Ensures that servlets handle only one request at a time. This interface has no methods.
If a servlet implements this interface, you areguaranteed that no two threads will execute concurrently in the servlet'sservice method. The servlet container can make this guarantee by synchronizing access to a single instance of the servlet, or by maintaining a pool of servlet instances and dispatching each new request to a free servlet.
This interface does not prevent synchronization problems that result from servlets accessing shared resources such as static class variables or classes outside the scope of the servlet.