Fix issue in AnnotationMethodHandlerExceptionResolver

Caching of resovled exceptions introduced in SPR-7703 also introduced a
side effect whereby if exactly one exception was previously cached, any
other exception would appear as a match to the previously matched
@ExceptionHandler method.

This change ensures use of a fresh map when determining matching
@ExceptionHandler methods while also updating the cache.

Issue: SPR-9209

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/annotation/AnnotationMethodHandlerExceptionResolverTests.java

@@ -110,7 +110,7 @@ public class AnnotationMethodHandlerExceptionResolverTests {
 		assertEquals("Invalid view name returned", "GenericError", mav.getViewName());
 		assertEquals("Invalid status code returned", 500, response.getStatus());
 	}
-	
+
 	@Test(expected = IllegalStateException.class)
 	public void ambiguous() {
 		IllegalArgumentException ex = new IllegalArgumentException();
@@ -127,7 +127,7 @@ public class AnnotationMethodHandlerExceptionResolverTests {
 		assertTrue("ModelAndView not empty", mav.isEmpty());
 		assertEquals("Invalid response written", "IllegalArgumentException", response.getContentAsString());
 	}
-	
+
 	@Test
 	public void responseBody() throws UnsupportedEncodingException {
 		IllegalArgumentException ex = new IllegalArgumentException();
@@ -139,6 +139,20 @@ public class AnnotationMethodHandlerExceptionResolverTests {
 		assertEquals("Invalid response written", "IllegalArgumentException", response.getContentAsString());
 	}
 
+	// SPR-9209
+
+	@Test
+	public void cachingSideEffect() {
+		IllegalArgumentException ex = new IllegalArgumentException();
+		SimpleController controller = new SimpleController();
+
+		ModelAndView mav = exceptionResolver.resolveException(request, response, controller, ex);
+		assertNotNull("No ModelAndView returned", mav);
+
+		mav = exceptionResolver.resolveException(request, response, controller, new NullPointerException());
+		assertNull(mav);
+	}
+
 
 	@Controller
 	private static class SimpleController {