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

.

• To deal with those issues effectively, modern enterprise applications are usually designed as multi-tier applications.

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)

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.

Multi-tier Applications

A Four-tier Application Client Web Server Application Server Internet Database 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.

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.

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…

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

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

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

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?

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

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

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

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

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

view queries model

model-view-controller

view model controller updates model and/or view model signals changes controller controller updates model and/or view event event is passed to the controller

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

M-V-C for web applications

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

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

Controller for web applications

• controller handles events • user-generated events – client-side scripting – http request processing – redirection – preprocessing • system maintenance – web application management

presentation

M-V-C Example

request processing program logic Web Browser Web Server PHP /CGI view controller two-tier client-server architecture model

M-V-C Example

multi-tier client server architecture entity model Web Browser Web Server JSP /ASP /CF view controller view/ controller entity model

J2EE Web Application Structures

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)

Thin Client

J2EE Application Architecture

Application Server (UI) Application Server (BL) DB Server Client J2EE-Enabled Web Server

Architecture of a Three-Tier Application

Supporting Software User Interface Database Engine Database DBMS / Database Server App User Interface Application Logic Database API Application Server

Architecture of a Three-Tier Application

C L I E N T

ASP.NET Web Application Structures

.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

,

caching per-user data stores

services to boost

performance

to hold , and

shopping carts 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.

Architecture of a Four-Tier Application

Supporting Software User Interface Database Engine Database DBMS / Database Server App User Interface Application Logic Database API Application Server

Architecture of a Four-Tier Application

WEB S E R V E R WEB C L I E N T

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.

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)

Create a Web Application in IIS

    

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

* You need to be an administrator to use IIS

• • • • • • •

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.

http://www.xml.com/

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

•

Web.config

Use system.web in .config to set system-wide configurations.

‘customErrors mode="Off”’ means “systemErrors mode” on.

• •

Debugging

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

Web.config

” /> Three custom errors modes 1. On: displays custom errorMessage.html locally and remotely 2. Off ( default ): displays debugging information locally and remotely. ( Dangerous !) 3. RemoteOnly: displays debugging information locally and errorMessage.html remotely

Debugging

http://winserv1.cs.uakron.edu/Examples/c9/Debug/calc.aspx

Custom error mode

“

On

”

, but no defaultRedirect

Web.config

Default custom error mode is Off: very Dangerous !

Displays (code) debugging information locally and remotely.

Web.config

Strings defined in the .config file can be retrieved in the program at run time: string conn = ConfigurationSettings.AppSettings ["MyConnectionString"];

• • • • • •

The Global.asax File

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" %>



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: