The name of the default factory changed between Tomcat 7 and Tomcat 8. A couple of attribute names also changed. This is all as a result of switching from DBCP 1.x to DBCP 2.x in Tomcat 8. You want the following in your META-INF/context.xml file:
<!-- PostgreSQL Datasource -->
<Resource auth="Container"
driverClassName="org.postgresql.Driver"
factory="org.apache.tomcat.dbcp.dbcp2.BasicDataSourceFactory"
maxTotal="50"
maxIdle="10"
maxWaitMillis="-1"
name="jdbc/mydb"
type="javax.sql.DataSource"
url="jdbc:postgresql://myorg.corp.net:5432/mydb"
username="abc"
password="def" />
Since this factory is used by default for resources of type javax.sql.DataSource
you can just drop that attribute all together. The other changes were:
maxActive -> maxTotal
maxWait -> maxWaitMillis