Controllerpublic class Controller extends HttpServlet | This is the Controller servlet for the ListManager web application. It must
be configured to be invoked in response to URLs ending with ".action". When
it is invoked this way, it uses the file name it is invoked as
("login.action", "edit.action", etc.) to determine what to do. Each
supported action name has a corresponding method which performs the
requested action and returns an appropriate View object in the form of a
a RequestDispatcher wrapped around a JSP page. The servlet dispatches to the
JSP page which generates an HTML document to display to the user. |
| Fields Summary |
|---|
| Connection | db | | UserFactory | userFactory |
| Methods Summary |
|---|
| public void | destroy()If the servlet is destroyed, we need to release the database connection
try { if (db != null) db.close(); }
catch(SQLException e) {}
| | public void | doGet(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse resp)
// Look up the information we need to dispatch this request
// We need to know what name we were invoked under and whether there
// is already a User object in the session.
String name = req.getServletPath();
User user = (User) req.getSession(true).getAttribute("user");
// This will hold the page we dispatch to for the response
RequestDispatcher nextPage;
// If no user is defined yet, go to the login page.
// Otherwise, dispatch to one of the methods below based on the name
// by which we were invoked (see web.xml for the mapping). The page
// to display is the return value of the method we dispatch to.
try {
if (name.endsWith("/login.action"))
nextPage = login(req, resp);
else if (user == null)
nextPage = req.getRequestDispatcher("login.jsp");
else if (name.endsWith("/edit.action"))
nextPage = edit(req, resp);
else if (name.endsWith("/unsubscribe.action"))
nextPage = unsubscribe(req, resp);
else if (name.endsWith("/logout.action"))
nextPage=logout(req, resp);
else {
// If we don't recoginze the name we're invoked under,
// send a HTTP 404 error.
resp.sendError(HttpServletResponse.SC_NOT_FOUND, "Not Found");
return;
}
}
catch(SQLException e) {
// If anything goes wrong while processing the action, then
// output an error page. This demonstrates how a servlet can
// produce its own output instead of forwarding to a JSP page.
// We could also use resp.sendError() here to send an error code.
resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
resp.setContentType("text/html");
PrintWriter out = resp.getWriter();
out.print("<h1>Error</h1>");
out.print("An unexpected error has occurred.<pre>");
out.print(e);
out.print("</pre>Please contact the webmaster.");
return;
}
// Now send the nextPage as the response to the client.
// See the RequestDispatcher class.
nextPage.forward(req, resp);
| | public void | doPost(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse resp)
doGet(req, resp);
| | javax.servlet.RequestDispatcher | edit(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse resp)
// Update the user's email delivery preferences based on request params
User user = (User) req.getSession().getAttribute("user");
user.setPrefersHTML(req.getParameter("html") != null);
user.setPrefersDigests(req.getParameter("digest") != null);
// Ask the factory to save the new preferences to the database
userFactory.update(user);
// And re-display the edit page
return req.getRequestDispatcher("edit.jsp");
| | public void | init()This method is called when the servlet is first created. It reads its
initialization parameters and uses them to connect to a database.
It uses the database connection to create a UserFactory object.
// Read initialization parameters from the web.xml deployment file
ServletConfig config = getServletConfig();
String jdbcDriver = config.getInitParameter("jdbcDriver");
String jdbcURL = config.getInitParameter("jdbcURL");
String jdbcUser = config.getInitParameter("jdbcUser");
String jdbcPassword = config.getInitParameter("jdbcPassword");
String tablename = config.getInitParameter("tablename");
// Use those parameters to connect to the database
try {
// Load the driver class.
// It registers itself; we don't need to retain the returned Class
Class.forName(jdbcDriver);
// Connect to database. If the database server ever crashes,
// this Connection object will become invalid, and the servlet
// will crash too, even if the database server has come back up.
db = DriverManager.getConnection(jdbcURL, jdbcUser, jdbcPassword);
// Use the DB connection to instantiate a UserFactory object
userFactory = new UserFactory(db, tablename);
}
catch(Exception e) {
log("Can't connect to database", e);
throw new ServletException("Can't connect to database", e);
}
// Save an init param where our JSP pages can find it. They need
// this so they can display the name of the mailing list.
ServletContext context = config.getServletContext();
context.setAttribute("listname",config.getInitParameter("listname"));
| | javax.servlet.RequestDispatcher | login(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse resp)
// This action can dispatch to one of two pages
RequestDispatcher loginPage = req.getRequestDispatcher("login.jsp");
RequestDispatcher editPage = req.getRequestDispatcher("edit.jsp");
// Get parameters from the request
String email = req.getParameter("email");
String password = req.getParameter("password");
// Make sure e-mail address is not the empty string!
if (email.length() == 0) {
req.setAttribute("loginMessage",
"You must specify an e-mail address");
return loginPage;
}
// Now try to subscribe or login. If all goes well, we'll end up
// with a User objectl
User user = null;
try {
// This action is either for subscribing a new user or for
// logging in an existing user. It depends on which submit button
// was pressed.
if (req.getParameter("subscribe") != null) {
// A new subscription
user = userFactory.insert(email, password);
}
else {
// A login
user = userFactory.select(email, password);
}
}
// If anything goes wrong, we send the user back to the login page
// with an error message.
catch(UserFactory.NoSuchUser e) {
req.setAttribute("loginMessage", "Unknown e-mail address.");
return loginPage;
}
catch(UserFactory.BadPassword e) {
req.setAttribute("loginMessage", "Incorrect Password");
return loginPage;
}
catch(UserFactory.UserAlreadyExists e) {
req.setAttribute("loginMessage", email + " is already subscribed");
return loginPage;
}
// If we got here, the user is subscribed or logged in. Store the User
// object in the current session and move on to the edit page.
HttpSession session = req.getSession(true);
session.setAttribute("user", user);
return editPage;
| | javax.servlet.RequestDispatcher | logout(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse resp)
// Destroy the session object, and return to the login page with
// a "logged out" message for confirmation.
User user = (User) req.getSession().getAttribute("user");
req.setAttribute("loginMessage", user.getEmailAddress()+" logged out");
req.getSession().invalidate(); // delete session
return req.getRequestDispatcher("login.jsp");
| | javax.servlet.RequestDispatcher | unsubscribe(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse resp)
// Get the User object from the session
User user = (User) req.getSession().getAttribute("user");
// Note the e-mail address before destroying it.
String email = user.getEmailAddress();
// Delete the suer from the database
userFactory.delete(user);
// Terminate the session
req.getSession().invalidate(); // log out
// Now display the login page again with a unsubscribed message
req.setAttribute("loginMessage",
email + " unsubscribed and logged out.");
return req.getRequestDispatcher("login.jsp");
|
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