10.8. Summary

In this chapter, we've built an interactive messenger service. In doing so, we've had a chance to use most of the techniques and patterns we've been gathering throughout this book.

In the course of developing the messenger, we've made use of the entire JavaSpaces API (from read to notify to snapshot). Our application makes use of advanced techniques we've encountered in recent chapters as well. We've put distributed events to use by reading channel messages reactively (through the use of the notify method). We've used leasing on our session entries to ensure that they won't persist long after their corresponding users have logged out of the messenger service. Finally, we've made use of transactions, to make sure our application is robust in the distributed environment, even in the face of partial failure.

Of course, a commercial version of a messenger service would deliver additional features (some of which you'll add through the exercises that follow). But our focus wasn't on bells and whistles: we've concentrated on building a correct and robust application. You can use all the techniques we tied together in the messenger service as a springboard to building other robust distributed applications.