);
		sIngredienten.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
		sIngredienten.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
		// ***************************
 
		panelA.add(bNieuw);
		panelA.add(bToevoegen);
		panelA.add(bBewerken);
		panelA.add(bWis);
		panelB.add(lId);
		panelB.add(tId);
		panelB.add(lNaam_gerecht);
		panelB.add(tNaam_gerecht);
		panelB.add(lPrijs);
		panelB.add(tPrijs);
		panelB.add(lRecept);
		panelB.add(sRecept);
		panelB.add(lIngredienten);
		panelB.add(sIngredienten);
 
		gerechten = new JList(tabel);
		gerechten.addListSelectionListener(new LijstListener());
		gerechten.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); // Er kan maar 1 regel geselecteerd worden in de JList 
		gerechten.setSelectedIndex(-1); // Geen regel is geselecteerd
		panelC.add(gerechten);
 
		frame.getContentPane().add(BorderLayout.NORTH,panelA);
		frame.getContentPane().add(BorderLayout.WEST,panelB);
		frame.getContentPane().add(BorderLayout.EAST,panelC);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setSize(600,600);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
	}
 
 
	public static void main(String[] args) {
		KretaGUI afhaal = new KretaGUI();
	}
 
 
	class bNieuwListener implements ActionListener{
		// Maak alle velden leeg en verwijder de selectie van de JList als er op nieuw wordt geklikt.
		public void actionPerformed(ActionEvent event){
			gerechten.clearSelection(); // Zorg ervoor dat er geen recepten meer geselecteerd zijn 
			tId.setText("");
			tNaam_gerecht.setText("");
			tPrijs.setText("");
			tIngredienten.setText("");
			tRecept.setText("");
			tNaam_gerecht.requestFocus(); // Zet de focus in het veld naam
		}
	}
 
	class bBewerkenListener implements ActionListener{
		public void actionPerformed(ActionEvent event){
			int Geselecteerd;
			Geselecteerd = gerechten.getSelectedIndex(); // Bewaar de selectedindex van de JList
			Kreta kreta = new Kreta();
			kreta.setNaam_Gerecht(tNaam_gerecht.getText());
			kreta.setPrijs(tPrijs.getText());
			kreta.setIngredienten(tIngredienten.getText());
			kreta.setRecept(tRecept.getText());
			kreta.bewerkGerecht(Integer.parseInt(tId.getText()));
			gerechten.setListData(kreta.leesAlleGerechten());
			gerechten.repaint();
			gerechten.setSelectedIndex(Geselecteerd); // Selecteer de rij in de JList van het huidige record
		}
	}
 
	class bToevoegenListener implements ActionListener{
		// Voeg het nieuwe gerecht toe aan de database (insert)
		public void actionPerformed(ActionEvent event){
			Kreta kreta = new Kreta();
			kreta.setNaam_Gerecht(tNaam_gerecht.getText());
			kreta.setPrijs(tPrijs.getText());
			kreta.setIngredienten(tIngredienten.getText());
			kreta.setRecept(tRecept.getText());
			kreta.nieuwGerecht();
			// Toon nieuwe menu_id in JTextfield tId
			tId.setText(kreta.getId() + "");
			// Vul de JList gerechten met de nieuwe data
			gerechten.setListData(kreta.leesAlleGerechten());
			gerechten.repaint();
			// Indien het nieuwe record aan de tabel is toegevoegd dient de nieuwe regel in de JList geselecteerd te worden
			int lastIndex = gerechten.getModel().getSize() - 1;
			if (lastIndex >= 0) {
				gerechten.setSelectedIndex(lastIndex);
				}
		}
	}
 
	// Deze Klasse roept wisRecept aan 
	class bWisListener implements ActionListener{
		public void actionPerformed(ActionEvent event){
			Kreta kreta = new Kreta();
			kreta.wisGerecht(Integer.parseInt(tId.getText()));
			gerechten.setListData(kreta.leesAlleGerechten());
			gerechten.repaint();
			gerechten.clearSelection(); // Zorg ervoor dat er geen recepten meer geselecteerd zijn 
			tId.setText("");
			tNaam_gerecht.setText("");
			tPrijs.setText("");
			tIngredienten.setText("");
			tRecept.setText("");
			tNaam_gerecht.requestFocus(); // Zet de focus in het veld naam
			;
		}
	}
 
	class LijstListener implements ListSelectionListener
    {
        public void valueChanged(ListSelectionEvent e)
        {
            if (e.getValueIsAdjusting())
            {
            	Kreta kreta = new Kreta();
                try
                {
                    int menu_id = Integer.parseInt(((Vector)gerechten.getSelectedValue()).elementAt(0).toString());
                    kreta.leesGerecht(menu_id);
                    //tfdMenuID.setText(getmenu_id() + "");
                    tId.setText(kreta.getId() + "");
                    tNaam_gerecht.setText(kreta.getNaam_Gerecht());
                    tPrijs.setText(kreta.getPrijs());
                    tIngredienten.setText(kreta.getIngredienten());
                    tRecept.setText(kreta.getRecept());
                }
                catch(Exception ex)
                {
                    JOptionPane.showMessageDialog(null, ex.getMessage(), "Fout", JOptionPane.ERROR_MESSAGE);
                }
            }
         }
    }
}

