Allow Instant and ZonedDateTime as Last-Modified header.

Issues: SPR-17571

spring-web/src/main/java/org/springframework/http/HttpHeaders.java

@@ -1145,6 +1145,22 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 		setDate(LAST_MODIFIED, lastModified);
 	}
 
+	/**
+	 * Set the time the resource was last changed, as specified by the
+	 * {@code Last-Modified} header.
+	 */
+	public void setLastModified(Instant lastModified) {
+		setInstant(LAST_MODIFIED, lastModified);
+	}
+
+	/**
+	 * Set the time the resource was last changed, as specified by the
+	 * {@code Last-Modified} header.
+	 */
+	public void setLastModified(ZonedDateTime lastModified) {
+		setZonedDateTime(LAST_MODIFIED, lastModified);
+	}
+
 	/**
 	 * Return the time the resource was last changed, as specified by the
 	 * {@code Last-Modified} header.
@@ -1266,6 +1282,15 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 		set(headerName, DATE_FORMATTERS[0].format(date));
 	}
 
+	/**
+	 * Set the given date under the given header name after formatting it as a string
+	 * using the RFC-1123 date-time formatter. The equivalent of
+	 * {@link #set(String, String)} but for date headers.
+	 */
+	public void setInstant(String headerName, Instant date) {
+		setZonedDateTime(headerName, ZonedDateTime.ofInstant(date, GMT));
+	}
+
 	/**
 	 * Set the given date under the given header name after formatting it as a string
 	 * using the RFC-1123 date-time formatter. The equivalent of

spring-web/src/main/java/org/springframework/http/ResponseEntity.java

@@ -17,6 +17,8 @@
 package org.springframework.http;
 
 import java.net.URI;
+import java.time.Instant;
+import java.time.ZonedDateTime;
 import java.util.Arrays;
 import java.util.LinkedHashSet;
 import java.util.Optional;
@@ -359,6 +361,24 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 		 */
 		B lastModified(long lastModified);
 
+		/**
+		 * Set the time the resource was last changed, as specified by the
+		 * {@code Last-Modified} header.
+		 * @param lastModified the last modified date
+		 * @return this builder
+		 * @see HttpHeaders#setLastModified(long)
+		 */
+		B lastModified(ZonedDateTime lastModified);
+
+		/**
+		 * Set the time the resource was last changed, as specified by the
+		 * {@code Last-Modified} header.
+		 * @param lastModified the last modified date
+		 * @return this builder
+		 * @see HttpHeaders#setLastModified(long)
+		 */
+		B lastModified(Instant lastModified);
+
 		/**
 		 * Set the location of a resource, as specified by the {@code Location} header.
 		 * @param location the location
@@ -495,6 +515,18 @@ public class ResponseEntity<T> extends HttpEntity<T> {
 			return this;
 		}
 
+		@Override
+		public BodyBuilder lastModified(ZonedDateTime date) {
+			this.headers.setLastModified(date);
+			return this;
+		}
+
+		@Override
+		public BodyBuilder lastModified(Instant date) {
+			this.headers.setLastModified(date);
+			return this;
+		}
+
 		@Override
 		public BodyBuilder location(URI location) {
 			this.headers.setLocation(location);