How do I create a database class for an application 1

[TheFitz]

Hi All,

I'm sure I'm asking the most basic of questions, so sorry if this seems to be the very basics. I am trying my best to learn Java....

I have an access database which for example is called "myDB.mdb".

I can access this database from a class that I have written to output a simple select to the console.

To my understanding, in a larger application I should place database connections into a separate class so I can reference this class to access the database.

I have spent a few days on Google trying to understand how to do this, but all it shows me is how to create the simple connection I have already done.

Am I looking at this in the right way??

Can anyone give me some code to both a) setup the class file and b) an example of how to reference it from a different class.

I have tried to do the following, but it doesn't work properly, so this could be a starting point:

getConnection.java

package Database;

import java.sql.Array;
import java.sql.Blob;
import java.sql.CallableStatement;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.NClob;
import java.sql.PreparedStatement;
import java.sql.SQLClientInfoException;
import java.sql.SQLException;
import java.sql.SQLWarning;
import java.sql.SQLXML;
import java.sql.Savepoint;
import java.sql.Statement;
import java.sql.Struct;
import java.util.Map;
import java.util.Properties;

public abstract class getConnection implements Connection {
	
	public static Connection getConnection() throws Exception {
	    String driver = "sun.jdbc.odbc.JdbcOdbcDriver";
	    //String url = "jdbc:odbc:northwind";
	    String url = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ=C:\\myDB.mdb;}";
	    String username = "admin";
	    String password = "";
	    Class.forName(driver);
	    return DriverManager.getConnection(url, username, password);
	}

}

frmLogon.java

package Forms;

import java.awt.EventQueue;


public class frmLogon {

	private JFrame frmLogon;
	private JTextField txtUserID;
	private JPasswordField txtPassword;
	
	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					frmLogon window = new frmLogon();
					window.frmLogon.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

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

	/**
	 * Initialize the contents of the frame.
	 */
	private void initialize() {
		frmLogon = new JFrame();
		frmLogon.setTitle("Logon");
		frmLogon.setBounds(100, 100, 253, 171);
		frmLogon.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frmLogon.getContentPane().setLayout(null);
		
		txtUserID = new JTextField();
		txtUserID.setBounds(77, 11, 152, 20);
		frmLogon.getContentPane().add(txtUserID);
		txtUserID.setColumns(10);
		
		txtPassword = new JPasswordField();
		txtPassword.setBounds(77, 42, 152, 20);
		frmLogon.getContentPane().add(txtPassword);
		
		JLabel lblUserId = new JLabel("User ID:");
		lblUserId.setBounds(10, 14, 57, 14);
		frmLogon.getContentPane().add(lblUserId);
		
		JLabel lblPassword = new JLabel("Password:");
		lblPassword.setBounds(10, 42, 57, 14);
		frmLogon.getContentPane().add(lblPassword);

		final JLabel lblError = new JLabel(" ");
		lblError.setHorizontalAlignment(SwingConstants.CENTER);
		lblError.setForeground(Color.RED);
		lblError.setBounds(10, 73, 219, 14);
		frmLogon.getContentPane().add(lblError);
		
		JButton btnLogon = new JButton("Logon");
		btnLogon.addMouseListener(new MouseAdapter() {
			@Override
			
			public void mouseClicked(MouseEvent arg0) {
				
			char[] strPassword = txtPassword.getPassword();
				
			if(txtUserID.getText().equals("")||txtUserID.getText().equals(null))
				{
					System.out.println("No User ID");
					lblError.setText("Please Enter A User ID");
					return;
				}
			else
				{
					if(strPassword.length==0)
						{
							System.out.println("No Password");
							lblError.setText("Please Enter A Password");
							return;
						}
					else
						{
							/*if(new String (txtPassword.getPassword()).equals("MyPassword"))
							{
								System.out.println("This is the value: xx" + txtUserID.getText() + "xx");
								System.out.println("System Logon");
								lblError.setText("  ");
							}
							else
							{
								System.out.println("This is the value: xx" + txtUserID.getText() + "xx");
								lblError.setText("Invalid Password");
								return;
							} */
						}
				}
			
			/// Insert DB Try Here
			System.out.println( "Path is " + System.getProperty("java.class.path()"));
		    
			Connection conn = getConnection();
		    Statement st = conn.createStatement();

		    ResultSet rs = st.executeQuery("SELECT * FROM tblUsers");

		    ResultSetMetaData rsMetaData = rs.getMetaData();

		    int numberOfColumns = rsMetaData.getColumnCount();
		    System.out.println("resultSet MetaData column Count=" + numberOfColumns);

		    st.close();
		    conn.close();
			}


		});
		
		btnLogon.setBounds(20, 98, 89, 23);
		frmLogon.getContentPane().add(btnLogon);
		
		JButton btnQuit = new JButton("Quit");
		btnQuit.addMouseListener(new MouseAdapter() {
			@Override
			public void mouseClicked(MouseEvent arg0) {
				System.exit(0);
			}
		});
		btnQuit.setBounds(119, 98, 89, 23);
		frmLogon.getContentPane().add(btnQuit);

	}
}

Many thanks for any help you can give me,

Regards,

Fitz

Fitz
Did you know, there are 10 types of people in this world:
* Those who understand binary
and
* Those who Don't!!

 

[Diancecht]

First of all, by convention class names start with capital letter and you should use a name like ConnectionManager instead of getConnection for your database class


Well, in your case, instead of

Connection conn = getConnection();

a simple

Connection conn = getConnection.getConnection();

You will also need an

import Database.getConnection;

sentence.

Meanwhile, this may help you to understand method calls

Cheers,
Dian

 

[TheFitz]

Hi Dian,

That's bang on!!! I now know a little more. It's slowly stating to make sense, but more importantly, I understand how to use a common class. . . .

I am now sorting out the class names as suggested. I did know about naming conventions, however, I think I may have been a little confused when I started putting it together.

I've jsut had a little test of it and it seems to be working within the expected results, which admittedly isn't a lot!!

Thanks so much for your help,

Regards,

Fitz

Fitz
Did you know, there are 10 types of people in this world:
* Those who understand binary
and
* Those who Don't!!