Question

I need to release some resources in my web application (Tomcat 7).
I try to do it in the destroy of my servlet.
The problem is that when I do getServletContext() in my destroy nothing happens.
By debugging I managed to see:

java.lang.NullPointerException
at javax.servlet.GenericServlet.getServletContext(GenericServlet.java:125)

Originating from my line getSerlvetContext() in the destroy method of my servlet.

So right now, I have no idea how am I supposed to do clean up in my web application.
I have stored some resources in the ServletContext so that it can be used from anywhere in my application and as far as I know
the resource clean-up should be done either

1) in the destroy of servlets or
2) the contextDestroyed of an ServletContextListener

But neither of these seem to work properly. In case (1) I get the NullPointerException when trying to access servlet context.
In case (2) the web application is already shutdown so if I have static methods responsible to do e.g. reallocation of DB connections etc the classes (as I have understood the problem) have already been unloaded by the JVM since the web app has been already shutdown.

Am I doing something wrong? What should I be doing?

Answer 1

To get the ServletContext, the usual way is to store it in an instance variable. Depending on whether you extend Servlet or implement a ServletContextListener, I would recommend to create an instance variable for the context and then store it from one of these methods:

• ServletContextListener.contextInitialized(ServletContextEvent sce): Use sce.getServletContext() to obtain a reference of the context, which you can then store in an instance variable.
• HttpServlet.init(ServletConfig config): Call the super method (init) with the config param, so you can later access it using getServletContext(). If that doesn’t work, you can store the context in an instance variable using config.getServletContext().