Работал ли с DBMS

try (Connection conn = DriverManager.getConnection(
        "jdbc:postgresql://localhost:5432/mydb", "user", "pass")) {
    Statement stmt = conn.createStatement();
    ResultSet rs = stmt.executeQuery("SELECT * FROM users");
    while (rs.next()) {
        System.out.println(rs.getString("username"));
    }
} catch (SQLException e) {
    e.printStackTrace();
}