Apply SingleSpaceSeparator Checkstyle module

This commit also fixes its violations.

Closes gh-31469

spring-messaging/src/main/java/org/springframework/messaging/rsocket/annotation/support/RSocketFrameTypeMessageCondition.java

@@ -143,7 +143,7 @@ public class RSocketFrameTypeMessageCondition extends AbstractMessageCondition<R
 				}
 			}
 		}
-		return  null;
+		return null;
 	}
 
 	@Override

spring-messaging/src/main/java/org/springframework/messaging/rsocket/service/RSocketRequestValues.java

@@ -59,7 +59,7 @@ public final class RSocketRequestValues {
 
 
 	public RSocketRequestValues(
-			@Nullable String route, @Nullable List<Object> routeVariables,  @Nullable MetadataHelper metadataHelper,
+			@Nullable String route, @Nullable List<Object> routeVariables, @Nullable MetadataHelper metadataHelper,
 			@Nullable Object payloadValue, @Nullable Publisher<?> payload,
 			@Nullable ParameterizedTypeReference<?> payloadElementType) {
 

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

@@ -492,7 +492,7 @@ public class DefaultStompSession implements ConnectionHandlingStompSession {
 		TcpConnection<byte[]> con = this.connection;
 		Assert.state(con != null, "No TcpConnection available");
 		if (connect[0] > 0 && connected[1] > 0) {
-			long interval = Math.max(connect[0],  connected[1]);
+			long interval = Math.max(connect[0], connected[1]);
 			con.onWriteInactivity(new WriteInactivityTask(), interval);
 		}
 		if (connect[1] > 0 && connected[0] > 0) {

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

@@ -43,7 +43,7 @@ import org.springframework.util.Assert;
  * @since 4.0
  * @see StompDecoder
  */
-public class StompEncoder  {
+public class StompEncoder {
 
 	private static final Byte LINE_FEED_BYTE = '\n';
 

spring-messaging/src/main/java/org/springframework/messaging/simp/user/MultiServerUserRegistry.java

@@ -183,7 +183,7 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 
 	@Override
 	public String toString() {
-		return "local=[" + this.localRegistry +	"], remote=" + this.remoteRegistries;
+		return "local=[" + this.localRegistry + "], remote=" + this.remoteRegistries;
 	}
 
 

spring-messaging/src/main/java/org/springframework/messaging/support/MessageHeaderAccessor.java

@@ -600,7 +600,7 @@ public class MessageHeaderAccessor {
 
 		if (messageHeaders instanceof MutableMessageHeaders mutableHeaders) {
 			MessageHeaderAccessor headerAccessor = mutableHeaders.getAccessor();
-			if (requiredType == null || requiredType.isInstance(headerAccessor))  {
+			if (requiredType == null || requiredType.isInstance(headerAccessor)) {
 				return (T) headerAccessor;
 			}
 		}

spring-messaging/src/main/java/org/springframework/messaging/tcp/reactor/ReactorNetty2TcpClient.java

@@ -310,7 +310,7 @@ public class ReactorNetty2TcpClient<P> implements TcpOperations<P> {
 				}
 			});
 			Sinks.Empty<Void> completionSink = Sinks.empty();
-			TcpConnection<P> connection = new ReactorNetty2TcpConnection<>(inbound, outbound,  codec, completionSink);
+			TcpConnection<P> connection = new ReactorNetty2TcpConnection<>(inbound, outbound, codec, completionSink);
 			scheduler.schedule(() -> this.connectionHandler.afterConnected(connection));
 
 			inbound.withConnection(conn -> conn.addHandlerFirst(new StompMessageDecoder<>(codec)));

spring-messaging/src/main/java/org/springframework/messaging/tcp/reactor/ReactorNettyTcpClient.java

@@ -308,7 +308,7 @@ public class ReactorNettyTcpClient<P> implements TcpOperations<P> {
 				}
 			});
 			Sinks.Empty<Void> completionSink = Sinks.empty();
-			TcpConnection<P> connection = new ReactorNettyTcpConnection<>(inbound, outbound,  codec, completionSink);
+			TcpConnection<P> connection = new ReactorNettyTcpConnection<>(inbound, outbound, codec, completionSink);
 			scheduler.schedule(() -> this.connectionHandler.afterConnected(connection));
 
 			inbound.withConnection(conn -> conn.addHandlerFirst(new StompMessageDecoder<>(codec)));