Learn Java for Web Development

CHAPTER 2: Building Web Applications Using Servlets and JSP 95

Listing 2-32. All Books Link in leftColumn.jsp

1.

   Line 2: This line is the All Books link displayed in the menu. When this link is

clicked, the value of action-allBooks is added to the URL as the parameter,

as shown in the URL:

http:localhost:8080/bookWeb/books?action=allBooks

Step 2, which is locating the servlet from the request, is executed, but this time the action is not null
and has a value allBooks. So, the code block in the doPost() method in the BookController, shown
in Listing 2-33, is executed.

Listing 2-33. All Books in the doPost( ) in BookController

1.protected void doPost(HttpServletRequest request,
2.HttpServletResponse response) throws ServletException, IOException {
3.String base = "/jsp/";
4.String url = base + "home.jsp";
5.String action = request.getParameter("action");
6.String category = request.getParameter("category");
7.String keyWord = request.getParameter("keyWord");
8.if (action != null) {
9.switch (action) {
10.case "allBooks":
11.findAllBooks(request, response);
12.url = base + "listOfBooks.jsp";
13.break;
14.case "category":
15.findAllBooks(request, response);
16.url = base + "category.jsp?category=" + category;
17.break;
18.case "search":
19.searchBooks(request, response, keyWord);
20.url = base + "searchResult.jsp";
21.break;
22.
23.}
24.}
25.RequestDispatcher requestDispatcher = getServletContext()
26..getRequestDispatcher(url);
27.requestDispatcher.forward(request, response);
28.}

   Line 8: The action is not null, and the value of the action is allBooks.

   Lines 10 to 12: The helper method findAllBooks(request, response) is invoked,

the URL is reconstructed to point to listOfBooks.jsp, and RequestDispatcher

forwards to the view provided to the RequestDispatcher in the form of a URL.