Polish ExceptionHandlerMethodResolver mapping

See gh-27801

Author: Adam Ostrožlík

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ExceptionHandlerExceptionResolver.java

@@ -476,11 +476,7 @@ protected ServletInvocableHandlerMethod getExceptionHandlerMethod(
 			// Local exception handler methods on the controller class itself.
 			// To be invoked through the proxy, even in case of an interface-based proxy.
 			handlerType = handlerMethod.getBeanType();
-			ExceptionHandlerMethodResolver resolver = this.exceptionHandlerCache.get(handlerType);
-			if (resolver == null) {
-				resolver = new ExceptionHandlerMethodResolver(handlerType);
-				this.exceptionHandlerCache.put(handlerType, resolver);
-			}
+			ExceptionHandlerMethodResolver resolver = this.exceptionHandlerCache.computeIfAbsent(handlerType, ExceptionHandlerMethodResolver::new);
 			Method method = resolver.resolveMethod(exception);
 			if (method != null) {
 				return new ServletInvocableHandlerMethod(handlerMethod.getBean(), method, this.applicationContext);