(newbie) How to return error messages to JSP page.

Question

Hello,
I'm using a very simple Model 1 architecture (no framework such as Struts used.) The webapp just consists of a login.jsp which collects database connection parameters and then activates a servlet to return a PDF report to the browser.
I have a very common need: I would like the errors entered by the user on the login.jsp to be displayed at the top of a new return of the login.jsp (with the bottom of the JSP still providing the edit fields for reentry), errors such as:
1.) User did not enter the username, password, and database name
2.) Having a wrong username/password for the given database.
(2) is more complex than (1), because it would involve feedback from the servlet (which makes the DB connection).
I'm not sure how to code this, however, with just JSP, JSTL and JavaBeans. Does anyone know of an example with source code on the web where something similar to this is done?
Thanks,
Glen

Answer 1

No problem on posting here. Seeing as JSP forum is not accessible, this is the next best choice.
What sort of complexity are you after here?
You can go with the very simple:
Print out the error messages as you discover them.
if (request.getParameter("username") == null){
  // print out the message
  out.println("Please enter your username");
  // or alternatively
  List errors = new ArrayList();
  errors.add("Please enter your username");
}The best way to get feedback is to write your login method to return whether login succeeded or not. That can be a boolean true/false value, or you could return a User object to indicate success, and null to indicate failure.
How much of the code is in servlet, how much in JSP?