Reduce access on user in SimpleBrokerMessageHandler.handleMessageInternal

Issue: SPR-16264

spring-messaging/src/main/java/org/springframework/messaging/simp/broker/SimpleBrokerMessageHandler.java

@@ -260,7 +260,6 @@ public class SimpleBrokerMessageHandler extends AbstractBrokerMessageHandler {
 		SimpMessageType messageType = SimpMessageHeaderAccessor.getMessageType(headers);
 		String destination = SimpMessageHeaderAccessor.getDestination(headers);
 		String sessionId = SimpMessageHeaderAccessor.getSessionId(headers);
-		Principal user = SimpMessageHeaderAccessor.getUser(headers);
 
 		updateSessionReadTime(sessionId);
 
@@ -277,6 +276,7 @@ public class SimpleBrokerMessageHandler extends AbstractBrokerMessageHandler {
 			if (sessionId != null) {
 				long[] clientHeartbeat = SimpMessageHeaderAccessor.getHeartbeat(headers);
 				long[] serverHeartbeat = getHeartbeatValue();
+				Principal user = SimpMessageHeaderAccessor.getUser(headers);
 				this.sessions.put(sessionId, new SessionInfo(sessionId, user, clientHeartbeat, serverHeartbeat));
 				SimpMessageHeaderAccessor connectAck = SimpMessageHeaderAccessor.create(SimpMessageType.CONNECT_ACK);
 				initHeaders(connectAck);
@@ -293,6 +293,7 @@ public class SimpleBrokerMessageHandler extends AbstractBrokerMessageHandler {
 		else if (SimpMessageType.DISCONNECT.equals(messageType)) {
 			logMessage(message);
 			if (sessionId != null) {
+				Principal user = SimpMessageHeaderAccessor.getUser(headers);
 				handleDisconnect(sessionId, user, message);
 			}
 		}