How to add a datasource in wildfly swarm with .war packaging?

In the simple case where you can simply use the default data source in your persistence unit, you can just specify the connection details using the following Java system properties:

swarm.ds.name           - Name of the datasource (e.g. ExampleDS)   
swarm.ds.username       - Username to access the database   
swarm.ds.password       - Password to access the database   
swarm.ds.connection.url - URL connection to use

Setting these values configures the JTA data source, so you can have a very basic persistence.xml:

<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0">
  <persistence-unit name="example">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <class>entity.user</class>
    <properties>
      <property name="hibernate.hbm2ddl.auto" value="create" />
      <property name="hibernate.show_sql" value="true"/>
    </properties>
  </persistence-unit>
</persistence>

The datasource name doesn’t seem to matter.

For (slightly) more information, see https://wildfly-swarm.gitbooks.io/wildfly-swarm-users-guide/content/configuration_properties.html