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Chapter 9 Web Applications

Chapter 9 Web Applications. Yingcai Xiao. Enterprise Application Architectures. Main Issues for Developing Enterprise Applications. User Interface, Data Storage, Security, Business Logic, Networking .

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Chapter 9 Web Applications

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  1. Chapter 9Web Applications 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. 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. 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. Client Web Server Internet Application Server Database Server Multi-tier Applications A Four-tier Application • 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. 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) J2EE

  9. Application Server (UI) Application Server (BL) DB Server Thin Client J2EE Application Architecture Client J2EE-Enabled Web Server

  10. .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. .NET Web Applications

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

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

  13. ASP.NET Web ApplicationStructures

  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. 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) Structure of an ASP.NET Web Application

  16. winserv1 -> Sites -> Default Web Site • Right-click->Add Application (not Virtual Directory) • Alias: xiaotestLander • Application pool: defualtAppPool • Physical path: C:\inetpub\wwwroot\xiaotest\Lander http://winserv1.cs.uakron.edu/xiaotestLander/Lander.aspx Existing directories can be converted to Web Applications • winserv1 -> Sites -> Default Web Site->xiaotest • Right-click on Lander • Convert to Application • Application pool: defualtAppPool • http://winserv1.cs.uakron.edu/xiaotest/Lander/Lander.aspx Create a Web Application in IIS * You need to be an administrator to use IIS

  17. • 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. • http://www.xml.com/ XML

  18. 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 Web.config

  19. • 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. Web.config

  20. • Each web application needs its own application directory. • For a web form application, the application directory containing the web form is treated as the root of the web “application”. 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. http://winserv1.cs.uakron.edu/Examples/c9/Debug/calc.aspx Show Detailed Compiler Output Debugging

  21. Debugging

  22. Web.config • <configuration> • <system.web> • <customErrors mode=“On” defaultRedirect=“errorMessage.html” /> • </system.web> • </configuration> • Three custom errors modes • On: displays custom errorMessage.html locally and remotely • Off (default): displays debugging information locally and remotely. (Dangerous!) • RemoteOnly: displays debugging information locally and errorMessage.html remotely

  23. Debugging http://winserv1.cs.uakron.edu/Examples/c9/Debug/calc.aspx Custom error mode “On”, but no defaultRedirect

  24. Web.config <configuration> </configuration> Default custom error mode is Off: very Dangerous! Displays (code) debugging information locally and remotely.

  25. 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> Web.config

  26. • 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" %> The Global.asax File

  27. 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 is replacing Application State.

  29. 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"]; The Application Cache

  30. • 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)); The Application Cache

  31. 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 When Calc.aspx is accessed by a client

  32. Session State Process Models

  33. Change session state type in Web.config <sessionState mode="InProc" /> <sessionState mode="StateServer" stateConnectionString="tcpip=192.168.1.2:42424" /> <sessionState mode="SQLServer" sqlConnectionString="server=localhost;uid=sa;pwd=" /> <sessionState mode="Off" />

  34. • 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 ("10012552", "Quantity=1"); Session["10012552"] = "Quantity=1"; • Retrieving an item: string value = Session["10012552"]; Using Session State

  35. • 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 Using Session State

  36. <%@ 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> Using Session State http://winserv1.cs.uakron.edu/examples/c9/sessionSpy/sessionSpy.aspx

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

  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. Congo (C9) Congo: A virtual storefront for an online bookseller. Related to: database => data grid => shopping cart Forms: Database supported, web based security. Deployment: http://www.cs.uakron.edu/~xiao/windows/Web-App-Deployment.html T:\Xiao\Windows Programming\Examples\C9\Congo-MySQL http://winserv1.cs.uakron.edu//xiaotest/Congo-MySQL/Congo.aspx Output format in C# http://blog.stevex.net/string-formatting-in-csharp/ A mini enterprise application

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