Threads, concurrency, or synchronization are not very easy to understand concepts. When some concurrency is involved in our applications it’s pretty hard to avoid making mistakes. Although Java provides mechanisms to deal with parallel programming, sometimes there are just too many options. And often some essential options are missing. For web applications, Jakarta EE provides a simplified programming model to deal with parallel tasks. But in order to use it effectively and avoid mistakes, you need to understand the basic concepts which I’d like to explain here.