1-way pager system design

The system design I implemented consists of several objects described below. Some parts have not been implemented yet.

system diagram

Main Servlet
This servlet starts the continuous loop that implements the various services provided by the system. When first invoked, the Main Servlet also initializes the User Data class that contains all user service configuration information. The Main Servlet will also provide the web pages that allow a user to configure their service parameters.
Loop
This class is a thread that constantly invokes the currently implemented services.
The Services
The only implemented service right now is the e-mail service. Each service, when launched by the Loop, reads in each user information from the User Data I/O class and decides if a page needs to be sent.
Page Sender
This class takes in parameters from a service and implements the sending of the message/page to the user's pager.
User Data I/O
What this does is allow the Main Servlet web pages to make additions and changes. It also provides requested information to the services. It has all user information saved to a file so that the system can persist after server downtime.