1. Chapter 9 Web Applications
2026/2/10: Eve starts here
Yingcai Xiao

2. Enterprise Application Architectures

3. Main Issues for Developing Enterprise Applications
User Interface, Data Storage, Security, Business Logic, Networking.
To deal with those issues effectively, modern enterprise applications are usually designed as multi-tier applications.

4. A Two-tier Application (Client-Server)
Multi-tier Applications
Multi-tier Application: an application consists of multiple programs each may reside on a different system.
Client
Interconnection Network
Server
A Two-tier Application (Client-Server)

5. A Three-tier Application
Multi-tier Applications
A Three-tier Application
Client
Application Server
Interconnection Network
Database Server
In a three-tier application, a Database Server is an independent program deployed as a part of the application to store data.

6. A Four-tier Application
Multi-tier Applications
A Four-tier Application
Client
Database Server
Application Server
Internet
Web Server
A Web Server is added.
It uses the standard protocols (HTML/HTTP) to communicate with the client.
The client is thin: a standard web browser.

7. Multi-tier Applications
Client: interface to the user. It should be as thin as possible. Thin-client: no software to install on the client site except a standard web browser. Thin-client makes applications easy to deploy, easy to maintain and easy to upgrade.
Web Server: communicates with the user interface.
Application Server: business logic implemented here with tools from ASP.NET, J2EE, WebLogic (BEAS), WebSphere (IBM). Most application servers have separate modules to dynamically generate user interfaces to be sent to the client by the web server.
Database Server: persistent data stored for the application.
All three server could reside in the same server hardware.

8. J2EE Java 2 Enterprise Edition (http://java.sun.com/j2ee)
a platform for developing multi-tier enterprise applications with standardized modular Java components
provides a complete set of services to handle many details automatically
takes advantage of many features of the Java 2 Platform, Standard Edition (J2SE)

9. J2EE Application Architecture
Application Server (UI)
Application Server (BL)
DB Server
Thin
Client
Day 3/8/2016
Client
J2EE-Enabled Web Server

10. .NET Web Applications
.NET Web Applications are applications built for the Web using the .NET framework. The applications use Web forms to provide user interface, per-user data stores to hold shopping carts, caching services to boost performance, and security services to identify users and prevent unauthorized accesses.
.NET Web Applications are actually Application Servers in the four-tier architecture. Other programs (client, web server, database server) need to be there to make the applications work. The those programs can be shared with other applications.

11. Architecture of a Four-Tier Application
DBMS / Database Server
Application Server
WEB S E R V C L I N T
Database
User Interface
Database Engine
Supporting Software
Database API
Application Logic
App User Interface
Architecture of a Four-Tier Application

12. Architecture of a Three-Tier Application
DBMS / Database Server
Database
User Interface
Database Engine
Supporting Software
Application Server
Database API
Application Logic
App User Interface C L I E N T
Architecture of a Three-Tier Application

13. ASP.NET Web Application Structures

14. Structure of an ASP.NET Web Application
An ASP.NET application.
The Web.config File
To support XCOPY installs— to install applications by copying them to a directory and uninstall them by deleting the files and directories.

15. Structure of an ASP.NET Web Application
An ASP.NET (web) application (server) consists of all the files in a virtual directory and its subdirectories on the HW server.
ASPX files containing Web forms (unlimited)
ASCX files containing user controls (unlimited)
Web.config files containing configuration settings (one per directory)
A Global.asax file containing global application elements (only one for the entire application)
DLLs containing custom types employed by the application (unlimited, must be in the bin directory under the root of the virtual directory)

16. Create a Web Application in IIS
Server Manager->IIS Manager->winserv1 -> Sites -> Default Web Site
Right-click->Add Application (not Virtual Directory)
Alias: Lander
Application pool: defualtAppPool
Physical path: C:\inetpub\wwwroot\xiaotest\Lander
* You need to be an administrator to use IIS

17. Convert a directory to a Web Application in IIS
Existing directories can be converted to Web Applications
Server Manager->IIS Manager->winserv1 -> Sites -> Default Web Site->xiaotest
Right-click on Lander
Convert to Application
Alias: Lander
Application pool: defualtAppPool
* You need to be an administrator to use IIS

18. XML • Extensible Markup Language
• A markup language for documents containing structured information.
• The XML specification defines a standard way to add markups to documents to identify structures in a document.
• Both the tag semantics and the tag set are user definable.
• A meta-language for describing (defining) markup languages.
• Commonly used to describe data transmitted over the Internet. •

19. Web.config
Web.config is the XML file in which ASP.NET applications store configuration data.
• Not in the registry anymore.
• Case sensitive.
• Inherited, can be overridden by subdirectories.
• Machine.config is at the root. Under
Windows\Microsoft.NET\Framework\vn.n.nnnn\Config
7/3/2017; Done day 3/11/2015

20. Need to set custom error mode.
Runtime Error
Need to set custom error mode.

21. Error Message to the Users
<configuration>
<system.web>
<customErrors mode=“RemoteOnly” defaultRedirect=“errorMessage.html” />
</system.web>
</configuration>
Three custom errors modes
Off (default): displays system error message locally and remotely.
On: displays custom errorMessage.html locally and remotely.
RemoteOnly: displays debugging information locally and errorMessage.html remotely.

