在JSP中执行代码之前，如何首先重定向到页面？

Question

在servlet doPost中执行response.sendRedirect（“ uploadcomplete.jsp”）之后，它会在显示整个页面之前执行Java代码

如何在执行Java代码之前先显示页面？

uploadSERVLET.java

public class uploadSERVLET extends HttpServlet {
  protected void doGet(...){
    response.sendRedirect("upload.html");
  }


  protected void doPost(...){
    // save uploaded file in server folder/db

    response.sendRedirect("uploadComplete.jsp");

    // do very long processing takes about 10-20~mins depending on the file uploaded
  }

}