Add support for setting the "Vary" response header

Issue: SPR-14070

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

@@ -19,7 +19,10 @@ package org.springframework.web.servlet.mvc.method.annotation;
 import java.io.IOException;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
+import java.util.Map;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ResolvableType;
@@ -40,6 +43,8 @@ import org.springframework.web.bind.support.WebDataBinderFactory;
 import org.springframework.web.context.request.NativeWebRequest;
 import org.springframework.web.method.support.ModelAndViewContainer;
 
+import static org.springframework.http.HttpHeaders.VARY;
+
 /**
  * Resolves {@link HttpEntity} and {@link RequestEntity} method argument values
  * and also handles {@link HttpEntity} and {@link ResponseEntity} return values.
@@ -162,9 +167,18 @@ public class HttpEntityMethodProcessor extends AbstractMessageConverterMethodPro
 		Assert.isInstanceOf(HttpEntity.class, returnValue);
 		HttpEntity<?> responseEntity = (HttpEntity<?>) returnValue;
 
+		HttpHeaders outputHeaders = outputMessage.getHeaders();
 		HttpHeaders entityHeaders = responseEntity.getHeaders();
+		if (outputHeaders.containsKey(VARY) && entityHeaders.containsKey(VARY)) {
+			List<String> values = getVaryRequestHeadersToAdd(outputHeaders, entityHeaders);
+			if (!values.isEmpty()) {
+				outputHeaders.setVary(values);
+			}
+		}
 		if (!entityHeaders.isEmpty()) {
-			outputMessage.getHeaders().putAll(entityHeaders);
+			for (Map.Entry<String, List<String>> entry : entityHeaders.entrySet()) {
+				outputHeaders.putIfAbsent(entry.getKey(), entry.getValue());
+			}
 		}
 
 		Object body = responseEntity.getBody();
@@ -188,6 +202,27 @@ public class HttpEntityMethodProcessor extends AbstractMessageConverterMethodPro
 		outputMessage.flush();
 	}
 
+	private List<String> getVaryRequestHeadersToAdd(HttpHeaders responseHeaders, HttpHeaders entityHeaders) {
+		if (!responseHeaders.containsKey(HttpHeaders.VARY)) {
+			return entityHeaders.getVary();
+		}
+		List<String> entityHeadersVary = entityHeaders.getVary();
+		List<String> result = new ArrayList<String>(entityHeadersVary);
+		for (String header : responseHeaders.get(HttpHeaders.VARY)) {
+			for (String existing : StringUtils.tokenizeToStringArray(header, ",")) {
+				if ("*".equals(existing)) {
+					return Collections.emptyList();
+				}
+				for (String value : entityHeadersVary) {
+					if (value.equalsIgnoreCase(existing)) {
+						result.remove(value);
+					}
+				}
+			}
+		}
+		return result;
+	}
+
 	private boolean isResourceNotModified(ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage) {
 		List<String> ifNoneMatch = inputMessage.getHeaders().getIfNoneMatch();
 		long ifModifiedSince = inputMessage.getHeaders().getIfModifiedSince();

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

@@ -19,6 +19,7 @@ package org.springframework.web.servlet.support;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
@@ -27,7 +28,9 @@ import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
 import org.springframework.http.CacheControl;
+import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.web.HttpRequestMethodNotSupportedException;
@@ -77,6 +80,10 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 
 	protected static final String HEADER_CACHE_CONTROL = "Cache-Control";
 
+	/** Checking for Servlet 3.0+ HttpServletResponse.getHeaders(String) */
+	private static final boolean servlet3Present =
+			ClassUtils.hasMethod(HttpServletResponse.class, "getHeaders", String.class);
+
 
 	/** Set of supported HTTP methods */
 	private Set<String> supportedMethods;
@@ -89,6 +96,11 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 
 	private int cacheSeconds = -1;
 
+	private String[] varyByRequestHeaders;
+
+
+	// deprecated fields
+
 	/** Use HTTP 1.0 expires header? */
 	private boolean useExpiresHeader = false;
 
@@ -245,6 +257,29 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 		return this.cacheSeconds;
 	}
 
+	/**
+	 * Configure one or more request header names (e.g. "Accept-Language") to
+	 * add to the "Vary" response header to inform clients that the response is
+	 * subject to content negotiation and variances based on the value of the
+	 * given request headers. The configured request header names are added only
+	 * if not already present in the response "Vary" header.
+	 *
+	 * <p><strong>Note:</strong> this property is only supported on Servlet 3.0+
+	 * which allows checking existing response header values.
+	 * @param varyByRequestHeaders one or more request header names
+	 * @since 4.3
+	 */
+	public void setVaryByRequestHeaders(String... varyByRequestHeaders) {
+		this.varyByRequestHeaders = varyByRequestHeaders;
+	}
+
+	/**
+	 * Return the configured request header names for the "Vary" response header.
+	 */
+	public String[] getVaryByRequestHeaders() {
+		return this.varyByRequestHeaders;
+	}
+
 	/**
 	 * Set whether to use the HTTP 1.0 expires header. Default is "false",
 	 * as of 4.2.
@@ -363,6 +398,11 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 		else {
 			applyCacheSeconds(response, this.cacheSeconds);
 		}
+		if (servlet3Present && this.varyByRequestHeaders != null) {
+			for (String value : getVaryRequestHeadersToAdd(response)) {
+				response.addHeader("Vary", value);
+			}
+		}
 	}
 
 	/**
@@ -546,4 +586,25 @@ public abstract class WebContentGenerator extends WebApplicationObjectSupport {
 		}
 	}
 
+	private Collection<String> getVaryRequestHeadersToAdd(HttpServletResponse response) {
+		if (!response.containsHeader(HttpHeaders.VARY)) {
+			return Arrays.asList(getVaryByRequestHeaders());
+		}
+		Collection<String> result = new ArrayList<String>(getVaryByRequestHeaders().length);
+		Collections.addAll(result, getVaryByRequestHeaders());
+		for (String header : response.getHeaders(HttpHeaders.VARY)) {
+			for (String existing : StringUtils.tokenizeToStringArray(header, ",")) {
+				if ("*".equals(existing)) {
+					return Collections.emptyList();
+				}
+				for (String value : getVaryByRequestHeaders()) {
+					if (value.equalsIgnoreCase(existing)) {
+						result.remove(value);
+					}
+				}
+			}
+		}
+		return result;
+	}
+
 }