Is it possible to use a JSP as a template for a servlet?

Question

I've been intermixing JSPs and Servlets in the web app I'm building and I'm starting to find that my more complex JSPs end up containing a lot of code, which flies in the face of all the MVC lessons that have been pounded into me. I know I can do this by just forwarding to the JSP, but this seems like a stupid hack.

What I'd like to do is use a servlet to do processing and then send a set of values to the JSP to render the HTML and return the response. Something along the lines of:

public class MyServlet extends HttpServlet {
 public void doGet(HttpServletRequest req, HttpServletResponse resp)
   throws IOException {

         // ... Do some processing

         resp.getWriter.print(renderJSP("mypage.jsp", values));

    }

}

I've been poking around Sun's documentation and found this: http://java.sun.com/developer/technicalArticles/javaserverpages/servlets_jsp/ It seems like the JSP Model 2 architecture is exactly what I want to implement, but I cannot find an example of how one can set that up. For technical reasons, I cannot use one of the more advanced template frameworks like Struts.

Is this possible or a lost cause?

Answer 1

Put the object(s) in the request, forward the request to the jsp page and then use the object(s) in the jsp to render the response.

In your servlet,

MyObject obj = ... //build somehow
request.setAttribute("myObject", obj);
RequestDispatcher rd = request.getRequestDispatcher("WEB-INF/jsp/my.jsp");
rd.forward(request, response);

If your result JSP should not be accessed directly from a URL you should hide it inside the WEB-INF directory where it can be accessed only through the forward directive.

Then on your jsp you can have,

<% MyObject obj = (MyObject) request.getAttribute("myObject"); %> 

To retrieve the object and used it as needed.

As others suggested, eventually it would be a good idea to learn to use JSTL and maybe an MVC framework like Spring MVC. The tutorial can be found here.

Answer 2

Put Java objects in the Request/Response/Session and use a javax.servlet.RequestDispatcher in your servlet, something like that:

RequestDispatcher dispatcher = request.getRequestDispatcher("/test.jsp");
dispatcher.forward(request,response);

A forward is server-side and the target servlet/JSP receives the same request/response objects as the original servlet/JSP. Therefore, you can pass data between them using request.setAttribute().

The other option is to use response.sendRedirect(String location) which is client-side (this method sends a temporary redirect response to the client) so the location URL receives a new request from the client, and the only way to pass data is through the session or with web parameters (url?name=value).

This is basically what MVC frameworks do (and no, it's not a hack).