Adding a datasource to Tomcat and specifying it in persistence.xml

To add a datasource connecting to Oracle database, save the Oracle driver ojdbc7.jar into CATALINA_HOME/lib. Then add a line with the connection details into CATALINA_HOME/conf/context.xml:

<Resource name="jdbc/saphirOracleDB" auth="Container" type="javax.sql.DataSource"
        maxTotal="20" maxIdle="30" maxWait="10000"
        username="username" password="password" driverClassName="oracle.jdbc.OracleDriver"
        url="jdbc:oracle:thin:@//hostname:1555/servicename"/>

In a sample persistence.xml depending on the created datasource, the reference to the datasource is obtained using JNDI name java:/comp/env/jdbc/saphirOracleDB

<?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="Saphir" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <non-jta-data-source>java:/comp/env/jdbc/saphirOracleDB</non-jta-data-source>
    <class>entities.sqlresultmapping.DummyForMapping</class>
  </persistence-unit>
</persistence>

The entity manager can be obtained in the web application by using the specified persitence unit name:

    private static EntityManagerFactory emf = Persistence.createEntityManagerFactory("Saphir");
    private static EntityManager em = emf.createEntityManager();