Связь с postgresql в IDE

    public static void main(String[] args) throws SQLException {
        Class<Driver> driverClass = Driver.class;
        try (var connection = ConnectionManager.open()) {
            System.out.println(connection.getTransactionIsolation());
        }
    }
}

package jdbc.util;
 
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
 
public final class ConnectionManager {
 
    private static String PASSWORD_KEY = "db.password";
    private static String USERNAME_KEY = "db.username";
    private static String URL_KEY = "db.url";
 
    private ConnectionManager() {
    }
 
    public static Connection open() {
        try {
            return DriverManager.getConnection(
                PropertiesUtil.get(URL_KEY), 
                PropertiesUtil.get(USERNAME_KEY),
                PropertiesUtil.get(PASSWORD_KEY));
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
}

public final class PropertiesUtil {
    private static final Properties PROPERTIES = new Properties();
    static {
        loadProperties();
    }
    private PropertiesUtil() {
    }
    public static String get(String key) {
        return PROPERTIES.getProperty(key);
    }
    private static void loadProperties() {
        try (var inputStream = PropertiesUtil.class.getClassLoader().getResourceAsStream("/application.properties")) {
            PROPERTIES.load(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

var inputStream = PropertiesUtil.class.getClassLoader().getResourceAsStream("/application.properties")