Use HttpHeaders.ALLOW instead of String constant

This commit changes "Allow" strings into HttpHeaders.ALLOW.

See gh-27356

spring-web/src/main/java/org/springframework/web/context/support/HttpRequestHandlerServlet.java

@@ -24,6 +24,7 @@
 import jakarta.servlet.http.HttpServletResponse;
 
 import org.springframework.context.i18n.LocaleContextHolder;
+import org.springframework.http.HttpHeaders;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
@@ -68,7 +69,7 @@ protected void service(HttpServletRequest request, HttpServletResponse response)
 		catch (HttpRequestMethodNotSupportedException ex) {
 			String[] supportedMethods = ex.getSupportedMethods();
 			if (supportedMethods != null) {
-				response.setHeader("Allow", StringUtils.arrayToDelimitedString(supportedMethods, ", "));
+				response.setHeader(HttpHeaders.ALLOW, StringUtils.arrayToDelimitedString(supportedMethods, ", "));
 			}
 			response.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, ex.getMessage());
 		}

spring-webmvc/src/main/java/org/springframework/web/servlet/FrameworkServlet.java

@@ -46,6 +46,7 @@
 import org.springframework.core.GenericTypeResolver;
 import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.lang.Nullable;
@@ -940,7 +941,7 @@ protected void doOptions(HttpServletRequest request, HttpServletResponse respons
 
 		if (this.dispatchOptionsRequest || CorsUtils.isPreFlightRequest(request)) {
 			processRequest(request, response);
-			if (response.containsHeader("Allow")) {
+			if (response.containsHeader(HttpHeaders.ALLOW)) {
 				// Proper OPTIONS response coming from a handler - we're done.
 				return;
 			}
@@ -950,7 +951,7 @@ protected void doOptions(HttpServletRequest request, HttpServletResponse respons
 		super.doOptions(request, new HttpServletResponseWrapper(response) {
 			@Override
 			public void setHeader(String name, String value) {
-				if ("Allow".equals(name)) {
+				if (HttpHeaders.ALLOW.equals(name)) {
 					value = (StringUtils.hasLength(value) ? value + ", " : "") + HttpMethod.PATCH.name();
 				}
 				super.setHeader(name, value);

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/AbstractController.java

@@ -20,6 +20,7 @@
 import jakarta.servlet.http.HttpServletResponse;
 import jakarta.servlet.http.HttpSession;
 
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.lang.Nullable;
 import org.springframework.web.servlet.ModelAndView;
@@ -155,7 +156,7 @@ public ModelAndView handleRequest(HttpServletRequest request, HttpServletRespons
 			throws Exception {
 
 		if (HttpMethod.OPTIONS.matches(request.getMethod())) {
-			response.setHeader("Allow", getAllowHeader());
+			response.setHeader(HttpHeaders.ALLOW, getAllowHeader());
 			return null;
 		}
 

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandler.java

@@ -560,7 +560,7 @@ public void handleRequest(HttpServletRequest request, HttpServletResponse respon
 		}
 
 		if (HttpMethod.OPTIONS.matches(request.getMethod())) {
-			response.setHeader("Allow", getAllowHeader());
+			response.setHeader(HttpHeaders.ALLOW, getAllowHeader());
 			return;
 		}