Synchronize RemoteFileUtils.makeDirectories()

https://stackoverflow.com/questions/55918648

Avoid the race with concurrent threads.

**cherry-pick to 5.x.x, 4.3.x**

(cherry picked from commit 130e1bb)

spring-integration-file/src/main/java/org/springframework/integration/file/remote/RemoteFileUtils.java

@@ -32,7 +32,9 @@
  */
 public final class RemoteFileUtils {
 
-	private RemoteFileUtils() { }
+	private RemoteFileUtils() {
+		super();
+	}
 
 	/**
 	 * Recursively create remote directories.
@@ -43,8 +45,8 @@ private RemoteFileUtils() { }
 	 * @param logger The logger.
 	 * @throws IOException Any IOException.
 	 */
-	public static <F> void makeDirectories(String path, Session<F> session, String remoteFileSeparator, Log logger)
-			throws IOException {
+	public static synchronized <F> void makeDirectories(String path, Session<F> session, String remoteFileSeparator,
+			Log logger) throws IOException {
 
 		if (!session.exists(path)) {