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

org.springframework.web.portlet/src/test/java/org/springframework/web/portlet/mvc/annotation/AnnotationMethodHandlerExceptionResolverTests.java

@@ -16,17 +16,20 @@
 
 package org.springframework.web.portlet.mvc.annotation;
 
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.net.BindException;
 import java.net.SocketException;
+
 import javax.portlet.PortletRequest;
 import javax.portlet.PortletResponse;
 
-import static org.junit.Assert.*;
 import org.junit.Before;
 import org.junit.Test;
-
 import org.springframework.mock.web.portlet.MockRenderRequest;
 import org.springframework.mock.web.portlet.MockRenderResponse;
 import org.springframework.stereotype.Controller;
@@ -106,6 +109,20 @@ public class AnnotationMethodHandlerExceptionResolverTests {
 		exceptionResolver.resolveException(request, response, controller, ex);
 	}
 
+	// 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 {