Better way to create directories using File
Well, for the purpose of codereview:


There is a mkdirs() methods instead of the mkdir() method
You can use the new File(String, String) constructor to avoid taking care of slashes
If you have Java7, you can (and probably should) use Path. Especially, because there is a way to construct Paths with unlimited arguments, not only 2 as for File:

Path dir = Paths.get(rootPath, "media", userBean.getUsername(), arg1);
Files.createDirectories(dir);

You should check the return codes and errors. Could be helpful.