Sắp xếp dòng trong file kích thước lớn

     private static void sort(String fi_name, String fo_name){
try{
                BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(fi_name),"UTF-8"));


                Map map=new TreeMap();


       String line="";
       while((line=reader.readLine())!=null){
               map.put(line,line);
       }


       reader.close();
       BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(fo_name), "UTF-8"));
       for(String val : map.values()){
               writer.write(val);
               writer.write('\n');
       }
       writer.close();
                } catch (Exception e) {
                      System.err.println("Exception: "+e.getMessage());
                }
}