Merge branch '5.1.x'

spring-web/src/main/java/org/springframework/http/ReadOnlyHttpHeaders.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.
@@ -40,10 +40,15 @@ class ReadOnlyHttpHeaders extends HttpHeaders {
 	@Nullable
 	private MediaType cachedContentType;
 
+	@Nullable
+	private List<MediaType> cachedAccept;
+
+
 	ReadOnlyHttpHeaders(HttpHeaders headers) {
 		super(headers.headers);
 	}
 
+
 	@Override
 	public MediaType getContentType() {
 		if (this.cachedContentType != null) {
@@ -56,6 +61,18 @@ class ReadOnlyHttpHeaders extends HttpHeaders {
 		}
 	}
 
+	@Override
+	public List<MediaType> getAccept() {
+		if (this.cachedAccept != null) {
+			return this.cachedAccept;
+		}
+		else {
+			List<MediaType> accept = super.getAccept();
+			this.cachedAccept = accept;
+			return accept;
+		}
+	}
+
 	@Override
 	public List<String> get(Object key) {
 		List<String> values = this.headers.get(key);