22. Debugging
• Use “RemoteOnly” to display debugging information locally and errorMessage.html remotely.
e.g.
Copy files from “Examples/c9/Debug” to a A.D.
Edit calc.aspx in it.
Change op1 in “OnAdd” to op11
Better view it with I.E.
Show Detailed Compiler Output

23. Debugging

24. Web.config
• Use system.web in .config to set system-wide configurations.
<!-- Web.Config Configuration File -->
<configuration>
<system.web>
<!-- To allow debug info displayed at the client -->
<customErrors mode="Off"/>
<trace enabled="true" />
</system.web>
</configuration>
‘customErrors mode="Off”’ means “systemErrors mode” on.
Day 3/8/2016

25. Web.config
Strings defined in the .config file can be retrieved in the program at run time:
string conn = ConfigurationSettings.AppSettings ["MyConnectionString"];
<!-- Web.Config Configuration File -->
<configuration>
<appSettings>
<add key="MyConnectionString"
value="server=db1; database=pubs; uid=sa; pwd=" />
<add key="connectString"
value="Integrated Security=true;Initial Catalog=pubs;
Data Source=XIAO-T23-01" />
</appSettings>
</configuration>
Evenning 3/11/2015

26. The Global.asax File • application-level
• text file
• application-level
• only one for each application
• directives
• event handlers
• declarations
Global Directives:
Application Description="My First ASP.NET Application" %>
Import Namespace="System.Data" %>
Assembly Name="System.DirectoryServices" %>

27. Global Event Handlers For events that aren’t specific to a
Global Event Handlers For events that aren’t specific to a particular page but that apply to the application as a whole: Application_Start, Application_End, Session_Start, Session_End, Application_Error.
An application consists of multiple pages (static structure).
An application can support multiple sessions at runtime, one for each client (dynamic structure).
Global Object Tags
       Session["MyShoppingCart"] = new ShoppingCart ();
To use in an application:
<object id="MyShoppingCart"
class="ShoppingCart"
scope="session" runat="server" />

28. Application State & Application Cache
• to improve application performance
• data stored in memory
• as dictionaries of key/value pairs
• string keys
• available to all parts of an application (global)
• Application Cache replaces Application State.

29. The Application Cache A per-application, in-memory data store.
• System.Web.Caching.Cache
Pages: Page.Cache
Global.asax: HttpApplication.Context.Cache
• Insert
Cache.Insert ("AMZN", 12.00);// or
Cache["AMZN"] = 10.00; // replace existing entry
• Remove
Cache.Remove ("AMZN");
• Usage
decimal amzn = (decimal) Cache["AMZN"];

30. The Application Cache • Locking
System.Threading.ReaderWriterLock rwlock.AcquireWriterLock (Timeout.Infinite);
• Expiration (new)
Absolute:
Context.Cache.Insert ("Stocks", stocks, null, DateTime.Now.AddMinutes(5),
Cache.NoSlidingExpiration();
Sliding (expires only if not accessed):
Cache.NoAbsoluteExpiration ();
• Cleaning Callbacks
Context.Cache.Insert (… ,
new CacheItemRemovedCallback (RefreshDataSet));

31. When Calc.aspx is accessed by a client
Session State: per-user store to support shopping cart (equivalent to global variables)
Challenge: the Web is stateless.
Client side store: cookies (users may disable cookies)
Server side store - in memory (down with IIS, no Web farms (clusters of Web servers act as one))
ASP.NET session store:
Cookies: client side store
Cookieless: server side store – in memory, in another process, on another machine, in a database

32. Session State Process Models
Description
In-proc
Stores session state in-process to ASP.NET (that is, in Aspnet_wp.exe) (default)
State Server
Stores session state in an external “state server” process on the Web server or on a remote machine (slower)
SQL Server
Stores session state in a Microsoft SQL Server database on the Web server or on a remote machine (slowest, scalable and reliable, for e-commerce)

33. Change session state type in Web.config
<sessionState mode="InProc" />
<sessionState mode="StateServer"
stateConnectionString="tcpip= :42424" />
<sessionState mode="SQLServer"
sqlConnectionString="server=localhost;uid=sa;pwd=" />
<sessionState mode="Off" />

34. Using Session State • Page access: System.Web.UI.Page.Session property
• Global.asax access: System.Web.HttpApplication.Session property
• Both map to an instance of System.Web.SessionState.HttpSessionState
• Add an item:
Session.Add (" ", "Quantity=1");
Session[" "] = "Quantity=1";
• Retrieving an item:
string value = Session[" "];

35. Using Session State • Retrieving all items:
NameObjectCollectionBase.KeysCollection keys
= Session.Keys;
foreach (string key in keys) {…}
• Remove, RemoveAt, and RemoveAll.
• Session timeout: <SessionState timeout="60" />
• Close session: Session.Abandon ();
• Session Identification:
using GUIDs (globally unique identifiers)
• Automatic lock and unlock

36. <%@ Page Language="C#" %> <html> <body> <%
Using Session State
Page Language="C#" %>
<html> <body> <%
if (Session.IsNewSession || Session["Count"] == null)
{ Session["Count"] = 1;
Response.Write ("Welcome! Because this is your first visit to this site, a new session has been created for you. Your session ID is " + Session.SessionID + "."); }
else { Session["Count"] = (int) Session["Count"] + 1;
Response.Write ("You have visited this site " +
Session["Count"] + " times. Your session ID is still " +
Session.SessionID + ".");
%> </body> </html>

37. Using Session State
A session is created for each client process and stored on the server. NS and IE are different processes.
To make your program work deterministically, your application needs to identify the user through the login authentication and respond accordingly (Chapter 10).

38. State Server or SQL Server session state models require types stored in session state to be serializable.
[Serializable]
public class ShoppingCart
{ }
ShoppingCart cart = new ShoppingCart ();
Session["MyShoppingCart"] = cart;

39. A mini enterprise application
Congo (C9)
Congo: A virtual storefront for an online bookseller.
Related to: database => data grid => shopping cart
Forms: Database supported, web based security.
Examples\C9\Congo-MySQL
Deployment: