Update async dispatch check in OncePerRequestFilter

We no longer need to rely on an indirect check since Servlet 3.0 is expected
so we can just check the DispatcherType of the request.

Closes gh-26282

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/filter/OncePerRequestFilter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -145,7 +145,7 @@ private boolean skipDispatch(HttpServletRequest request) {
 	 * @see WebAsyncManager#hasConcurrentResult()
 	 */
 	protected boolean isAsyncDispatch(HttpServletRequest request) {
-		return WebAsyncUtils.getAsyncManager(request).hasConcurrentResult();
+		return request.getDispatcherType().equals(DispatcherType.ASYNC);
 	}
 
 	/**

spring-web/src/test/java/org/springframework/web/filter/CharacterEncodingFilterTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@
 
 package org.springframework.web.filter;
 
+import javax.servlet.DispatcherType;
 import javax.servlet.FilterChain;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
@@ -51,6 +52,7 @@ public void forceEncodingAlwaysSetsEncoding() throws Exception {
 		request.setCharacterEncoding(ENCODING);
 		given(request.getAttribute(WebUtils.ERROR_REQUEST_URI_ATTRIBUTE)).willReturn(null);
 		given(request.getAttribute(filteredName(FILTER_NAME))).willReturn(null);
+		given(request.getDispatcherType()).willReturn(DispatcherType.REQUEST);
 
 		HttpServletResponse response = mock(HttpServletResponse.class);
 		FilterChain filterChain = mock(FilterChain.class);
@@ -71,6 +73,7 @@ public void encodingIfEmptyAndNotForced() throws Exception {
 		given(request.getCharacterEncoding()).willReturn(null);
 		given(request.getAttribute(WebUtils.ERROR_REQUEST_URI_ATTRIBUTE)).willReturn(null);
 		given(request.getAttribute(filteredName(FILTER_NAME))).willReturn(null);
+		given(request.getDispatcherType()).willReturn(DispatcherType.REQUEST);
 
 		MockHttpServletResponse response = new MockHttpServletResponse();
 
@@ -92,6 +95,7 @@ public void doesNotIfEncodingIsNotEmptyAndNotForced() throws Exception {
 		given(request.getCharacterEncoding()).willReturn(ENCODING);
 		given(request.getAttribute(WebUtils.ERROR_REQUEST_URI_ATTRIBUTE)).willReturn(null);
 		given(request.getAttribute(filteredName(FILTER_NAME))).willReturn(null);
+		given(request.getDispatcherType()).willReturn(DispatcherType.REQUEST);
 
 		MockHttpServletResponse response = new MockHttpServletResponse();
 
@@ -112,6 +116,7 @@ public void withBeanInitialization() throws Exception {
 		given(request.getCharacterEncoding()).willReturn(null);
 		given(request.getAttribute(WebUtils.ERROR_REQUEST_URI_ATTRIBUTE)).willReturn(null);
 		given(request.getAttribute(filteredName(FILTER_NAME))).willReturn(null);
+		given(request.getDispatcherType()).willReturn(DispatcherType.REQUEST);
 
 		MockHttpServletResponse response = new MockHttpServletResponse();
 
@@ -135,6 +140,7 @@ public void withIncompleteInitialization() throws Exception {
 		given(request.getCharacterEncoding()).willReturn(null);
 		given(request.getAttribute(WebUtils.ERROR_REQUEST_URI_ATTRIBUTE)).willReturn(null);
 		given(request.getAttribute(filteredName(CharacterEncodingFilter.class.getName()))).willReturn(null);
+		given(request.getDispatcherType()).willReturn(DispatcherType.REQUEST);
 
 		MockHttpServletResponse response = new MockHttpServletResponse();
 
@@ -156,6 +162,7 @@ public void setForceEncodingOnRequestOnly() throws Exception {
 		request.setCharacterEncoding(ENCODING);
 		given(request.getAttribute(WebUtils.ERROR_REQUEST_URI_ATTRIBUTE)).willReturn(null);
 		given(request.getAttribute(filteredName(FILTER_NAME))).willReturn(null);
+		given(request.getDispatcherType()).willReturn(DispatcherType.REQUEST);
 
 		HttpServletResponse response = mock(HttpServletResponse.class);
 		FilterChain filterChain = mock(FilterChain.class);