Database stuff class:

//Importeer bibliotheken
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Vector;
import java.sql.*;
// *********************
 
public class Kreta {
	// In deze class worden de database bewerkingen uitgevoerd
	private Connectie con;
	private Vector vec;
	private int menu_id;
	private String naam_gerecht;
	private String prijs;
	private String ingredienten;
	private String recept;
 
	public void setId(int id){
		this.menu_id=menu_id;
	}
 
	public int getId(){
		return this.menu_id;
	}
 
	public void setNaam_Gerecht(String naam_gerecht){
		this.naam_gerecht=naam_gerecht;
	}
 
	public String getNaam_Gerecht(){
		return this.naam_gerecht;
	}
 
	public void setPrijs(String prijs){
		this.prijs=prijs;
	}
 
	public String getPrijs(){
		return this.prijs;
	}
 
	public void setIngredienten(String ingredienten){
		this.ingredienten=ingredienten;
	}
 
	public String getIngredienten(){
		return this.ingredienten;
	}
 
	public void setRecept(String recept){
		this.recept=recept;
	}
 
	public String getRecept(){
		return this.recept;
	}
 
	public Kreta(){
		con = new Connectie();
		vec = new Vector();
	}
 
	public Kreta(int menu_id,String naam_gerecht,String prijs,String ingredienten,String recept){
		this();
		this.menu_id = menu_id;
		this.naam_gerecht = naam_gerecht;
		this.prijs = prijs;
		this.ingredienten = ingredienten;
		this.recept = recept;
	}
 
	public Vector leesAlleGerechten(){
		// Maak een vector die alle records uit de tabel afhaalmenus ophaalt.
		try {
			Statement statement = con.connection.createStatement();
			String gget;
			gget = "SELECT DISTINCT menu_id,naam_gerecht,prijs FROM afhaalmenus;";
 
			ResultSet rs = statement.executeQuery(gget);
 
			while (rs.next()){
				Vector vRow = new Vector<>();
				for(int x = 1;x <=3;x++){
					vRow.addElement(rs.getString(x));
				}
				vec.add(vRow);
			}
		} catch (Exception e) {
			con.displaySQLErrors(e);
		}
		return vec;
	}
 
public void leesGerecht(int id){
	// Lees een record met het meegegeven id uit de tabel afhaalmenus
		try{
			PreparedStatement sset = con.connection.prepareStatement("SELECT DISTINCT * FROM afhaalmenus WHERE menu_id = ? ");
			sset.setInt(1, id);			//Eerste parameter '?' is het menu_id welke wordt toegekend in het eerste stuk van de functie. 
 
			ResultSet rs = sset.executeQuery();
			rs.next();
			this.menu_id = rs.getInt(1);
			this.naam_gerecht = rs.getString(2);
			this.prijs = rs.getString(3);
			this.ingredienten = rs.getString(4);
			this.recept = rs.getString(5);
		}catch(Exception e){
			e.printStackTrace(); // Ik maak gebruik van de printstack om meer informatie te verkrijgen bij een exception
		}
	}
 
public void wisGerecht(int id){
	// Delete het record met het menu_id id uit de tabel afhaalmenus
	try {
		PreparedStatement sset = con.connection.prepareStatement("DELETE FROM afhaalmenus WHERE menu_id = ?");
		sset.setInt(1, id);			//Eerste parameter '?' is het menu_id welke wordt toegekend in het eerste stuk van de functie. 
		sset.executeUpdate();
		}
	catch (Exception e){
		e.printStackTrace(); // Ik maak gebruik van de printstack om meer informatie te verkrijgen bij een exception
		}
	}
 
public void nieuwGerecht(){
	try {
		// Insert statement opbouwen
		// Ik maak gebruik van een prepared statement omdat dit veel overzichtelijker werkt
		// Met Statement.RETURN_GENERATED_KEYS krijg ik de nieuw aangemaakte menu_id terug
		PreparedStatement sset = con.connection.prepareStatement("INSERT INTO afhaalmenus (naam_gerecht,prijs,ingredienten,recept) VALUES (?,?,?,?)",Statement.RETURN_GENERATED_KEYS);
		sset.setString(1, this.naam_gerecht);	//Eerste parameter '?' is het naam_gerecht
		sset.setString(2, this.prijs);			//Tweede parameter '?' is het prijs
		sset.setString(3, this.ingredienten);	//Derde parameter '?' is het ingredienten
		sset.setString(4, this.recept);			//Vierde parameter '?' is het recept
		sset.executeUpdate();
		ResultSet tableKeys = sset.getGeneratedKeys();
		tableKeys.next();
		this.menu_id = tableKeys.getInt(1);
		}
	catch (Exception e){
		e.printStackTrace(); // Ik maak gebruik van de printstack om meer informatie te verkrijgen bij een exception 
		}
	}
 
