How to create a backup of a file using spring/?

Using java and FTP I managed to create a backup of a file by appending the TimeStamp with the file name, like

File: a.html 
Backup: a_Date_Time.html

but now when as I create a backup of the previous Backup, I get

File: a_Date_Time.html 
Backup: a_Date_Time_Date_Time.html

What is the best way to do this? And also Im trying to create a hashmap with, Original file as the key and all the backup as List of FtpFileInfo type

public HashMap<FtpFileInfo, List<FtpFileInfo>> viewFileMap(String directory) throws UnsupportedEncodingException {
    List<FtpFileInfo> file = gate.list("./" + URLDecoder.decode(directory, "UTF-8") + "/");
    fileMap = new HashMap<>();
    for (int i=0;i<file.size();i++){
        if(!file.get(i).isDirectory()){
            String name = file.get(i).getFilename().substring(0,file.get(i).getFilename().lastIndexOf("."));
            int length = name.length();
            fileList = new ArrayList<>();
           if(!name.matches("[\\w,\\s-]+_\\d{8}_\\d{6}")){
                for(int j=i+1;j<file.size();j++){
                    if(!file.get(j).isDirectory() && file.get(j).getFilename().substring(0,file.get(j).getFilename().lastIndexOf(".")).matches("[\\w,\\s-]+_\\d{8}_\\d{6}")){
                        String vocd = file.get(j).getFilename();
                        String fileName = vocd.substring(0, vocd.lastIndexOf("_"));
                        String finalFileName = fileName.substring(0, fileName.lastIndexOf("_"));
                        String ss = vocd.substring(vocd.substring(0, vocd.lastIndexOf("_")).lastIndexOf("_") + 1);
                        String timeStamp = ss.substring(0,ss.lastIndexOf("."));
                        if(name.equals(finalFileName) && isTimeStampValid(timeStamp)){
                            fileList.add(file.get(j));
                        }
                    }
                }
                fileMap.put(file.get(i),fileList);
            }
            else {
                continue;
            }
        }else {
            fileMap.put(file.get(i),null);
        }
    }
    return fileMap;
}

It works ok for