Preferred way to handle Java exceptions in ServletContextListener

Question

For servlet lifecycle stuff, what do you guys recommend doing in response to an exception...

For example,

public class Foo implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent event) {
        try {
           // something nasty
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        try {
           // something nasty
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

I'm not entirely sure what will handle the runtime exception above. I'm working from the idea that if exceptions are thrown here, they're serious enough to break the system completely so an (unhandled) runtime exception may be ok.

I guess I'm asking what handles unchecked exceptions from servlet context listeners?

Answer 1

When you catch an exception, you might want to consider setting a ServletContext attribute to indicate that an error has been encountered. That way, if the container has not disabled the app, you can have Filters and/or Servlets inspect the ServletContext attribute and take appropriate action, like displaying an error page.

Answer 2

It seems that ServletContentListener is not designed to be able to exercise control over the lifecycle (otherwise it would be allowed to throw a ServletException).

As such, I would not rely on a RuntimeException to do anything useful. Looking at some other threads here, it seems to be logged and ignored on certain application servers.

If it is critical that the application does not start when your code fails, you should move that code into a Servlet's initialization section.

Answer 3

It is good tone to show some page like "Technical error, sorry" and not to show the stacktrace with the error message. Just log it and forward the user to error page.

Answer 4

We can the Exception through the object.printStackTrace(); or calling the Exception through out.print("Exception is"+ ex);