Consistent and defensive Servlet 3.0 method calls across Spring's web abstraction

(in particular, also working in debug mode where method references may get resolved early, so ternary expressions are to be avoided)

Author: jhoeller

spring-web/src/main/java/org/springframework/http/server/ServletServerHttpResponse.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -39,6 +39,7 @@
  */
 public class ServletServerHttpResponse implements ServerHttpResponse {
 
+	/** Checking for Servlet 3.0+ HttpServletResponse.getHeader(String) */
 	private static final boolean servlet3Present =
 			ClassUtils.hasMethod(HttpServletResponse.class, "getHeader", String.class);
 
@@ -55,7 +56,7 @@ public class ServletServerHttpResponse implements ServerHttpResponse {
 	 * @param servletResponse the servlet response
 	 */
 	public ServletServerHttpResponse(HttpServletResponse servletResponse) {
-		Assert.notNull(servletResponse, "'servletResponse' must not be null");
+		Assert.notNull(servletResponse, "HttpServletResponse must not be null");
 		this.servletResponse = servletResponse;
 		this.headers = (servlet3Present ? new ServletResponseHttpHeaders() : new HttpHeaders());
 	}

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

@@ -57,7 +57,7 @@ public class ShallowEtagHeaderFilter extends OncePerRequestFilter {
 
 
 	/** Checking for Servlet 3.0+ HttpServletResponse.getHeader(String) */
-	private static final boolean responseGetHeaderAvailable =
+	private static final boolean servlet3Present =
 			ClassUtils.hasMethod(HttpServletResponse.class, "getHeader", String.class);
 
 
@@ -149,9 +149,11 @@ else if (isEligibleForEtag(request, responseWrapper, statusCode, body)) {
 	protected boolean isEligibleForEtag(HttpServletRequest request, HttpServletResponse response,
 			int responseStatusCode, byte[] responseBody) {
 
-		if (responseStatusCode >= 200 && responseStatusCode < 300 &&
-				HttpMethod.GET.name().equals(request.getMethod())) {
-			String cacheControl = (responseGetHeaderAvailable ? response.getHeader(HEADER_CACHE_CONTROL) : null);
+		if (responseStatusCode >= 200 && responseStatusCode < 300 && HttpMethod.GET.name().equals(request.getMethod())) {
+			String cacheControl = null;
+			if (servlet3Present) {
+				cacheControl = response.getHeader(HEADER_CACHE_CONTROL);
+			}
 			if (cacheControl == null || !cacheControl.contains(DIRECTIVE_NO_STORE)) {
 				return true;
 			}