Load On Start Up using Annotation in JAVA

Question

I have this code,

@WebServlet(value="/initializeResources", loadOnStartup=1)
public class InitializeResources extends HttpServlet {

  @Override
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
          throws ServletException, IOException {
      System.out.println("HEREEEE");
  }

}

But the servlet doesn't start when the web application is started.

How use load on startup on Servlet Annotation?

My Servlet API is 3.0 and I use Tomcat 7

Answer 1

With you current code, you need to do a GET request for see the output HEREEEE.

If you want to do something on the startup of the servlet (i.e. the element loadOnStartup with value greater or equal to zero, 0), you need put the code in a init method or in the constructor of the servlet:

@Override
public void init() throws ServletException {
    System.out.println("HEREEEE");
}

---

It may be more convenient to use a listener to start a resource in the application scope (in the ServletContext).

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

@WebListener
public class InitializeListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("On start web app");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("On shutdown web app");
    }

}

For an example, see my answer for the question Share variables between JAX-RS requests.