Servlet init method having synchronized block

Question

I have one question. In my application, i have a servlet whose init code is as below.

public class GameInitServlet extends HttpServlet {

private static boolean initialized = false;

 @Override
    public void init() throws ServletException {
        // This is a safeguard against running init() more than once.
        synchronized (GameInitServlet.class) {
            if (initialized) {

                LOG.error("GameInitServlet has already been initialized... Bailing out!");
                return;
            }
            initialized = true;
        }
        //some code here....
    }
}

NOTE: In web.xml the above servlet is having load-on-startup as 1, so it will get initialized at the time of startup the app.

so my question is why we are synchronizing the init method. After all it will be taken care by servlet container and only get called once. Can i remove the above synchronization process or there will be some impact on the application after removing this.

Answer 1

init() will be executed only once when the Servlet is initially loaded into the container on its single instance which the Container will create. Then doGet() and doPost() methods will be executed for each request as separate threads of execution.I don't see any point of synchronizing init() method or any code inside it. Even in a distributed environment there may be one Servlet instance per JVM.I think the Container is wise enough to call init() only once in the Servlet's lifetime and hence there will not be any contention between multiple threads to execute init(). As per Javadocs,

The servlet container calls the init method exactly once after instantiating the servlet. The init method must complete successfully before the servlet can receive any requests.