<?xml version="1.0" encoding="UTF-8"?>
<Context>
<WatchedResource>WEB-INF/web.xml</WatchedResource>
<WatchedResource>${catalina.base}/conf/web.xml</WatchedResource>
<!-- Deixa a conexão com o banco a cargo do container -->
<Resource name="jdbc/gymclub" auth="Container" type="javax.sql.DataSource"
           maxActive="100" maxIdle="30" maxWait="10000"
           username="admin" password="123456" driverclassname="org.postgresql.Driver"
           url="jdbc:postgresql://localhost:5432/gymclub"/>
</Context>

<resource-ref>
 <description>postgreSQL Datasource example</description>
 <res-ref-name>jdbc/gymclub</res-ref-name>
 <res-type>javax.sql.DataSource</res-type>
 <res-auth>Container</res-auth>
</resource-ref>

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1"
xmlns="http://xmlns.jcp.org/xml/ns/persistence"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
    <persistence-unit name="gymclub">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <!-- Deixa o controle de conexão com o banco a cargo do container. -->
    <non-jta-data-source>java:/comp/env/jdbc/gymclub</non-jta-data-source>
    <!-- Habilita cache de segundo nivel <shared-cache-mode>ENABLE_SELECTIVE</shared-cache-mode> -->
    <properties>
        <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQL9Dialect" />
        <!-- False no ambiente de produção -->
        <property name="hibernate.show_sql" value="true" />
        <property name="hibernate.format_sql" value="true" />
        <!-- None no ambiente de produção -->
        <property name="hibernate.hbm2ddl.auto" value="update" />
        <!-- Essa propriedade permite que as sequences sejam criadas com os valores
            iniciais que são especificados no domínio. -->
        <property name="hibernate.id.new_generator_mappings" value="true" />
        <!-- Cache de segundo nivel do hibernate <property name="hibernate.cache.region.factory_class"
            value="org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory" /> -->
    </properties>
</persistence-unit>

Cannot create JDBC driver of class '' for connect URL 'null'