一个file实例

 File file = new File("src/ftp.txt");
  FileReader fd = new FileReader(file);
  BufferedReader br = new BufferedReader(fd);
  StringBuilder sb = new StringBuilder();
  String str = "";
  while ((str = br.readLine()) != null)
  {
  sb.append(str);
  sb.append("\n");
  }
  int lenth = 100;
  String str2=sb.toString();
  sb.setLength(0);
  for (int i = 1; i <= lenth; i++)
  {
  str=str2.replaceAll(temp1,i+"");
  sb.append(str);
  sb.append("\n");
  }
  FileOutputStream out=new FileOutputStream(file);
  out.write(sb.toString().getBytes());
  out.close();
  }