Testing Annotation based RequestInterceptor

I wanted to do so custom logic(Record the request and response) on some routes. Based on some research I came decided to use AnnotationBased RequestInterceptor. This is my code for interceptor.

public class CustomInterceptor extends HandlerInterceptorAdapter {
@Override
public void afterCompletion(final HttpServletRequest request,
                            final HttpServletResponse response,
                            final Object handler,
                            final Exception ex) {
     if (handler != null && handler instanceof  HandlerMethod) {
        HandlerMethod handlerMethod = (HandlerMethod) handler;
        CustomRecord annotation = AnnotationUtils.getAnnotation(handlerMethod.getMethod(), CustomRecord.class);
        if (annotation != null) {
              // Record Request and Response in a File.
        }
}

Now this class is working as expected but I was unable to unit test this function.

• I first thought of trying a creating an HandlerMethod Object but I did not get anywhere.

• Second I tried to use PowerMokito. This was my test code:

  @RunWith(PowerMockRunner.class)
  @PrepareForTest(CustomInterceptor.class)
  @PowerMockIgnore("javax.management.*")
  public class CustomInterceptorTest {
  @Test
  public void restAnnotationRecording_negetivecase() {
    HandlerMethod mockHandler = mock(HandlerMethod.class);
    PowerMockito.mockStatic(AnnotationUtils.class);
    when(AnnotationUtils.getAnnotation(mockHandler.getMethod(), 
         CustomRecord.class).thenReturn(null);
    // Verify file is not saved
  }
   // A spy is stubbed using when(spy.foo()).then() syntax. It is safer to stub spies - - with doReturn|Throw() family of methods. More in javadocs for Mockito.spy() methodcannot be saved.
  @Test
  public void restAnnotationRecording_happycase() {
      HandlerMethod mockHandler = mock(HandlerMethod.class);
      PowerMockito.mockStatic(AnnotationUtils.class);
      when(AnnotationUtils.getAnnotation(mockHandler.getMethod(), CustomRecord.class).thenReturn(mockAnnotation);
      // Verify file is saved
  }
  }
  
  

  • This gives an Error A spy is stubbed using when(spy.foo()).then() syntax. It is safer to stub spies with doReturn|Throw() family of methods.

I wanted to check if there is any method to test the Interceptor. I am a newbie in Java, thanks for help.