Petstore

Question

Hi,
I am reading through the petstore source code.I cannot figure out how the first screen (main screen)initialized.When MainServlet is called,it suppose call init method in MainServlet,so i assume the main screen should be initialized in init method.But I didn't find where is it.Can someone help me on that?The MainServlet is copied bellow:/*
* $Id: MainServlet.java,v 1.14.4.8 2001/03/15 00:40:02 brydon Exp $
* Copyright 2001 Sun Microsystems, Inc. All rights reserved.
* Copyright 2001 Sun Microsystems, Inc. Tous droits r?erv?.
package com.sun.j2ee.blueprints.petstore.control.web;
import javax.servlet.ServletException;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.PrintWriter;
import java.io.OutputStreamWriter;
import java.beans.Beans;
import java.io.IOException;
import java.util.HashMap;
import java.util.Locale;
import javax.naming.NamingException;
import javax.naming.InitialContext;
import com.sun.j2ee.blueprints.petstore.util.JNDINames;
import com.sun.j2ee.blueprints.petstore.control.exceptions.SigninFailedException;
import com.sun.j2ee.blueprints.petstore.control.exceptions.GeneralFailureException;
import com.sun.j2ee.blueprints.util.tracer.Debug;
import com.sun.j2ee.blueprints.petstore.control.web.ModelManager;
import com.sun.j2ee.blueprints.petstore.control.web.CustomerWebImpl;
import com.sun.j2ee.blueprints.petstore.control.web.ScreenFlowXmlDAO;
import com.sun.j2ee.blueprints.petstore.control.web.RequestProcessor;
import com.sun.j2ee.blueprints.petstore.util.WebKeys;
import com.sun.j2ee.blueprints.petstore.util.JSPUtil;
public class MainServlet extends HttpServlet {
private HashMap urlMappings;
public void init() {
Debug.println("MainServlet: Initializing");
String requestMappingsURL = null;
try {
requestMappingsURL = getServletContext().getResource("/WEB-INF/xml/requestmappings.xml").toString();
} catch (java.net.MalformedURLException ex) {
Debug.println("ScreenFlowManager: initializing ScreenFlowManager malformed URL exception: " + ex);
urlMappings = ScreenFlowXmlDAO.loadRequestMappings(requestMappingsURL);
getServletContext().setAttribute(WebKeys.URLMappingsKey, urlMappings);
Debug.println("MainServlet: loaded urlMappings");
String serverType = null;
try {
InitialContext ic = new InitialContext();
serverType = (String)ic.lookup(JNDINames.SERVER_TYPE);
getServletContext().setAttribute(WebKeys.ServerTypeKey, serverType);
} catch (NamingException ex) {
Debug.println("Server Type not specified in deployment descriptor: using default J2ee Security Adapter");
getScreenFlowManager();
getRequestProcessor();
Debug.println("MainServlet: Initialization complete");
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
doGet(request, response);
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
String selectedURL = request.getPathInfo();
// the current tomcat is resetting the outputstream so this is a workaround
if ((selectedURL != null) && selectedURL.equals("/white")) return;
HttpSession session = request.getSession();
ScreenFlowManager screenManager = null;
ModelManager modelManager= (ModelManager)request.getSession().getAttribute(WebKeys.ModelManagerKey);
if ( modelManager == null ) {
try {
modelManager = (ModelManager) Beans.instantiate(this.getClass().getClassLoader(), "com.sun.j2ee.blueprints.petstore.control.web.ModelManager");
} catch (Exception exc) {
throw new ServletException ("Cannot create bean of class ModelManager");
session.setAttribute(WebKeys.ModelManagerKey, modelManager);
modelManager.init(getServletContext(), session);
Debug.println("MainServlet: url " + selectedURL);
// check if url is protected before processing request
URLMapping current = getURLMapping(selectedURL);
if ((current != null) && current.requiresSignin()) {
CustomerWebImpl customer = modelManager.getCustomerWebImpl();
if (customer.isLoggedIn()) {
doProcess(request);
} else {
String signinScreen = getScreenFlowManager().getSigninScreen();
session.setAttribute(WebKeys.CurrentScreen, signinScreen);
session.setAttribute(WebKeys.SigninTargetURL, selectedURL);
} else {
doProcess(request);
Default to the base language or the site.
If a language is found in the session use that template.
Locale locale = JSPUtil.getLocale(request.getSession());
getServletConfig().getServletContext().getRequestDispatcher(getScreenFlowManager().getTemplate(locale)).forward(request, response);
private void doProcess(HttpServletRequest request) throws ServletException {
try {
getRequestProcessor().processRequest(request);
getScreenFlowManager().getNextScreen(request);
} catch (Throwable ex) {
String className = ex.getClass().getName();
String exceptionScreen = getScreenFlowManager().getExceptionScreen(className);
Debug.println("MainServlet: target screen is: " + exceptionScreen);
// put the exception in the request
request.setAttribute("javax.servlet.jsp.jspException", ex);
if (exceptionScreen != null) {
request.getSession().setAttribute(WebKeys.CurrentScreen, exceptionScreen);
} else {
// send to general error screen
Debug.println("MainServlet: unknown exception: " + className);
throw new ServletException("MainServlet: unknown exception: " + className);
private RequestProcessor getRequestProcessor() {
RequestProcessor rp = (RequestProcessor)getServletContext().getAttribute(WebKeys.RequestProcessorKey);
if ( rp == null ) {
Debug.println("MainServlet: initializing request processor");
rp = new RequestProcessor();
rp.init(getServletContext());
getServletContext().setAttribute(WebKeys.RequestProcessorKey, rp);
return rp;
private ScreenFlowManager getScreenFlowManager() {
ScreenFlowManager screenManager = (ScreenFlowManager)getServletContext().getAttribute(WebKeys.ScreenManagerKey);
if (screenManager == null ) {
Debug.println("MainServlet: Loading screen flow definitions");
screenManager = new ScreenFlowManager();
screenManager.init(getServletContext());
getServletContext().setAttribute(WebKeys.ScreenManagerKey, screenManager);
return screenManager;
* The UrlMapping object contains information that will match
* a url to a mapping object that contains information about
* the current screen, the RequestHandler that is needed to
* process a request, and the RequestHandler that is needed
* to insure that the propper screen is displayed.
private URLMapping getURLMapping(String urlPattern) {
if ((urlMappings != null) && urlMappings.containsKey(urlPattern)) {
return (URLMapping)urlMappings.get(urlPattern);
} else {
return null;

Answer 1

If you look at the lifecycle of a servlet, after init either doGet or doPost gets called (depends on the HTTP method you used.) If you just enter the URL on the browser address bar and hit enter, a HTTP GET method is actually issued which is translated to doGet.
In doGet, the last line says getRequestDispatcher(...).forward(...)
This is where the servlet redirects to a new page. The argument to getRequestDispatcher is the URL which is gotten from getScreenFlowManager based on the locale.