You Need to create a Connection pool and then associate that connection pool with a JNDI resource on glassfish such as the following(these entries are from domain.xml):
<jdbc-resource enabled="true" jndi-name="jdbc/mysql" object-type="user" pool-name="mysqlpool"/>
<jdbc-connection-pool allow-non-component-callers="false" associate-with-thread="false" connection-creation-retry-attempts="0" connection-creation-retry-interval-in-seconds="10" connection-leak-reclaim="false" connection-leak-timeout-in-seconds="0" connection-validation-method="auto-commit" datasource-classname="com.mysql.jdbc.jdbc2.optional.MysqlDataSource" fail-all-connections="false" idle-timeout-in-seconds="300" is-connection-validation-required="false" is-isolation-level-guaranteed="false" lazy-connection-association="false" lazy-connection-enlistment="false" match-connections="false" max-connection-usage-count="0" max-pool-size="32" max-wait-time-in-millis="60000" name="mysqlpool" non-transactional-connections="false" pool-resize-quantity="2" res-type="javax.sql.DataSource" statement-timeout-in-seconds="-1" steady-pool-size="8" validate-atmost-once-period-in-seconds="0" wrap-jdbc-objects="false">
<property name="DatabaseName" value="mydb"/>
<property name="password" value="shhh"/>
<property name="user" value="foouser"/>
<property name="port" value="3306"/>
<property name="ServerName" value="foo.com"/>
</jdbc-connection-pool>
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