CODEWITHSUNDEEP
javaservletsinit
Ritesh Kaushik
Ritesh Kaushik

Reputation: 735

Java Servlets Overriding init(ServletConfig config)

I am trying to override init(ServletConfig config) method.My code is:

 public void init(ServletConfig config) throws ServletException {
    ServletContext sc = getServletContext(); // ----- NullPointerException
}

this is giving NullPointerException .

If i modify it as:

   public void init(ServletConfig config) throws ServletException {
    ServletContext sc = config.getServletContext(); // ----- works fine
}

This works fine. I know that we should override init() method and not init(ServletConfig config) but
Can anybody give me proper reason as why this is happening?

Upvotes: 8

Views: 28581

Answers (4)

Jay Jain
Jay Jain

Reputation: 73

Just put the super init(config) at very first line of your overridden method 

public void init(ServletConfig config) throws ServletException

Upvotes: 0

Bhavik Ambani
Bhavik Ambani

Reputation: 6657

This happens because you are overriding wrong method mechanism If you overriding

     public void init(ServletConfig config) throws ServletException {
        super.init(config);
            ServletContext sc = getServletContext(); 
     }

Instead of overriding init(ServletConfig), simply override the below method and it will be called by GenericServlet.init(ServletConfig config)

 public void init() throws ServletException {
 ServletContext sc = getServletContext(); 
}

Upvotes: 2

bhuang3
bhuang3

Reputation: 3633

Because in :

public void init(ServletConfig config) throws ServletException
{
    ServletContext sc = getServletContext();
}

you don't invoke super.init(ServletConfig). As a result, ServletConfig is not stored in the servlet instance, and subsequent calls to getServletConfig will return null.

Upvotes: 1

Perception
Perception

Reputation: 80593

Compare the documentation for init(ServletConfig):

public void init(ServletConfig config)throws ServletException
Called by the servlet container to indicate to a servlet that the servlet
is being placed into service.

See Servlet#init. 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).

And compare that with the documentation for init():

public void init() throws ServletException
A convenience method which can be overridden so that there's no need to
call super.init(config).

Instead of overriding init(ServletConfig), simply override this method
and it will be called by GenericServlet.init(ServletConfig config). The
ServletConfig object can still be retrieved via getServletConfig().

When overriding init(ServletConfig), the first thing that must be done is to call:

super.init(config);

If you do this then calling directly to getServletContext() in your method will no longer result in an NPE.

Upvotes: 20

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