Java Reference
In-Depth Information
37.<welcome-file>default.htm</welcome-file>
38.<welcome-file>default.jsp</welcome-file>
39.</welcome-file-list>
40.</web-app>
Line 30
:
url-pattern/books
is mapped to the
BookServlet
in the
<servlet-mapping>
element, which is mapped to the servlet class
BookController
on line 9.
Lines 20 to 27
: We specify context parameters to the servlet in the
web.xml
file, since context parameters are available to the entire web app. When a
servlet instance is created, its
init()
method is called by the servlet container.
The
init()
method allows a servlet to initialize itself before the first request
is processed. We override the
init(ServletConfig config)
method in the
BookController
for getting the categories from the bookstore database.
These categories will be available to the entire application. The overridden
init(ServletConfig config)
in the
BookController
is illustrated in Listing 2-28.
Step 2 and Step 3: Accessing DB via DAO to Get the Categories from the
Database and Setting the Categories in the Model
Listing 2-28 shows the
BookController
.
Listing 2-28. init( ) Method in BookController
1.public void init(ServletConfig config) throws ServletException {
2.super.init(config);
3.BookDAO bookDao = new BookDAOImpl();
4.// calling DAO method to retrieve bookList from Database
5.List<Category> categoryList = bookDao.findAllCategories();
6.ServletContext context = config.getServletContext();
7.context.setAttribute("categoryList", categoryList);
8.}
Line 5
: This list of categories is obtained from the database by calling
findAllCategories()
on the
bookDao
object.
Line7
: The list of categories is set in the
ServletContext
so that the list is
available to the entire webapp.
Step 4: Dispatching to the View
As the
init()
method is completed in the previous step, the container calls the
service()
method of
the servlet (discussed in life-cycle methods of servlet). This method looks at the request, determines
the HTTP method, and invokes the matching
doget()
or
dopost()
on the servlet. Listing 2-29
illustrates the
doGet()
and
doPost()
methods of the servlet.
