The Entity API looks great and is very intuitive, but how does the server know which database is supposed to store/query the entity objects? The persistence.xml file, which will be placed under src/main/resources/META-INF of your project, is the standard JPA configuration file. By configuring this file, you can easily switch from one persistence provider to another and thus, also from one application server to another (believe it or not, this is a huge leap towards application server compatibility).

In the persistence.xml file, we will basically need to specify the persistence provider and the underlying data source used. Simply create the following file under src/main/resources/persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence 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...