[FIXED] Creating a servlet in Vaadin with Spring Boot to add session listeners

Issue

I am trying to create a servlet in Vaadin 14 running on Spring boot. I have read the Application lifecycle page on Vaadin Application lifecycle and have tried creating a servlet with the help of that but have not succeeded. My webpage doesn't seem to recognize the URL. I have tried both VaadinServlet and SpringServlet, here is my code:

@WebServlet(value = "name", urlPatterns = {"customservlet"})
public class CustomServlet extends SpringServlet implements SessionInitListener, SessionDestroyListener {

    public CustomServlet(ApplicationContext context, boolean forwardingEnforced) {
        super(context, forwardingEnforced);
    }

    @Override
    protected void servletInitialized() throws ServletException {
        super.servletInitialized();
        getService().addSessionInitListener(this);
        getService().addSessionDestroyListener(this);
    }

    @Override
    public void sessionInit(SessionInitEvent event)
            throws ServiceException {
        // Do session start stuff here
    }

    @Override
    public void sessionDestroy(SessionDestroyEvent event) {
        // Do session end stuff here
    }


    @Override
    protected void service(HttpServletRequest request,
                           HttpServletResponse response) throws ServletException, IOException {

        getService().addSessionInitListener((SessionInitListener) event -> event.getSession().addRequestHandler(globalRequestHandler()));
        super.service(request, response);
    }

    public RequestHandler globalRequestHandler() {
        return (session, vaadinRequest, response) -> {
            if ("/customservlet".equals(vaadinRequest.getPathInfo())) {
                response.setContentType("text/html;charset=UTF-8");
                response.getWriter().append("some content");
                response.getWriter().flush();
                return true;
            } else  {
                return false;
            }
        };
    }
}

Edit: It worked with Leifs with solution. Here are the results if anyone wants to know:

@Route("yourroute")
@SpringComponent
public class MyInitListener implements Serializable, VaadinServiceInitListener  {

    @Override
    public void serviceInit(ServiceInitEvent serviceEvent) {
        serviceEvent.getSource().addSessionInitListener(initEvent -> {
            initEvent.getSession().addRequestHandler(globalRequestHandler());

        });
        serviceEvent.getSource(). addSessionDestroyListener(initEvent -> {
            initEvent.getSession().close();
        });
    }

public RequestHandler globalRequestHandler() {
        return (session, vaadinRequest, response) -> {
            if ("/yourroute".equals(vaadinRequest.getPathInfo())) {
                response.setContentType("text/plain");
                PrintWriter pw = response.getWriter();
                pw.write("Some content");
                pw.close();
                return true;
            } else  {
                return false;
            }
        };
    }
}

Solution

I will try to give an answer to the thing you seem to want to achieve (adding session listeners) rather than the way you try to do that (creating a custom servlet).

The easiest way to add those listeners is with a VaadinServiceInitListener. When using Spring, you can do that just by defining a bean that implements that interface.

@Component
public class MyInitListener implements VaadinServiceInitListener {
  @Override
  public void serviceInit(ServiceInitEvent serviceEvent) {
    serviceEvent.getSource().addSessionInitListener(initEvent -> {
      // Do session start stuff here      
    });
    serviceEvent.getSource(). addSessionDestroyListener(initEvent -> {
      // Do session end stuff here      
    });
  }
}

Answered By - Leif Åstrand
Answer Checked By - Robin (JavaFixing Admin)