public void bewerkGerecht(int id) {
	// Update het geselecteerde record in de tabel afhaalmenus
    try
    {
    	PreparedStatement sset = con.connection.prepareStatement("UPDATE afhaalmenus SET naam_gerecht = ?,prijs = ?,ingredienten = ?,recept = ? " +
    			"WHERE menu_id = ?");
		sset.setString(1, this.naam_gerecht);	
		sset.setString(2, this.prijs);			
		sset.setString(3, this.ingredienten);	
		sset.setString(4, this.recept);	
		sset.setInt(5, id);
		sset.executeUpdate();
    }
    catch(Exception e) 	{
    e.printStackTrace(); // Ik maak gebruik van de printstack om meer informatie te verkrijgen bij een exception
    }
    }
}

I would be very gratefull if you guys could show me how to make a JApplet out of this.

Thanks in advance!!!

This is a crosspost to Problems creating JApplet

To simplify this part of the exercise (and all future programs you might write), it's important to separate the GUI logic from the business logic. Your business/data/GUI logic is currently very intertwined. I tried to create a simple example of what to do using your code, but separating the GUI from the rest of the rat's nest was more than I was willing to take on. Once this separation exists, coding the option to show it in a JApplet would be as simple as adding the following code:

public class GUIToApplet extends JApplet
{
    public void init()
    {  
        KretaGUI content = new KretaGUI();
        setContentPane(content);
    }
 
} // end class GUIToApplet

and running it as a JApplet or showing it in a web page. In order for the above code to work, KretaGUI would have to be a java.awt.Container, but that's easily accomplished.

I don't know how much time you have, but to understand better the 'separation' idea I've proposed, you should study the Model-View-Controller design pattern or architecture.

This ungraded exercise is forcing you to think in that direction, and that's a good thing, but it would have been nice if they'd have helped you down that path a bit by giving you some design guidelines before you started coding. Shaping what you have now into separable classes will take some time and might be a frustrating activity. But then, what else do you have to do?

Originally Posted by GregBrannon

To simplify this part of the exercise (and all future programs you might write), it's important to separate the GUI logic from the business logic. Your business/data/GUI logic is currently very intertwined. I tried to create a simple example of what to do using your code, but separating the GUI from the rest of the rat's nest was more than I was willing to take on. Once this separation exists, coding the option to show it in a JApplet would be as simple as adding the following code:

public class GUIToApplet extends JApplet
{
    public void init()
    {  
        KretaGUI content = new KretaGUI();
        setContentPane(content);
    }
 
} // end class GUIToApplet

and running it as a JApplet or showing it in a web page. In order for the above code to work, KretaGUI would have to be a java.awt.Container, but that's easily accomplished.

I don't know how much time you have, but to understand better the 'separation' idea I've proposed, you should study the Model-View-Controller design pattern or architecture.

This ungraded exercise is forcing you to think in that direction, and that's a good thing, but it would have been nice if they'd have helped you down that path a bit by giving you some design guidelines before you started coding. Shaping what you have now into separable classes will take some time and might be a frustrating activity. But then, what else do you have to do?

Dear GregBrannon.... Thank you very much for your very detailed and helpfull information.
This thing is just killing me.

I really thought that I separated all of the gui stuff in the KretaGUI class. Apparently not. The thing that bugs me is that I created this application and it does what it needs to do. EXCEPT the applet stuff.

But I quess I have to start from scratch.
I will look at the information you supplied.

Thanks again for taking your time in helping me!

--- Update ---

Originally Posted by andbin

First, use of JDBC in applets is more critical and requires some considerations about security and permissions. Please, read for example:
Essentials, Part 1, Lesson 7: Database Access and Permissions

Second:
new FileInputStream("config.ini")

This is a file specification on the local file-system. And more important, it's relative to the current directory. What is the directory that is "current" when the JVM, activated by browser, is launched to execute the applet? You don't know for sure ......
And apart this, an applet can come from an host on internet .... why the applet should expect to find that configuration file on the machine of the user?

I guess you don't know some basics about applets, so, please understand these things before continue!

Dear andbin: Thank you for your help. I will look into this later.

GregBrannon: Could you please give me a little push in helping me to devide the code in business/data/GUI.
Because I just don't see it.

Thanks in advance!

--- Update ---

Finally...I have got my applet working...The only thing that doesnt work is reading the .ini file (java.io.FileNotFoundException: config.ini (The system cant find the file))

However its part of the assignment to read the database settings from an .ini file.

I hope I can finally complete mt assignement.