I have persistence.xml as below (just an example) and I want to retrieve set of all persistence-unit names. In this example a,b and c
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0">
<persistence-unit name="a">
</persistence-unit>
<persistence-unit name="b">
</persistence-unit>
<persistence-unit name="c">
</persistence-unit>
</persistence>