test

The Java EE 5 Tutorial

JSP Pages

The template for the Duke’s Bookstore example, tut-install/javaeetutorial5/examples/web/bookstore3/web/template/template.jsp, is shown next. This page includes a JSP page that creates the screen definition and then uses the insert tag to insert parameters from the definition into the application screen.

<%@ taglib uri="/tutorial-template" prefix="tt" %>
<%@ page errorPage="/template/errorinclude.jsp" %>
<%@ include file="/template/screendefinitions.jsp" %>
<html>
<head>
<title>
<tt:insert definition="bookstore" parameter="title"/>
</title>
</head>
<body  bgcolor="#FFFFFF">
  <tt:insert definition="bookstore" parameter="banner"/>
<tt:insert definition="bookstore" parameter="body"/>
<center><em>Copyright &copy; 2004 Sun Microsystems, Inc. </em></center>
</body>
</html>

The tut-install/javaeetutorial5/examples/web/bookstore3/web/template/screendefinitions.jspf page creates a definition for the screen specified by the request attribute javax.servlet.forward.servlet_path:

<tt:definition name="bookstore"
screen="${requestScope
    [’javax.servlet.forward.servlet_path’]}">
    <tt:screen id="/bookstore">
    <tt:parameter name="title" value="Duke’s Bookstore"
        direct="true"/>
    <tt:parameter name="banner" value="/template/banner.jsp"
        direct="false"/>
    <tt:parameter name="body" value="/bookstore.jsp"
        direct="false"/>
    </tt:screen>
    <tt:screen id="/bookcatalog">
    <tt:parameter name="title" direct="true">
      <jsp:attribute name="value" >
        <fmt:message key="TitleBookCatalog"/>
      </jsp:attribute>
    </tt:parameter>
    <tt:parameter name="banner" value="/template/banner.jsp"
        direct="false"/>
        <tt:parameter name="body" value="/bookcatalog.jsp"
        direct="false"/>
    </tt:screen>
    ...
</tt:definition>

The template is instantiated by the Dispatcher servlet. Dispatcher first gets the requested screen. Dispatcher performs business logic and updates model objects based on the requested screen. For example, if the requested screen is /bookcatalog, Dispatcher determines whether a book is being added to the cart based on the value of the Add request parameter. It sets the price of the book if it’s on sale, and then adds the book to the cart. Finally, the servlet dispatches the request to template.jsp:

public class Dispatcher extends HttpServlet {
    @Resource
    UserTransaction utx;

    public void doGet(HttpServletRequest request,
        HttpServletResponse response) {
        String bookId = null;
        Book book = null;
        String clear = null;
        BookDBAO bookDBAO =
            (BookDBAO)getServletContext().
                getAttribute("bookDBAO");
        HttpSession session = request.getSession();
        String selectedScreen = request.getServletPath();
        ShoppingCart cart = (ShoppingCart)session.
            getAttribute("cart");
        if (cart == null) {
            cart = new ShoppingCart();
            session.setAttribute("cart", cart);
        }
        if (selectedScreen.equals("/bookcatalog")) {
            bookId = request.getParameter("Add");
            if (!bookId.equals("")) {
                try {
                    book = bookDBAO.getBook(bookId);
                    if ( book.getOnSale() ) {
                        double sale = book.getPrice() * .85;
                        Float salePrice = new Float(sale);
                        book.setPrice(salePrice.floatValue());
                    }
                    cart.add(bookId, book);
                } catch (BookNotFoundException ex) {
                    // not possible
                }
            }
        } else if (selectedScreen.equals("/bookshowcart")) {
            bookId =request.getParameter("Remove");
            if (bookId != null) {
                cart.remove(bookId);
            }
             clear = request.getParameter("Clear");
            if (clear != null && clear.equals("clear")) {
                cart.clear();
            }
        } else if (selectedScreen.equals("/bookreceipt")) {
        // Update the inventory
            try {
                utx.begin();
                bookDBAO.buyBooks(cart);
                utx.commit();
            } catch (Exception ex) {
                try {
                    utx.rollback();
                    request.getRequestDispatcher(
                        "/bookordererror.jsp").
                        forward(request, response);
                } catch(Exception e) {
                        System.out.println(
                            "Rollback failed: "+e.getMessage());
                        e.printStackTrace();
                }
            }
        }
        try {
            request.
                getRequestDispatcher(
                "/template/template.jsp").
                forward(request, response);
        } catch(Exception ex) {
            ex.printStackTrace();
        }
    }

    public void doPost(HttpServletRequest request,
        HttpServletResponse response) {
             request.setAttribute("selectedScreen",
            request.getServletPath());
        try {
            request.
                getRequestDispatcher(
                "/template/template.jsp").
                forward(request, response);
        } catch(Exception ex) {
            ex.printStackTrace();
        }
    }
}