Sorry I post this question again. I am sure some of you tried the Bookstore
example, you don't have any problem running it? Every
time I tried to follow the tutorials to learn more, I was blocked by
this question. Anybody can give an explanation? Thank you very
much!
Did you ever try the sample duke's bookstore provided by
javasoft. The BookDetailServlet and CatalogServlet always output
NullPointerException. I have worked on this for long time, right now my
major problem is: debugging message does not show on the javawebserver
console( when start the web server, leave it open, then message will show
up, I used to debug in this way), so I can not check where cause the NPE. I
use following code:
>> String bookId = request.getParameter("bookId");
>> try{
>> bookId = request.getParameter("bookId");
>> }catch(Exception e)
>> {
>> e.printStackTrace();
>> System.out.println(e.getMessage());
>> }
>> System.out.println("bookId is: "+bookId);
>>Nothing shows on the console.
The full version of BookDetailServlet.java is
>>here, gurus please help, the whole package is also attached for your
convenience(oops, the package is too large to go through, but
if you have javawebserver installed, it locates in the example/application
directory)
>>
>>import java.io.*;
>>import javax.servlet.*;
>>import javax.servlet.http.*;
>>import database.*;
>>import cart.ShoppingCart;
>>
>>
>>public class BookDetailServlet extends HttpServlet {
>>
>> public void doGet (HttpServletRequest request,
>> HttpServletResponse response)
>> throws ServletException, IOException
>> {
>> // Get the user's session and shopping cart
>> HttpSession session = request.getSession(true);
>> ShoppingCart cart =
>> (ShoppingCart)session.getValue(session.getId());
>>
>> // If the user has no cart, create a new one
>> if (cart == null) {
>> cart = new ShoppingCart();
>> session.putValue(session.getId(), cart);
>> }
>>
>> // set content-type header before accessing the Writer
>> response.setContentType("text/html");
>> PrintWriter out = response.getWriter();
>>
>> // then write the response
>> out.println("<html>" +
>> "<head><title>Book Description</title></head>" +
>>
>> "<body bgcolor=\"#FFFFFF\">" +
>> "<center>" +
>> "<hr> <br> " +
>> "<h1>" +
>> "<font size=\"+3\" color=\"red\">Duke's </font>" +
>> "<font size=\"+3\" color=\"purple\">Bookstore</font>"
+
>> "</h1>" +
>> "</center>" +
>> "<br> <hr> <br> ");
>>
>> //Get the identifier of the book to display
>> String bookId = request.getParameter("bookId");
>> if (bookId != null) {
>>
>> // and the information about the book
>> BookDBServlet database = (BookDBServlet)
>>
>getServletConfig().getServletContext().getServlet("bookdb");
>> BookDetails bd = database.getBookDetails(bookId);
>>
>> //Print out the information obtained
>> out.println("<h2>" + bd.getTitle() + "</h2>" +
>>
>> " By <em>" + bd.getFirstName() + ", " +
>> bd.getSurname() + "</em> " +
>> "(" + bd.getYear() + ")<br> <br>" +
>>
>> "<h4>Here's what the critics say: </h4>" +
>> "<blockquote>" + bd.getDescription() +
>> "</blockquote>" +
>>
>> "<h4>Our price: $" + bd.getPrice() + "</h4>" +
>>
>> "<center>" +
>> "<p><a href=\"" +
>> response.encodeUrl("/servlet/catalog?Buy=" +
>bookId)
>>+
>> "\"> Add this item to your shopping cart.</a></p>"
>+
>> "</center>");
>> }
>> out.println("</body></html>");
>> out.close();
>> }
>>
>> public String getServletInfo() {
>> return "The BookDetail servlet returns information about" +
>> "any book that is available from the bookstore.";
>> }
>>}
>>
>>
>
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