Mocking private field in servlet filter

Question

Is is possible to mock (currently using Mockito, may be also other testing lib) the field 'sf' in the class shown below:

public class SomeFilter implements Filter {

   private Logger log = Logger.getLogger(getClass());
   private SomeField sf = new SomeField();

   @Override
   public void init(FilterConfig fc) throws ServletException {
      log.info("");
   }

   @Override
   public void doFilter(ServletRequest req, ServletResponse res, FilterChain fc) throws     IOException, ServletException {
        fc.doFilter(request, response);
   }

   @Override
   public void destroy() {
      log.info("");
   }
}

If so, how?

Answer 1

Consider PowerMock framework with some nifty features, including some integration with Mockito framework

Consider this example to bypass encapsulation and access private field, like below

String sf = Whitebox.getInternalState(o, "sf", String.class, B.class);
Whitebox.setInternalState(o, "sf", "XXX", B.class);

Also consider (from the last link):

All of these things can be achieved without using PowerMock, this is just normal Java reflection. However reflection requires much boiler-plate code and can be error prone and thus PowerMock provides you with these utility methods instead. PowerMock gives you a choice on whether to refactor your code and add getter/setter methods for checking/altering internal state or whether to use its utility methods to accomplish the same thing without changing the production code. It's up to you!