This little POC implements a multiple Datasources sample using AbstractRoutingDataSource.
This sample uses Tomcat JDBC as connection pool and works with Spring transactions using @Transactional.
Feel free to improve this project.
Javadoc for AbstractRoutingDataSource: http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/jdbc/datasource/lookup/AbstractRoutingDataSource.html