Another feature:
instead of of server.xml, you can add "Resource" tag in
your_application/META-INF/Context.xml
(according to tomcat docs)
like this:
<Context>
<Resource name="jdbc/DatabaseName" auth="Container" type="javax.sql.DataSource"
username="dbUsername" password="dbPasswd"
url="jdbc:postgresql://localhost/dbname"
driverClassName="org.postgresql.Driver"
initialSize="5" maxWait="5000"
maxActive="120" maxIdle="5"
validationQuery="select 1"
poolPreparedStatements="true"/>
</Context>