Question

Consider the following class: import java.sql. ; public class ConnDBServer / public Connection con; public ConnDBServer() { try class.ForName("com.mysql.jdbc.Driver"); String url - ".jdbc.mysql://localhost:3306/db1"; con - DriverManager.getConnection(url, "root", "root"); catch (ClassNotFoundException e) { e.printStackTrace(); catch (SOLException e) { e.printStackTrace(); LaSalle College 2020-05-01 (v. 1.7) colo 22005010. 1.7 It is used to create a connection to the MySQL database db1. For example: import java.sql.* ; public class Main public static void main(String[] args) { Connection con- new ConnDBServer().con; Make the necessary changes in the Conn DBServer class to ensure that in the application we will always use the same connection, that we will not have more than one connection to the database. Ensure as well that the connection will be created only when it is actually needed for the first time. Show how in the main function we will call this connection.

Answer 1

//ConnDBServer class

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.SQLException;

import java.sql.ResultSet;

import java.sql.Statement;

public class ConnDBServer {

    private static String url = "jdbc:mysql://localhost:3306/prototypeeop";    

    private static String driverName = "com.mysql.jdbc.Driver";   

    private static String username = "root";   

    private static String password = "root";

    private static Connection con;

    private static String urlstring;

    public static Connection getConnection() {

        try {

            Class.forName(driverName);

            try {

                con = DriverManager.getConnection(urlstring, username, password);

            } catch (SQLException ex) {

                // log an exception. fro example:

                System.out.println("Failed to create the database connection.");

            }

        } catch (ClassNotFoundException ex) {

            // log an exception. for example:

            System.out.println("Driver not found.");

        }

        return con;

    }

}

//Main class

import java.sql.*;

public class Main {

    public static void main (String[] args) {

        Connection con = null;

        Statement stmt = null;

        ResultSet rs = null;

        String sql="";

        try {

            con = ConnDBServer.getConnection();

            stmt = con.createStatement();

            rs = stmt.executeQuery(sql);

        }catch(Exception ex) {

                System.out.println("Main.");

        }

    }

}