static  Random rand =  new  Random();
   static   int  pRand( int  mod) {
     return  Math.abs(rand.nextInt()) % mod +  1 ;
  }

...

 public   void  doPost(HttpServletRequest request, HttpServletResponse response)  throws  ServletException, IOException {
     int  [] mas =  new   int [pRand( 20 )];
    
    URL url =  new  URL("http://server");
    URLConnection con = url.openConnection();
    con.setDoOutput(true);
    con.setUseCaches(false);    
    OutputStream outstream = con.getOutputStream();
    ObjectOutputStream oos =  new  ObjectOutputStream(outstream);
    oos.writeObject(mas);
    oos.flush();
    oos.close();

    response.sendRedirect("http://server");
  }

   public   void  doPost(HttpServletRequest request, HttpServletResponse response) 
            throws  ServletException, IOException {
    String str_1 = request.getParameter("in");
    String str_2 = request.getParameter("out");
    String url = "http://server";
    
     try  {
      HttpClient client =  new  HttpClient();
      PostMethod post =  new  PostMethod(url);
      post.addParameter(str_1, str_2);
       int  statusCode = client.executeMethod(post);
       if  (statusCode != - 1 ) {
        String contents = post.getResponseBodyAsString();
        post.releaseConnection();
        System.out.println(contents);
      }
    }
     catch  (Exception e) {
      e.printStackTrace();
    }
    
    response.sendRedirect(url);
  }