Question

Creating servlet that implements contextInitializer interface in this code,

then accessing file inside contextinitialized() using this line

InputStream input = getServletContext().getResourceAsStream("/WEB-INF/file.properties"));

this exception occurred

java.lang.NullPointerException         at      
    javax.servlet.GenericServlet.getServletContext(GenericServlet.java:160)

any ideas ?

Answer 1

The ServletContextListener#contextInitialized() gives you the ServletContextEvent argument which provides you the getServletContext() method.

Thus, this should do:

public void contextInitialized(ServletContextEvent event) {
    InputStream input = event.getServletContext().getResourceAsStream("/WEB-INF/file.properties"));
    // ...
}

That said, you normally don’t want your servlet to implement this interface. The listener has a different purpose. Just override the HttpServlet#init() as follows:

protected void init() throws ServletException {
    InputStream input = getServletContext().getResourceAsStream("/WEB-INF/file.properties"));
    // ...
}