Database Connection design question

Question

Hello, I have a design question. Awhile back I needed to create a database connection to SQL Server, so I created a class to do it
import java.sql.*;
import java.io.*;
import java.net.MalformedURLException;
import org.w3c.dom.Document;
import org.w3c.dom.*;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
public class SQLServerConnection
     private static Connection connection = null;
     public SQLServerConnection(String user, String password, String dbName) throws java.sql.SQLException
          getDBConnection(user, password, dbName);
     public SQLServerConnection(String configFileName) throws java.sql.SQLException
          getDBConnection(configFileName);
     private void getDBConnection(String user, String password, String dbName) throws java.sql.SQLException
         DriverManager.registerDriver(new com.microsoft.jdbc.sqlserver.SQLServerDriver());
         connection = DriverManager.getConnection(
              "jdbc:microsoft:sqlserver:" + dbName, user, password);              
     private void getDBConnection(String configFileName) throws java.sql.SQLException
          String user;
          String password;
          String dbName;
          try
               DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
               DocumentBuilder db = factory.newDocumentBuilder();
               Document doc = db.parse(configFileName);
               doc.getDocumentElement().normalize();
               // get the configuration information
               password = getConfigParameter("password", doc);
               user = getConfigParameter("username", doc);
               dbName = getConfigParameter("databasename", doc);
               getDBConnection(user, password, dbName);
          catch (MalformedURLException murle)
               System.out.println("Unable to connect to: " + configFileName + " -- " + murle);
               System.exit(1);
          catch (FileNotFoundException fnfe)
               System.out.println("Configuration file " + configFileName + " not found.");
               System.exit(1);
          catch (IOException ioe)
               System.out.println("IOException: " + ioe);
               System.exit(1);
          catch (javax.xml.parsers.ParserConfigurationException pce)
               System.out.println ("Parser Configuration Error: " + pce);
          catch (SAXException saxe)
               System.out.println ("SAXException: " + saxe);
     private String getConfigParameter(String paramName, org.w3c.dom.Document doc)
          NodeList nl = doc.getElementsByTagName(paramName);
          if(nl != null)
               Node n = null;
               for (int i = 0; i < nl.getLength(); i++)
                    n = nl.item(i);          
                    if(n.hasChildNodes())
                         NodeList children = n.getChildNodes();
                         return ((Node)children.item(0)).getNodeValue();
          else
               System.out.println ("nl is null");
          return "";          
     public void setCatalog(String catalogName) throws java.sql.SQLException
          connection.setCatalog(catalogName);
     public Connection getConnection()
          return connection;
     public void closeConnection()
          try
               connection.close();
          catch(java.sql.SQLException sqle)
               System.err.println ("SQL Server Connection failed to close: " + sqle);
}Later on, I needed to do the same thing for MySQL, so I created a class for that, MySQLServerConnection which is exactly the same as above, except for:
private void getDBConnection(String user, String password, String dbName) throws java.sql.SQLException
          try
               Class.forName("com.mysql.jdbc.Driver").newInstance();
               connection = DriverManager.getConnection(dbName, user, password);     
          catch(java.lang.ClassNotFoundException cnfe)
               System.out.println (cnfe);
          catch(java.lang.InstantiationException ie)
               System.out.println (ie);
          catch(java.lang.IllegalAccessException iae)
               System.out.println (iae);
     }Later, on, I did the same thing with OracleServerConnection. My question is, I know this is probably not optimal code. For example, I didn't originally have a close connection method, so I had to go in and code one for all 3. I'm assuming that an interface would be a good idea so that if I have to code another database connection class I make sure and include all of the appropriate methods. I'm also assuming that it would have been smart to have a master class, maybe something like DatabaseConnection and extended these classes from that. Am I on the right track? Totally offbase?

Answer 1

@nclow - I will work on trying the Factory Pattern for this over the weekend and post when I finish to see what you think.
@abillconsl - just to make sure I understand, you're saying that I just try to connect and it will cycle through the different database connection possibilities and connect when it finds the right one? If it fails all 3, log an appropriate message. One question I have about this is, I thought I was being object oriented by separating the different types of db connections (Oracle, SQL Server, MySql) into different classes. Am I missing the point of OOP by what I was/am trying to accomplish? Going overboard? Also, does your way try and connect to all 3 even if I connected to one already?
Thx, Grantarchy
Edited by: grantarchy on May 9, 2008 9:50 PM