Getting NPE when using getServletConfig().getServletContext().getAttribute() (Java)

Question

I am using Servlets from not a long time. And i am getting this problem, which i can\'t terminate myself. I am using Servlets to create a small web project, and i tried to add m

Answer 1

Initialize your field in an overriden init(ServletConfig) method. The ServletConfig is not available at instance initialization time.

@Override
public void init(ServletConfig config) throws ServletException {
    super.init(config);
    this.clientService = config.getServletContext().getAttribute("clientService");
}

From the javadoc of Servlet#init(ServletConfig)

Called by the servlet container to indicate to a servlet that the servlet is being placed into service.

The servlet container calls the init method exactly once after instantiating the servlet. The init method must complete successfully before the servlet can receive any requests.

The javadoc of the GenericServlet implementation of init(ServletConfig) further specifies

This implementation stores the ServletConfig object it receives from the servlet container for later use. When overriding this form of the method, call super.init(config).