Disable response caching when controller resolves ETag

See gh-22797

Author: rstoyanchev

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -48,6 +48,7 @@
 import org.springframework.web.bind.support.WebDataBinderFactory;
 import org.springframework.web.context.request.NativeWebRequest;
 import org.springframework.web.context.request.ServletWebRequest;
+import org.springframework.web.filter.ShallowEtagHeaderFilter;
 import org.springframework.web.method.support.ModelAndViewContainer;
 import org.springframework.web.servlet.mvc.support.RedirectAttributes;
 import org.springframework.web.servlet.support.RequestContextUtils;
@@ -207,6 +208,7 @@ public void handleReturnValue(@Nullable Object returnValue, MethodParameter retu
 						&& isResourceNotModified(inputMessage, outputMessage)) {
 					// Ensure headers are flushed, no body should be written.
 					outputMessage.flush();
+					ShallowEtagHeaderFilter.disableContentCaching(inputMessage.getServletRequest());
 					// Skip call to converters, as they may update the body.
 					return;
 				}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -21,6 +21,7 @@
 import java.lang.reflect.Method;
 import java.lang.reflect.Type;
 import java.util.concurrent.Callable;
+import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
 import org.springframework.core.MethodParameter;
@@ -33,6 +34,7 @@
 import org.springframework.web.bind.annotation.ResponseBody;
 import org.springframework.web.bind.annotation.ResponseStatus;
 import org.springframework.web.context.request.ServletWebRequest;
+import org.springframework.web.filter.ShallowEtagHeaderFilter;
 import org.springframework.web.method.HandlerMethod;
 import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
 import org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite;
@@ -104,6 +106,7 @@ public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer
 
 		if (returnValue == null) {
 			if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
+				disableContentCachingIfNecessary(webRequest);
 				mavContainer.setRequestHandled(true);
 				return;
 			}
@@ -160,6 +163,18 @@ private boolean isRequestNotModified(ServletWebRequest webRequest) {
 		return webRequest.isNotModified();
 	}
 
+	private void disableContentCachingIfNecessary(ServletWebRequest webRequest) {
+		if (!isRequestNotModified(webRequest)) {
+			HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);
+			Assert.notNull(response, "Expected HttpServletResponse");
+			if (StringUtils.hasText(response.getHeader("ETag"))) {
+				HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
+				Assert.notNull(request, "Expected HttpServletRequest");
+				ShallowEtagHeaderFilter.disableContentCaching(request);
+			}
+		}
+	}
+
 	private String formatErrorForReturnValue(@Nullable Object returnValue) {
 		return "Error handling return value=[" + returnValue + "]" +
 				(returnValue != null ? ", type=" + returnValue.getClass().getName() : "") +