Connection pooling is done within the context of a J2EE Application server. Eclipse is an IDE, not an Application server. While it is possible to start and stop an Application server from within Eclipse and to deploy applications to a n Application Server, it is still the application server that is running your application and whatever connection pooling you're using, and not Eclipse.
My advice would be to search for this topic in your Application Server's documentation. The process for setting up a connection pool can vary significantly between Application Servers.