Simplify iteration over maps

Closes gh-23053

Author: stsypanov

spring-jms/src/main/java/org/springframework/jms/support/SimpleJmsHeaderMapper.java

@@ -92,10 +92,11 @@ public void fromHeaders(MessageHeaders headers, javax.jms.Message jmsMessage) {
 					logger.debug("Failed to set JMSType - skipping", ex);
 				}
 			}
-			Set<String> headerNames = headers.keySet();
-			for (String headerName : headerNames) {
+			Set<Map.Entry<String, Object>> entries = headers.entrySet();
+			for (Map.Entry<String, Object> entry : entries) {
+				String headerName = entry.getKey();
 				if (StringUtils.hasText(headerName) && !headerName.startsWith(JmsHeaders.PREFIX)) {
-					Object value = headers.get(headerName);
+					Object value = entry.getValue();
 					if (value != null && SUPPORTED_PROPERTY_TYPES.contains(value.getClass())) {
 						try {
 							String propertyName = this.fromHeaderName(headerName);

spring-test/src/main/java/org/springframework/test/context/cache/DefaultContextCache.java

@@ -180,9 +180,9 @@ public void remove(MergedContextConfiguration key, @Nullable HierarchyMode hiera
 		}
 
 		// Remove empty entries from the hierarchy map.
-		for (MergedContextConfiguration currentKey : this.hierarchyMap.keySet()) {
-			if (this.hierarchyMap.get(currentKey).isEmpty()) {
-				this.hierarchyMap.remove(currentKey);
+		for (Map.Entry<MergedContextConfiguration, Set<MergedContextConfiguration>> entry : this.hierarchyMap.entrySet()) {
+			if (entry.getValue().isEmpty()) {
+				this.hierarchyMap.remove(entry.getKey());
 			}
 		}
 	}

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/SessionAttributesHandler.java

@@ -113,8 +113,7 @@ public Map<String, Object> retrieveAttributes(WebSession session) {
 	 * @param attributes candidate attributes for session storage
 	 */
 	public void storeAttributes(WebSession session, Map<String, ?> attributes) {
-		attributes.keySet().forEach(name -> {
-			Object value = attributes.get(name);
+		attributes.forEach((name, value) -> {
 			if (value != null && isHandlerSessionAttribute(name, value.getClass())) {
 				session.getAttributes().put(name, value);
 			}