spring-multi-tenancy
Utilizing the TargetSource and AOP infrastructure of Spring this enables for dynamic switching of basically anything. This has been used in production for switching SessionFactory's and/or DataSources based on some request parameter.
As of Hibernate 4.1 multi-tenant support is build into hibernate, this multi-tenant support also has been integrated into this. Finally we added also support for Spring Integration, there is a ChannelInterceptor which can be added to your channels to set/get the context from a message header.