对一个和我有同样担忧的人...

<%@ page import="java.nio.charset.StandardCharsets"%>
<%@ page import="java.text.Normalizer"%>
<%@ page import="com.oreilly.servlet.MultipartRequest"%>

MultipartRequest multi = new MultipartRequest(request, upload_dir, maxsize, "UTF-8", "");

String originalFilename = multi.getFilesystemName("file"); 
String normalizedFilename = Normalizer.normalize(originalFilename, Normalizer.Form.NFC);

File oldFile = new File(upload_dir + File.separator + originalFilename);
File newFile = new File(upload_dir + File.separator + normalizedFilename);
if (!oldFile.renameTo(newFile)) {
    throw new IOException("Failed to rename uploaded file");
}

I solved through above code.