How can I set values in persistence.xml?

Question

I have tried to load the url, user and password in different ways, but I can't get it to connect.

Currently I use a file called config.properties from where I retrieve the credentials to connect to the database.

Persistence file

<persistence xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             version="2.2"
             xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd">

    <persistence-unit name="tienda" transaction-type="RESOURCE_LOCAL">
        <class>com.chisrra.tienda.entities.Producto</class><!--opcional-->

        <properties>
            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>

            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
            <!-- Cargamos las propiedades de la base de datos desde el archivo database.properties -->
            <property name="javax.persistence.jdbc.url" value="${tienda.db.url}"/>
            <property name="javax.persistence.jdbc.user" value="${tienda.db.user}"/>
            <property name="javax.persistence.jdbc.password" value="${tienda.db.password}"/>
        </properties>
    </persistence-unit>
</persistence>

Class where I retrieve properties

public class JPAUtils {
    private static final EntityManagerFactory FACTORY = Persistence.createEntityManagerFactory("tienda");

    static {
        Properties properties = new Properties();
        String path = "src/config.properties";
        try (InputStream inputStream = new FileInputStream(path)) {
            properties.load(inputStream);
            String url = properties.getProperty("tienda.db.url");
            String user = properties.getProperty("tienda.db.user");
            String password = properties.getProperty("tienda.db.password");

        } catch (FileNotFoundException e) {
            throw new RuntimeException("No se encontro el archivo config.properties: " + e.getMessage(),e);
        } catch (IOException e) {
            throw new RuntimeException("No se pudieron cargar las propiedades del archivo config.properties: " + e.getMessage(),e);
        }
    }

    private static Properties createProperties(String url, String user, String password) {
        Properties properties = new Properties();
        properties.setProperty("javax.persistence.jdbc.url", url);
        properties.setProperty("javax.persistence.jdbc.user", user);
        properties.setProperty("javax.persistence.jdbc.password", password);
        return properties;
    }

    public static EntityManager getentityManager() {
        return FACTORY.createEntityManager();
    }
}