Descargar un fichero desde un servlet

resp.setContentType("application/download"); 
resp.setHeader("Content-Disposition", "attachment;filename=\"" + filename + "\""); 
 
ServletOutputStream out = resp.getOutputStream(); 
File file = null; 
BufferedInputStream from = null; 
try { 
  // en este ejemplo, filepath es el path completo después de la creación de un fichero temporal 
  file = new File(filepath); 
  resp.setContentLength((int) file.length()); 
  int bufferSize = 64 * 1024; 
  long time = System.currentTimeMillis(); 
  try { 
    from = new BufferedInputStream(new FileInputStream(file), bufferSize * 2); 
    byte[] bufferFile = new byte[bufferSize]; 
    for (int i = 0; ; i++) { 
      int len = from.read(bufferFile); 
      if (len < 0) break; 
      out.write(bufferFile, 0, len); 
    } 
    out.flush(); 
  } finally { 
    try { from.close(); } catch (Exception e) { } 
    try { out.close(); } catch (Exception e) {} } 
  time = (System.currentTimeMillis() - time) / 1000; // segundos download 
  double kb = (file.length() * 1.0 / 1024); 
  if (file != null) file.delete(); 
} catch (Exception e) { 
  return; 
} finally { 
  try { file.delete();} catch (Exception ex) {} 
}