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Web Applications Enterprise Application Architectures

Web Applications Enterprise Application Architectures. Dr. Mohammad Iqbal Thanks to Yingcai Xiao. Main Issues for Developing Enterprise Applications. User Interface, Data Storage, Security, Business Logic, Networking .

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Web Applications Enterprise Application Architectures

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  1. Web ApplicationsEnterprise Application Architectures Dr. Mohammad Iqbal Thanks to Yingcai Xiao

  2. 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.

  3. 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)

  4. 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.

  5. 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.

  6. 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.

  7. web applications • Applications delivered over the web! • Many server side components • N-tier architecture • Very wide range of functionality • web mail • online retail sales and auction sites • wikis, discussion boards, weblogs • multi-player online role-playing games, etc…

  8. software components of a web app • web server • configuration files • general processor components • e.g. PHP, ASP processor, XSLT processor • application-specific software • servelets • scripts

  9. data components of a web app • databases • possibly distributed or mirrored • session information • stateful servers retain session information • may persist in a database • global information • shared by all or many web app processes • e.g. number of hits on the site, user profiles

  10. file components of a web app • web pages • html files, stylesheets • script files, applets • images • dynamically generated pages • templates, e.g. PHP, ASP pages • xml files • web app architecture • structure definition and global data files

  11. design problems • construction and testing • how do we build a web application? • what technology should we choose? • re-use • can we use standard components? • scalability • how will our web application cope with • large numbers of requests? • large volumes of data exchanged?

  12. design problems • security • how do we protect against attack? • viruses • malicious data access • denial of service • different data views • user types • individual accounts • data protection

  13. design patterns • a design pattern is a general solution to a common software design problem • provides a development template • OO design patterns: • relationships and interactions between objects • not a finished design • the pattern must be adapted to the application • cannot simply translate into code

  14. design patterns • originally developed for architecture • Christopher Alexander • ideas were adapted to OO Design • Beck and Cunningham, 1987 • Design Patterns: elements of Re-useable Object-oriented software, 1994 • Reprinted and analysed many times • now widely-used in software engineering

  15. The Model-View-Controller Pattern • very widely used pattern • allows separation of development effort • model • contains data and system state • view • presents data and system state • controller • handles events affecting model or view

  16. model-view-controller • model knows little about the view • simply signals changes (alerts listeners) • view understands the model interface • uses model methods to get update data • controller knows model and view interfaces • updates model in response to events • updates view in response to events or changes in the model

  17. model-view-controller model controller updates model and/or view view queries model model signals changes view controller controller updates model and/or view event event is passed to the controller

  18. developing a M-V-C app • build the model • public methods become the interface for views and controller • build simple views to test the model • build the view(s) • use simple controllers to test view and model • build the controller • implement handling of all events • maintain • model remains fairly stable, views and controller may become more elaborate

  19. M-V-C for web applications

  20. Model for Web Applications • model consists of data and system state • database tables • persistent data • session information • current system state data • business logic (eCommerce) • rules governing the transaction

  21. View for web applications • view gives a presentation of the model • client-side presentation in a browser window • (D)HTML • CSS stylesheets • server-side templates • administrative information • server output logs

  22. Controller for web applications • controller handles events • user-generated events • client-side scripting • http request processing • redirection • preprocessing • system maintenance • web application management

  23. M-V-C Example presentation request processing program logic Web Browser Web Server PHP /CGI view controller model two-tier client-server architecture

  24. M-V-C Example model entity multi-tier client server architecture Web Browser Web Server JSP /ASP /CF database controller entity view view/ controller model

  25. J2EE Web ApplicationStructures

  26. 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

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

  28. 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

  29. ASP.NET Web ApplicationStructures

  30. .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

  31. 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

  32. 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.

  33. 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

  34. 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

  35. • 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

  36. 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

  37. • 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

  38. • 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

  39. Debugging

  40. 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

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

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

  43. 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

  44. • 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

  45. 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" />

  46. 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.

  47. 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

  48. • 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

  49. 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

  50. Session State Process Models

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