public static void main(String[] args) throws IOException {

  FileInputStream fis = new FileInputStream("a.txt");

  ByteArrayOutputStream baos = new ByteArrayOutputStream();

  byte[] arr = new byte[5];
  int len;
  
  while((len = fis.read(arr)) != -1) {
   baos.write(arr, 0, len);
   //System.out.println(new String(arr,0,len));
  }

  System.out.println(baos);     

  fis.close();
}
}

public static void main(String[] args) throws IOException {

  FileInputStream fis = new FileInputStream("a.txt");

  ByteArrayOutputStream baos = new ByteArrayOutputStream();

  byte[] arr = new byte[5];
  int len;
  
  while((len = fis.read(arr)) != -1) {
   baos.write(arr, 0, len);
   //System.out.println(new String(arr,0,len));
  }

  System.out.println(baos);     

  fis.close();
}
}