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servlet-filterstomcat8

How can I programatically obtain a servlet filter instance?

I have a class MyFilter which implements javax.servlet.Filter. Tomcat creates a single instance of this based on the web.xml configuration. The filter collects statistics about all requests (since application start) and stores them in member variables.

I wish to display these statistics on a web page. How can I obtain the instance of MyFilter which was created by Tomcat?

Solution

  • Quoting from the documentation:

    Every Filter has access to a FilterConfig object from which it can obtain its initialization parameters, a reference to the ServletContext which it can use.

    Why do not you store the data you need in ServletContext attributes? You can store the filter as follows:

    @Override
public void init(FilterConfig config) throws ServletException
{
    // Store our instance in the servlet context for usage by servlets.
    ServletContext context = config.getServletContext();
    context.setAttribute("MyFilter", this);
}

    And then in the servlet with the same context:

    Filter filter = (Filter) getServletContext().getAttribute("MyFilter");