Using JSP

Users do not request JSP pages the way they would request HTML pages.

Not requested directly

Instead, the user requests a URL that is mapped to a servlet, and the servlet chooses the JSP file.

Servlet selects JSP

Selecting the JSP File¶

Select the JSP file to display to the user by using a RequestDispatcher object, which you get from the HttpServletRequest.

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

  RequestDispatcher rd = req.getRequestDispatcher("/WEB-INF/view.jsp");

  // ...
}

Then call forward, passing the original request and response objects. * The JSP's servlet will now return a response.

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

  RequestDispatcher rd = req.getRequestDispatcher("/WEB-INF/view.jsp");
  rd.forward(req, resp);
}

We often do this all in one line.

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  // RequestDispatcher rd = req.getRequestDispatcher("/WEB-INF/view.jsp");
  // rd.forward(req, resp);
  req.getRequestDispatcher("/WEB-INF/view.jsp").forward(req, resp);
}

Selecting the JSP vs. Writing to the Response¶

We no longer need to write directly to the response using PrintWriter.println().

@Override
 public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
   // ...

   PrintWriter pw = resp.getWriter();
   pw.println("<html>");
   pw.println("<head><title>Stocks</title></head>");
   pw.print("<body>");
   // ...
   pw.close();
 }

* Instead, we just choose a JSP file and forward to it, and it will return its HTML content. * This is much better than having HTML code in our Java source.

Drill¶

In this drill you will change a servlet to execute a JSP instead of writing to the response directly.

JSPViews * Run the project. You will see options on the index page for using two versions of the StockServlet. For now, they are the same.

JSPViews/com.example.jsp.drills.servlets.StockServletJSP

Remove the entire contents of doGet.

Select the view /WEB-INF/select.jsp and call forward.

Run the app. It should look very different.

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