jdbc.driverClassName = com.mysql.jdbc.Driver
jdbc.url = jdbc:mysql://localhost:3306/testdb
jdbc.username = root
jdbc.password =

//Default Constructor
public DBManagerImpl(){
    JDBC_DRIVER = getResource().getProperty("jdbc.driverClassName","com.mysql.jdbc.Driver");
    try {
        Class.forName(JDBC_DRIVER);
    }...
}

//Getting properties file
private Properties getResource(){
    Properties prop = new Properties();
    InputStream input = null;
    try {
        input = getClass().getClassLoader().getResourceAsStream("config.properties");
        prop.load(input);
    } ...
    return prop;
}

public Connection getConnection() {
    Connection connection = null;
    try {
        DATABASE_URL = getResource().getProperty("jdbc.url", "jdbc:mysql://localhost:3306/defaultdb");
        username = getResource().getProperty("jdbc.username", "root");
        password = getResource().getProperty("jdbc.password", "");
        connection = DriverManager.getConnection(DATABASE_URL, username, password);
    } ...
    return connection;
}