Add addAll(MultiValueMap)

This commit introduces a new method for MultiValueMap: addAll, which
adds all values of a given map (cf putAll, which replaces existing
values).

Author: poutsma

spring-core/src/main/java/org/springframework/util/CollectionUtils.java

@@ -422,6 +422,13 @@ public void addAll(K key, List<? extends V> values) {
 			currentValues.addAll(values);
 		}
 
+		@Override
+		public void addAll(MultiValueMap<K, V> values) {
+			for (Entry<K, List<V>> entry : values.entrySet()) {
+				addAll(entry.getKey(), entry.getValue());
+			}
+		}
+
 		@Override
 		public void set(K key, V value) {
 			List<V> values = new LinkedList<>();

spring-core/src/main/java/org/springframework/util/LinkedMultiValueMap.java

@@ -93,6 +93,13 @@ public void addAll(K key, List<? extends V> values) {
 		currentValues.addAll(values);
 	}
 
+	@Override
+	public void addAll(MultiValueMap<K, V> values) {
+		for (Entry<K, List<V>> entry : values.entrySet()) {
+			addAll(entry.getKey(), entry.getValue());
+		}
+	}
+
 	@Override
 	public void set(K key, V value) {
 		List<V> values = new LinkedList<>();

spring-core/src/main/java/org/springframework/util/MultiValueMap.java

@@ -52,6 +52,13 @@ public interface MultiValueMap<K, V> extends Map<K, List<V>> {
 	 */
 	void addAll(K key, List<? extends V> values);
 
+	/**
+	 * Add all the values of the given {@code MultiValueMap} to the current values.
+	 * @param values the values to be added
+	 * @since 5.0
+	 */
+	void addAll(MultiValueMap<K, V> values);
+
 	/**
 	 * Set the given single value under the given key.
 	 * @param key the key

spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/StompHeaders.java

@@ -422,6 +422,13 @@ public void addAll(String headerName, List<? extends String> headerValues) {
 		currentValues.addAll(headerValues);
 	}
 
+	@Override
+	public void addAll(MultiValueMap<String, String> values) {
+		for (Entry<String, List<String>> entry : values.entrySet()) {
+			addAll(entry.getKey(), entry.getValue());
+		}
+	}
+
 	/**
 	 * Set the given, single header value under the given name.
 	 * @param headerName the header name

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

@@ -1357,6 +1357,13 @@ public void addAll(String key, List<? extends String> values) {
 		currentValues.addAll(values);
 	}
 
+	@Override
+	public void addAll(MultiValueMap<String, String> values) {
+		for (Entry<String, List<String>> entry : values.entrySet()) {
+			addAll(entry.getKey(), entry.getValue());
+		}
+	}
+
 	/**
 	 * Set the given, single header value under the given name.
 	 * @param headerName the header name